## [1212.5996] Merging neutron star binaries: equation of state and electrodynamics

Authors: Dong Lai

Date: 25 Dec 2012

Abstract: Merging neutron star (NS) binaries may be detected by ground-based gravitational wave (GW) interferometers (e.g. LIGO/VIRGO) within this decade and may also generate electromagnetic radiation detectable by wide-field, fast imaging telescopes that are coming online. The GWs can provide new constraint on the NS equation of state (including mass-radius relation and the related nuclear symmetry energy through resonant g-modes). This paper reviews various hydrodynamical (including equilibrium and dynamical/resonant tides) and electrodynamical processes in coalescing NS binaries, with focus on the pre-merger phase.

#### Dec 26, 2012

1212.5996 (/preprints)
2012-12-26, 20:24 

## [1212.4973] Gravitational waveforms for unequal mass black hole binaries detectable by KAGRA

Authors: M&#xe1;rton T&#xe1;pai, Zolt&#xe1;n Keresztes, L&#xe1;szl&#xf3; &#xc1;. Gergely

Date: 20 Dec 2012

Abstract: Gravitational waveforms generated by unequal mass black hole binaries are expected to be common sources for future gravitational wave detectors. We derived the waveforms emitted by such systems during the last part of the inspiral, when the larger spin dominates over the orbital angular momentum and the smaller spin is negligible. These Spin-Dominated Waveforms (SDW) arise as a double expansion in the post-Newtonian parameter and another parameter proportional to the ratio of the orbital angular momentum and the dominant spin. The time spent by the gravitational wave as an SDW in the sensitivity range of the KAGRA detector is presented for the first time.

#### Dec 21, 2012

1212.4973 (/preprints)
2012-12-21, 13:03 

## [1212.5202] Analysis of 3 years of data from the gravitational wave detectors EXPLORER and NAUTILUS

Authors: ROG Collaboration: P. Astone, M. Bassan, E. Coccia, S. D Antonio, V. Fafone, G. Giordano, A. Marini, Y. Minenkov, I. Modena, A. Moleti, G. V. Pallottino, G. Pizzella, A. Rocchi, F. Ronga, R. Terenzi, M. Visco

Date: 20 Dec 2012

Abstract: We performed a search for short gravitational wave bursts using about 3 years of data of the resonant bar detectors Nautilus and Explorer. Two types of analysis were performed: a search for coincidences with a low background of accidentals (0.1 over the entire period), and the calculation of upper limits on the rate of gravitational wave bursts. Here we give a detailed account of the methodology and we report the results: a null search for coincident events and an upper limit that improves over all previous limits from resonant antennas, and is competitive, in the range hrss 10ˆ{-19}, with limits from interferometric detectors. Some new methodological features are introduced that have proven successful in the upper limits evaluation.

#### Dec 21, 2012

1212.5202 (/preprints)
2012-12-21, 13:03 

## [1212.4730] Comparison of electromagnetic and gravitational radiation; what we can learn about each from the other

Authors: Richard H. Price, John W. Belcher, David A. Nichols

Date: 19 Dec 2012

Abstract: We compare the nature of electromagnetic fields and of gravitational fields in linearized general relativity. We carry out this comparison both mathematically and visually. In particular the "lines of force" visualizations of electromagnetism are contrasted with the recently introduced tendex/vortex eigenline technique for visualizing gravitational fields. Specific solutions, visualizations, and comparisons are given for an oscillating point quadrupole source. Among the similarities illustrated are the quasistatic nature of the near fields, the transverse 1/r nature of the far fields, and the interesting intermediate field structures connecting these two limiting forms. Among the differences illustrated are the meaning of field line motion, and of the flow of energy.

#### Dec 21, 2012

1212.4730 (/preprints)
2012-12-21, 13:03 

## [1212.5053] Neutron-star mergers in scalar-tensor theories of gravity

Authors: Enrico Barausse, Carlos Palenzuela, Marcelo Ponce, Luis Lehner

Date: 20 Dec 2012

Abstract: Scalar-tensor theories of gravity are among the most natural phenomenological alternatives to General Relativity, because the gravitational interaction is mediated by a scalar degree of freedom, besides the gravitons. In regions of the parameter space of these theories where constraints from both solar system experiments and binary-pulsar observations are satisfied, we show that binaries of neutron stars present marked differences from General Relativity in both the late-inspiral and merger phases. These strong-field effects are difficult to reproduce in General Relativity, even with an exotic equation of state. We comment on the relevance of our results for the upcoming Advanced LIGO/Virgo detectors.

#### Dec 21, 2012

1212.5053 (/preprints)
2012-12-21, 13:03 

## [1212.4357] Improved effective-one-body description of coalescing nonspinning black-hole binaries and its numerical-relativity completion

Authors: Thibault Damour, Alessandro Nagar, Sebastiano Bernuzzi

Date: 18 Dec 2012

Abstract: We improve the effective-one-body (EOB) description of nonspinning coalescing black hole binaries by incorporating several recent analytical advances, notably: (i) logarithmic contributions to the conservative dynamics; (ii) resummed horizon-absorption contribution to the orbital angular momentum loss; and (iii) a specific radial component of the radiation reaction force implied by consistency with the azimuthal one. We then complete this analytically improved EOB model by comparing it to accurate numerical relativity (NR) simulations performed by the Caltech-Cornell-CITA group for mass ratios $q=(1,2,3,4,6)$. In particular, the comparison to NR data allows us to determine with high-accuracy ($\sim 10ˆ{-4}$) the value of the main EOB radial potential: $A(u;\,\nu)$, where $u=GM/(R cˆ2)$ is the inter-body gravitational potential and $\nu=q/(q+1)ˆ2$ is the symmetric mass ratio. We introduce a new technique for extracting from NR data an intrinsic measure of the phase evolution, ($Q_\omega(\omega)$ diagnostics). Aligning the NR-completed EOB quadrupolar waveform and the NR one at low frequencies, we find that they keep agreeing (in phase and amplitude) within the NR uncertainties throughout the evolution for all mass ratios considered. We also find good agreement for several subdominant multipoles without having to introduce and tune any extra parameters.

#### Dec 21, 2012

1212.4357 (/preprints)
2012-12-21, 13:03 

## [1212.4810] Black hole-neutron star mergers at realistic mass ratios: Equation of state and spin orientation effects

Authors: Francois Foucart, M. Brett Deaton, Matthew D. Duez, Lawrence E. Kidder, Ilana MacDonald, Christian D. Ott, Harald P. Pfeiffer, Mark A. Scheel, Bela Szilagyi, Saul A. Teukolsky

Date: 19 Dec 2012

Abstract: Black hole-neutron star mergers resulting in the disruption of the neutron star and the formation of an accretion disk and/or the ejection of unbound material are prime candidates for the joint detection of gravitational-wave and electromagnetic signals when the next generation of gravitational-wave detectors comes online. However, the disruption of the neutron star and the properties of the post-merger remnant are very sensitive to the parameters of the binary. In this paper, we study the impact of the radius of the neutron star and the alignment of the black hole spin for systems within the range of mass ratio currently deemed most likely for field binaries (M_BH ~ 7 M_NS) and for black hole spins large enough for the neutron star to disrupt (J/Mˆ2=0.9). We find that: (i) In this regime, the merger is particularly sensitive to the radius of the neutron star, with remnant masses varying from 0.3M_NS to 0.1M_NS for changes of only 2 km in the NS radius; (ii) 0.01-0.05M_sun of unbound material can be ejected with kinetic energy >10ˆ51 ergs, a significant increase compared to low mass ratio, low spin binaries. This ejecta could power detectable optical and radio afterglows. (iii) Only a small fraction (1%-2%) of the Advanced LIGO events in this parameter range have gravitational-wave signals which could offer constraints on the equation of state of the neutron star. (iv) A misaligned black hole spin works against disk formation, with less neutron star material remaining outside of the black hole after merger, and a larger fraction of that material remaining in the tidal tail instead of the forming accretion disk. (v) Large kicks (v>300 km/s) can be given to the final black hole as a result of a precessing BHNS merger, when the disruption of the neutron star occurs just outside or within the innermost stable spherical orbit.

#### Dec 21, 2012

1212.4810 (/preprints)
2012-12-21, 13:03 

## [1212.3342] Deviation of Stellar Orbits from Test Particle Trajectories Around Sgr A* Due to Tides and Winds

Authors: Dimitrios Psaltis (Arizona), Gongjie Li (Harvard), Abraham Loeb (Harvard)

Date: 13 Dec 2012

Abstract: Monitoring the orbits of stars around Sgr A* offers the possibility of detecting the precession of their orbital planes due to frame dragging, of measuring the spin and quadrupole moment of the black hole, and of testing the no-hair theorem. Here we investigate whether the deviations of stellar orbits from test-particle trajectories due to wind mass loss and tidal dissipation of the orbital energy compromise such measurements. We find that the effects of stellar winds are, in general, negligible. On the other hand, for the most eccentric orbits (e>0.96) for which an optical interferometer, such as GRAVITY, will detect orbital plane precession due to frame dragging, the tidal dissipation of orbital energy occurs at timescales comparable to the timescale of precession due to the quadrupole moment of the black hole. As a result, this non-conservative effect is a potential source of systematic uncertainty in testing the no-hair theorem with stellar orbits.

#### Dec 17, 2012

1212.3342 (/preprints)
2012-12-17, 09:41 

## [1212.3169] The General Relativistic Two Body Problem and the Effective One Body Formalism

Authors: Thibault Damour

Date: 13 Dec 2012

Abstract: A new analytical approach to the motion and radiation of (comparable mass) binary systems has been introduced in 1999 under the name of Effective One Body (EOB) formalism. We review the basic elements of this formalism, and discuss some of its recent developments. Several recent comparisons between EOB predictions and Numerical Relativity (NR) simulations have shown the aptitude of the EOB formalism to provide accurate descriptions of the dynamics and radiation of various binary systems (comprising black holes or neutron stars) in regimes that are inaccessible to other analytical approaches (such as the last orbits and the merger of comparable mass black holes). In synergy with NR simulations, post-Newtonian (PN) theory and Gravitational Self-Force (GSF) computations, the EOB formalism is likely to provide an efficient way of computing the very many accurate template waveforms that are needed for Gravitational Wave (GW) data analysis purposes.

#### Dec 13, 2012

1212.3169 (/preprints)
2012-12-13, 18:40 

## [1212.2289] How Gravitational-wave Observations Can Shape the Gamma-ray Burst Paradigm

Authors: Imre Bartos, Patrick Brady, Szabolcs Marka

Date: 11 Dec 2012

Abstract: By reaching through shrouding blastwaves, efficiently discovering off-axis events, and probing the central engine at work, gravitational wave (GW) observations will soon revolutionize the study of gamma-ray bursts. Already, analyses of GW data targeting gamma-ray bursts have helped constrain the central engines of selected events. Advanced GW detectors with significantly improved sensitivities are under construction. After outlining the GW emission mechanisms from gamma-ray burst progenitors (binary coalescences, stellar core collapses, magnetars, and others) that may be detectable with advanced detectors, we review how GWs will improve our understanding of gamma-ray burst central engines, their astrophysical formation channels, and the prospects and methods for different search strategies. We place special emphasis on multimessenger searches. To achieve the most scientific benefit, GW, electromagnetic, and neutrino observations should be combined to provide greater discriminating power and science reach.

#### Dec 13, 2012

1212.2289 (/preprints)
2012-12-13, 08:46 

## [1212.2926] Light rays, gravitational waves, and pulse-time offsets

Date: 12 Dec 2012

Abstract: One might expect light to be scattered when it passes through a gravitational wave, and might hope that in favourable circumstances these scatterings could be observed on Earth even if the interaction occurs far away. Damour and Esposito-Far\‘ese, and Kopeikin, Sch\"afer, Gwinn and Eubanks, found that there were cancellations making such effects disappointingly small. Here I show that those cancellations depend on the emission of the light occurring far behind the gravity-wave source; for light-emissions near that source, larger effects are possible. I first develop a covariant treatment of the problem in exact general relativity (the propagation of light being modelled by geometric optics), and then specialise to linearised gravity. The most promising candidates identified here for detection in the not-too-distant future would involve sufficiently tight binaries as sources of gravitational radiation, and nearby pulsars as light-sources. In some favourable but not extreme cases, I find offsets in the pulses’ times of arrival at Earth by ~ 10ˆ{-10} -- 10ˆ{-9} s, with periods half the binaries' periods.

#### Dec 13, 2012

1212.2926 (/preprints)
2012-12-13, 08:46 

## [1212.1235] Black Holes are neither Particle Accelerators nor Dark Matter Probes

Authors: Sean T. McWilliams

Date: 6 Dec 2012

Abstract: It has been suggested that maximally spinning black holes can serve as particle accelerators, reaching arbitrarily high center-of-mass energies. Despite several objections regarding the practical achievability of such high energies, and demonstrations past and present that such large energies could never reach a distant observer, interest in this problem has remained substantial. We show that, unfortunately, a maximally spinning black hole can never serve as a probe of high energy collisions, even in principle and despite the correctness of the original diverging energy calculation. Black holes can indeed facilitate dark matter annihilation, but the most energetic photons can carry little more than the rest energy of the dark matter particles to a distant observer, and those photons are actually generated relatively far from the black hole where relativistic effects are negligible. Therefore, any strong gravitational potential could probe dark matter equally well, and an appeal to black holes for facilitating such collisions is unnecessary.

#### Dec 13, 2012

1212.1235 (/preprints)
2012-12-13, 08:45 

## [1212.2623] Binary Systems as Resonance Detectors for Gravitational Waves

Authors: Lam Hui, Sean T. McWilliams, I-Sheng Yang

Date: 11 Dec 2012

Abstract: Gravitational waves at suitable frequencies can resonantly interact with a binary system, inducing changes to its orbit. A stochastic gravitational-wave background causes the orbital elements of the binary to execute a classic random walk -- with the variance of orbital elements growing with time. The lack of such a random walk in binaries that have been monitored with high precision over long time-scales can thus be used to place an upper bound on the gravitational-wave background. Using periastron time data from the Hulse-Taylor binary pulsar spanning ~30 years, we obtain a bound of h_c < 7.9 x 10ˆ-14 at ~10ˆ-4 Hz, where h_c is the strain amplitude per logarithmic frequency interval. Our constraint complements those from pulsar timing arrays, which probe much lower frequencies, and ground-based gravitational-wave observations, which probe much higher frequencies. Interesting sources in our frequency band, which overlaps the lower sensitive frequencies of proposed space-based observatories, include white-dwarf/supermassive black-hole binaries in the early/late stages of inspiral, and TeV scale preheating or phase transitions. The bound improves as (time span)ˆ-2 and (sampling rate)ˆ-½. The Hulse-Taylor constraint can be improved to ~3.8 x 10ˆ-15 with a suitable observational campaign over the next decade. Our approach can also be applied to other binaries, including (with suitable care) the Earth-Moon system, to obtain constraints at different frequencies. The observation of additional binary pulsars with the SKA could reach a sensitivity of h_c ~ 3 x 10ˆ-17.

#### Dec 13, 2012

1212.2623 (/preprints)
2012-12-13, 08:45 

## [1212.2177] The experimental status of Special and General Relativity

Authors: Orfeu Bertolami, Jorge P&#xe1;ramos

Date: 10 Dec 2012

Abstract: In this contribution we assess the current experimental status of Special and General Relativity. Particular emphasis is put on putative extensions of these theories and on how these could be detected experimentally.

#### Dec 13, 2012

1212.2177 (/preprints)
2012-12-13, 08:45 

## [1212.1191] Three-Dimensional General-Relativistic Hydrodynamic Simulations of Binary Neutron Star Coalescence and Stellar Collapse with Multipatch Grids

Authors: C. Reisswig, R. Haas, C. D. Ott, E. Abdikamalov, P. Moesta, D. Pollney, E. Schnetter

Date: 5 Dec 2012

Abstract: We present a new three-dimensional general-relativistic hydrodynamic evolution scheme coupled to dynamical spacetime evolutions which is capable of efficiently simulating stellar collapse, isolated neutron stars, black hole formation, and binary neutron star coalescence. We make use of a set of adapted curvi-linear grids (multipatches) coupled with flux-conservative cell-centered adaptive mesh refinement. This allows us to significantly enlarge our computational domains while still maintaining high resolution in the gravitational-wave extraction zone, the exterior layers of a star, or the region of mass ejection in merging neutron stars. The fluid is evolved with a high-resolution shock capturing finite volume scheme, while the spacetime geometry is evolved using fourth-order finite differences. We employ a multi-rate Runge-Kutta time integration scheme for efficiency, evolving the fluid with second-order and the spacetime geometry with fourth-order integration, respectively. We validate our code by a number of benchmark problems: a rotating stellar collapse model, an excited neutron star, neutron star collapse to a black hole, and binary neutron star coalescence. The test problems, especially the latter, greatly benefit from higher resolution in the gravitational-wave extraction zone, causally disconnected outer boundaries, and application of Cauchy-characteristic gravitational-wave extraction. We show that we are able to extract convergent gravitational-wave modes up to (l,m)=(6,6). This study paves the way for more realistic and detailed studies of compact objects and stellar collapse in full three dimensions and in large computational domains. The multipatch infrastructure and the improvements to mesh refinement and hydrodynamics codes discussed in this paper will be made available as part of the open-source Einstein Toolkit.

#### Dec 13, 2012

1212.1191 (/preprints)
2012-12-13, 08:44 

## [1212.0837] Observing complete gravitational wave signals from dynamical capture binaries

Authors: William E. East, Sean T. McWilliams, Janna Levin, Frans Pretorius

Date: 4 Dec 2012

Abstract: We present a model for the inspiral, merger, and ringdown of highly eccentric compact binaries. We map the binary to an effective single black hole system described by a Kerr metric, thereby including certain relativistic effects not incorporated in existing post-Newtonian approximations. The resultant geodesics source quadrupolar radiation and in turn are evolved under its dissipative effects. At the light ring, we attach a merger model that was previously developed for quasicircular mergers but also performs well for eccentric mergers with little modification. We apply our model to assess the detectability of these sources for initial, Enhanced, and Advanced LIGO across the parameter space of nonspinning close capture compact binaries. We conclude that, should these systems exist in nature, the vast majority will be missed by conventional burst searches or by quasicircular waveform templates in the advanced detector era. Other methods, such as eccentric templates or, more practically, a stacked excess power search, must be developed to avoid losing these sources. These systems would also have been missed frequently in the initial LIGO data analysis. Thus, previous null coincidence results with detected GRBs can not exclude the possibility of coincident gravitational wave signals from eccentric binaries.

#### Dec 13, 2012

1212.0837 (/preprints)
2012-12-13, 08:44 

## [1211.6427] High Frequency Gravitational Waves from Supermassive Black Holes: Prospects for LIGO-Virgo Detections

Authors: Bence Kocsis

Date: 27 Nov 2012

Abstract: It is commonly assumed that ground-based gravitational wave (GW) instruments will not be sensitive to supermassive black holes (SMBHs) because the characteristic GW frequencies are far below the ~ 10 - 1000 Hz sensitivity bands of terrestrial detectors. Here, however, we explore the possibility of SMBH gravitational waves to leak to higher frequencies. In particular, if the high frequency spectral tail asymptotes to h(f) ~ fˆ(-alpha), where alpha<=2, then the spectral amplitude is a constant or increasing function of the mass M at a fixed frequency f>>cˆ3/GM. This will happen if the time domain waveform or its derivative exhibits a discontinuity. Ground based instruments could search for these universal spectral tails to detect or rule out such features irrespective of their origin. We identify the following processes which may generate high frequency signals: (i) gravitational bremsstrahlung of ultrarelativistic objects in the vicinity of a SMBH, (ii) ringdown modes excited by an external process that has a high frequency component or terminates abruptly, (iii) gravitational lensing echos and diffraction. More specifically for (iii), SMBHs produce GW echos of inspiraling stellar mass binaries in galactic nuclei with a delay of a few minutes to hours. We estimate the order of magnitude of the detection signal to noise ratio for each mechanism (i, ii, and iii) as a function of the waveform parameters.

#### Dec 04, 2012

1211.6427 (/preprints)
2012-12-04, 18:33 

## [1212.0232] General relativistic observables of the GRAIL mission

Authors: Slava G. Turyshev, Viktor T. Toth, Mikhail V. Sazhin

Date: 2 Dec 2012

Abstract: We present a realization of astronomical relativistic reference frames in the solar system and its application to the GRAIL mission. We model the necessary spacetime coordinate transformations for light-trip time computations and address some practical aspects of the implementation of the resulting model. We develop all the relevant relativistic coordinate transformations that are needed to describe the motion of the GRAIL spacecraft and to compute all observable quantities. We take into account major relativistic effects contributing to the dual one-way range observable, which is derived from one-way signal travel times between the two GRAIL spacecraft. We develop a general relativistic model for this fundamental observable of GRAIL, accurate to 1 $\mu$m. We develop and present a relativistic model for another key observable of this experiment, the dual one-way range-rate, accurate to 1 $\mu$m/s. The presented formulation justifies the basic assumptions behind the design of the GRAIL mission. It may also be used to further improve the already impressive results of this lunar gravity recovery experiment after the mission is complete. Finally, we present transformation rules for frequencies and gravitational potentials and their application to GRAIL.

#### Dec 04, 2012

1212.0232 (/preprints)
2012-12-04, 18:33 

## [1211.7099] Nonlinear Gravitational Recoil from the Mergers of Precessing Black-Hole Binaries

Authors: Carlos O. Lousto, Yosef Zlochower

Date: 29 Nov 2012

Abstract: We present results from an extensive study of 83 precessing, equal-mass black-hole binaries with large spins, a/m=0.8, and use these data to model new nonlinear contributions to the gravitational recoil imparted to the merged black hole. We find a new effect, the "cross kick", that enhances the recoil for partially aligned binaries beyond the "hangup kick" effect. This has the consequence of increasing the probabilities (by nearly a factor two) of recoils larger than 2000 km/s, and, consequently, of black holes getting ejected from galaxies and globular clusters, as well as the observation of large differential redshifts/blueshifts in the cores of recently merged galaxies.

#### Dec 03, 2012

1211.7099 (/preprints)
2012-12-03, 11:01 

## [1211.7090] Galactic Searches for Dark Matter

Authors: Louis E. Strigari

Date: 29 Nov 2012

Abstract: For nearly a century, more mass has been measured in galaxies than is contained in the luminous stars and gas. Through continual advances in observations and theory, it has become clear that the dark matter in galaxies is not comprised of known astronomical objects or baryonic matter, and that identification of it is certain to reveal a profound connection between astrophysics, cosmology, and fundamental physics. The best explanation for dark matter is that it is in the form of a yet undiscovered particle of nature, with experiments now gaining sensitivity to the most well-motivated particle dark matter candidates. In this article, I review measurements of dark matter in the Milky Way and its satellite galaxies and the status of Galactic searches for particle dark matter using a combination of terrestrial and space-based astroparticle detectors, and large scale astronomical surveys. I review the limits on the dark matter annihilation and scattering cross sections that can be extracted from both astroparticle experiments and astronomical observations, and explore the theoretical implications of these limits. I discuss methods to measure the properties of particle dark matter using future experiments, and conclude by highlighting the exciting potential for dark matter searches during the next decade, and beyond.

#### Dec 03, 2012

1211.7090 (/preprints)
2012-12-03, 11:01 

## [1211.7183] Bayesian Inference for LISA Pathfinder using Markov Chain Monte Carlo Methods

Authors: Luigi Ferraioli, Edward K. Porter, Eric Plagnol

Date: 30 Nov 2012

Abstract: We present a parameter estimation procedure based on a Bayesian framework by applying a Markov Chain Monte Carlo algorithm to the calibration of the dynamical parameters of a space based gravitational wave detector. The method is based on the Metropolis-Hastings algorithm and a two-stage annealing treatment in order to ensure an effective exploration of the parameter space at the beginning of the chain. We compare two versions of the algorithm with an application to a LISA Pathfinder data analysis problem. The two algorithms share the same heating strategy but with one moving in coordinate directions using proposals from a multivariate Gaussian distribution, while the other uses the natural logarithm of some parameters and proposes jumps in the eigen-space of the Fisher Information matrix. The algorithm proposing jumps in the eigen-space of the Fisher Information matrix demonstrates a higher acceptance rate and a slightly better convergence towards the equilibrium parameter distributions in the application to LISA Pathfinder data . For this experiment, we return parameter values that are all within $\sim1\sigma$ of the injected values. When we analyse the accuracy of our parameter estimation in terms of the effect they have on the force-per-unit test mass noise estimate, we find that the induced errors are three orders of magnitude less than the expected experimental uncertainty in the power spectral density.

#### Dec 03, 2012

1211.7183 (/preprints)
2012-12-03, 11:01 

## [1211.7095] Interpolation in waveform space: enhancing the accuracy of gravitational waveform families using numerical relativity

Authors: Kipp Cannon, J. D. Emberson, Chad Hanna, Drew Keppel, Harald Pfeiffer

Date: 29 Nov 2012

Abstract: Matched-filtering for the identification of compact object mergers in gravitational-wave antenna data involves the comparison of the data stream to a bank of template gravitational waveforms. Typically the template bank is constructed from phenomenological waveform models since these can be evaluated for an arbitrary choice of physical parameters. Recently it has been proposed that singular value decomposition (SVD) can be used to reduce the number of templates required for detection. As we show here, another benefit of SVD is its removal of biases from the phenomenological templates along with a corresponding improvement in their ability to represent waveform signals obtained from numerical relativity (NR) simulations. Using these ideas, we present a method that calibrates a reduced SVD basis of phenomenological waveforms against NR waveforms in order to construct a new waveform approximant with improved accuracy and faithfulness compared to the original phenomenological model. The new waveform family is given numerically through the interpolation of the projection coefficients of NR waveforms expanded onto the reduced basis and provides a generalized scheme for enhancing phenomenological models.

#### Dec 03, 2012

1211.7095 (/preprints)
2012-12-03, 11:01 

## [1211.6608] Multiple stellar-mass black holes in globular clusters: theoretical confirmation

Authors: Anna C. Sippel, Jarrod R. Hurley

Date: 28 Nov 2012

Abstract: While tens or hundreds of stellar-remnant black holes are expected to form in globular star clusters, it is still unclear how many of those will be retained upon formation, and how many will be ejected through subsequent dynamical interactions. No such black holes have been found in any Milky Way globular cluster until the recent discovery of stellar-mass black holes in the globular cluster M22 (NGC 6656) with now an estimated population of 5-100 black holes. We present a direct N-body model of a star cluster of the same absolute and dynamical age as M22. Imposing an initial retention fraction of approx. 10% for black holes, 16 stellar-remnant black holes are retained at a cluster age of 12 Gyr, in agreement with the estimate for M22. Of those 16 BHs, two are in a binary system with a main sequence star each while also one pure black hole binary is present. We argue that multiple black holes can be present in any Milky Way cluster with an extended core radius, such as M22 or the model presented here.

#### Nov 30, 2012

1211.6608 (/preprints)
2012-11-30, 21:53 

## [1211.6558] New tests of local Lorentz invariance and local position invariance of gravity with pulsars

Authors: Lijing Shao, Norbert Wex, Michael Kramer

Date: 28 Nov 2012

Abstract: New tests are proposed to constrain possible deviations from local Lorentz invariance and local position invariance in the gravity sector. By using precise timing results of two binary pulsars, i.e., PSRs J1012+5307 and J1738+0333, we are able to constrain (strong-field) parametrized post-Newtonian parameters $\hat{\alpha}_1$, $\hat{\alpha}_2$, $\hat{\xi}$ to high precision, among which, $|\hat{\xi}| < 3.1\times10ˆ{-4}$ (95% C.L.) is reported here for the first time.

#### Nov 30, 2012

1211.6558 (/preprints)
2012-11-30, 21:52 

## [1211.6884] A set of invariant quality factors measuring the deviation from the Kerr metric

Authors: Alfonso Garc&#xed;a-Parrado G&#xf3;mez-Lobo, Jos&#xe9; M. M. Senovilla

Date: 29 Nov 2012

Abstract: A number of scalar invariant characterizations of the Kerr solution are presented. These characterizations come in the form of quality factors defined in stationary space-times. A quality factor is a scalar quantity varying in the interval $[0,1]$ with the value 1 being attained if and only if the space-time is locally isometric to the Kerr solution. No knowledge of the Kerr solution is required to compute these quality factors. A number of different possibilities arise depending on whether the space-time is Ricci-flat and asymptotically flat, just Ricci-flat, or Ricci non-flat. In each situation a number of quality factors are constructed and analysed. The relevance of these quality factors is clear in any situation where one seeks a rigorous formulation of the statement that a space-time is "close" to the Kerr solution, such as: its non-linear stability problem, the asymptotic settlement of a radiating isolated system undergoing gravitational collapse, or in the formulation of some uniqueness results.

#### Nov 30, 2012

1211.6884 (/preprints)
2012-11-30, 21:51 

## [1211.6738] Sowing the seeds of massive black holes in small galaxies: Young clusters as the building blocks of Ultra-Compact-Dwarf Galaxies

Authors: Pau Amaro-Seoane, Symeon Konstantinidis, Marc Dewi Freitag, M. Coleman Miller, Frederic A. Rasio

Date: 28 Nov 2012

Abstract: Interacting galaxies often have complexes of hundreds of young stellar clusters of individual masses ~ 10ˆ{4-6} Msun in regions that are a few hundred parsecs across. These cluster complexes interact dynamically, and their coalescence is a candidate for the origin of some ultracompact dwarf galaxies (UCDs). Individual clusters with short relaxation times are candidates for the production of intermediate-mass black holes of a few hundred solar masses, via runaway stellar collisions prior to the first supernovae in a cluster. It is therefore possible that a cluster complex hosts multiple intermediate-mass black holes that may be ejected from their individual clusters due to mergers or binary processes, but bound to the complex as a whole. Here we explore the dynamical interaction between initially free-flying massive black holes and clusters in an evolving cluster complex. We find that, after hitting some clusters, it is plausible that the massive black hole will be captured in an ultracompact dwarf forming near the center of the complex. In the process, the hole typically triggers electromagnetic flares via stellar disruptions, and is also likely to be a prominent source of gravitational radiation for the advanced ground-based detectors LIGO and VIRGO. We also discuss other implications of this scenario, notably that the central black hole could be considerably larger than expected in other formation scenarios for ultracompact dwarfs.

#### Nov 30, 2012

1211.6738 (/preprints)
2012-11-30, 12:27 

## [1211.6184] Template banks to search for low-mass binary black holes in advanced gravitational-wave detectors

Authors: Duncan A. Brown, Prayush Kumar, Alexander H. Nitz

Date: 27 Nov 2012

Abstract: Coalescing binary black holes (BBHs) are among the most likely sources for the Laser Interferometer Gravitational-wave Observatory (LIGO) and its international partners Virgo and KAGRA. Optimal searches for BBHs require accurate waveforms for the signal model and effectual template banks that cover the mass space of interest. We investigate the ability of the second-order post-Newtonian TaylorF2 hexagonal template placement metric to construct an effectual template bank, if the template waveforms used are effective one body waveforms tuned to numerical relativity (EOBNRv2). We find that by combining the existing TaylorF2 placement metric with EOBNRv2 waveforms, we can construct an effectual search for BBHs with component masses in the range 3 Msolar <= m1, m2 <= 25 Msolar. We also show that the (computationally less expensive) TaylorF2 post-Newtonian waveforms can be used in place of EOBNRv2 waveforms when M <~ 12 Msolar. Finally, we investigate the effect of modes other than the dominant {l = m = 2} mode in BBH searches. We find that for systems with m1/m2 <= 1.5, there is no significant loss in the total possible signal-to-noise ratio due to neglecting modes greater than {l = m = 2} in the template waveforms. For higher mass ratios, including higher order modes could increase the signal-to-noise ratio by as much as 8% in Advanced LIGO. Our results can be used to construct matched-filter in Advanced LIGO and Advanced Virgo.

#### Nov 27, 2012

1211.6184 (/preprints)
2012-11-27, 18:53 

## [1211.5377] Gravitational waves and stalled satellites from massive galaxy mergers at z < 1

Authors: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

Date: 22 Nov 2012

Abstract: We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black-hole binary mergers in the low redshift universe (z < 1) implied by this model, and find that this population has a signal-to-noise ratio as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c(f =1 yrˆ{-1})=5.8 x 10ˆ{-15} that is already in tension with observational constraints, and a 2-sigma lower limit within this model of h_c(f =1 yrˆ{-1})=2.0 x 10ˆ{-15}. The strength of this signal may therefore be detectable with the data already collected using the current generation of pulsar timing arrays, and could be detected with high statistical significance under conservative assumptions within the next few years, if the principle assumption of merger-driven galaxy evolution since z=1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10ˆ{39} erg/s, which is consistent with the statistics of observed ULXs.

#### Nov 27, 2012

1211.5377 (/preprints)
2012-11-27, 18:53 

## [1211.5375] Systematic investigation of the expected gravitational wave signal from supermassive black hole binaries in the pulsar timing band

Authors: A. Sesana

Date: 22 Nov 2012

Abstract: In this letter we carry out the first systematic investigation of the expected gravitational wave (GW) background generated by supermassive black hole (SMBH) binaries in the nHz frequency band accessible to pulsar timing arrays (PTAs). We take from the literature several estimates of the redshift dependent galaxy mass function and of the fraction of close galaxy pairs to derive a wide range of galaxy merger rates. We then exploit empirical black hole-host relations to populate merging galaxies with SMBHs. The result of our procedure is a collection of a large number of phenomenological SMBH binary merger rates consistent with current observational constraints on the galaxy assembly at z<1.5. For each merger rate we compute the associated GW signal, eventually producing a large set of estimates of the nHz GW background that we use to infer confidence intervals of its expected amplitude. When considering the most recent SMBH-host relations, accounting for ultra-massive black holes in brightest cluster galaxies, we find that the nominal $1\sigma$ interval of the expected GW signal is only a factor of 3-to-10 below current PTA limits, implying a non negligible chance of detection in the next few years.

#### Nov 27, 2012

1211.5375 (/preprints)
2012-11-27, 09:23 

## [1211.6095] Black hole mass dynamics and renormalization group evolution

Authors: Walter D. Goldberger, Andreas Ross, Ira Z. Rothstein

Date: 26 Nov 2012

Abstract: We examine the real-time dynamics of a system of one or more black holes interacting with long wavelength gravitational fields. We find that the (classical) renormalizability of the effective field theory that describes this system necessitates the introduction of a time dependent mass counterterm, and consequently the mass parameter must be promoted to a dynamical degree of freedom. To track the time evolution of this dynamical mass, we compute the expectation value of the energy-momentum tensor within the in-in formalism, and fix the time dependence by imposing energy-momentum conservation. Mass renormalization induces logarithmic ultraviolet divergences at quadratic order in the gravitational coupling, leading to a new time-dependent renormalization group (RG) equation for the mass parameter. We solve this RG equation and use the result to predict heretofore unknown high order logarithms in the energy distribution of gravitational radiation emitted from the system.

#### Nov 27, 2012

1211.6095 (/preprints)
2012-11-27, 09:22 

## [1211.5601] Blocking low-eccentricity EMRIs: A statistical direct-summation N-body study of the Schwarzschild barrier

Authors: Patrick Brem, Pau Amaro-Seoane, Carlos F. Sopuerta

Date: 23 Nov 2012

Abstract: The capture of a compact object in a galactic nucleus by a massive black hole (MBH), an extreme-mass ratio inspiral (EMRI), is the best way to map space and time around it. Recent work on stellar dynamics has demonstrated that there seems to be a complot in phase space acting on low-eccentricity captures, since their rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques, and thus it affects the enhancement on lower-eccentricity EMRIs that one would expect from resonant relaxation. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian and also for the first time in a direct-summation code a geodesic approximation for the relativistic orbits. The existence of the barrier prevents low-eccentricity EMRIs from approaching the central MBH, but high-eccentricity EMRIs, which have been wrongly classified as "direct plunges" until recently, ignore the presence of the barrier, because they are driven by two-body relaxation. Hence, since the rates are significantly affected in the case of low-eccentricity EMRIs, we predict that a LISA-like observatory such as eLISA will predominantly detect high-eccentricity EMRIs.

#### Nov 27, 2012

1211.5601 (/preprints)
2012-11-27, 09:22 

## [1211.4609] Is there an intermediate massive black hole in the Galactic center: Imprints on the stellar tidal-disruption rate

Authors: Xian Chen (KIAA-PKU), F. K. Liu (PKU)

Date: 19 Nov 2012

Abstract: It has been suggested that an intermediate-massive black hole (IMBH) with mass 10ˆ{3-5} M_\odot could fall into the galactic center (GC) and form an massive black hole binary (MBHB) with the central supermassive black hole, but current observational are not sensitive to constrain all mass and distance ranges. Motivated by the recent discovery that MBHBs could enhance the rate of tidal-disruption events (TDEs) of stellar objects, we investigate the prospect of using stellar-disruption rate to probe IMBHs in the GC. We incorporated the perturbation by an IMBH into the loss-cone theory and calculated the stellar-disruption rates in the GC. We found that an IMBH heavier than 2000 M_\odot could distinguishably enhance the stellar-disruption rate. By comparing observations of Sgr A* with the fall-back model for stellar debris, we suggested that the TDE rate in our Galaxy should not significantly exceed 0.002 per year, therefore a fraction of the parameter space for the IMBH, concentrating at the high-mass end, can already be excluded. To derive constraint in the remaining parameter space, it is crucial to observationally confirm or reject the stellar-disruption rate between 10ˆ{-4} and 0.01 yrˆ{-1}, and we discussed possible strategies to make such measurements.

#### Nov 26, 2012

1211.4609 (/preprints)
2012-11-26, 11:43 

## [1211.4590] The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays

Authors: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

Date: 19 Nov 2012

Abstract: Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.

#### Nov 26, 2012

1211.4590 (/preprints)
2012-11-26, 11:43 

## [1211.3816] Is a tabletop search for Planck scale signals feasible

Authors: Jacob D. Bekenstein

Date: 16 Nov 2012

Abstract: Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.

#### Nov 26, 2012

1211.3816 (/preprints)
2012-11-26, 11:43 

## [1211.4107] Free motion around black holes with discs or rings: between integrability and chaos - II

Authors: O. Semer&#xe1;k, P. Sukov&#xe1;

Date: 17 Nov 2012

Abstract: We continue the study of time-like geodesic dynamics in exact static, axially and reflection symmetric space-times describing the fields of a Schwarzschild black hole surrounded by thin discs or rings. In the previous paper, the rise (and decline) of geodesic chaos with ring/disc mass and position and with test particle energy was revealed on Poincaré sections, on time series of position or velocity and their power spectra, and on time evolution of the orbital ‘latitudinal action’. In agreement with the KAM theory of nearly integrable dynamical systems and with the results observed in similar gravitational systems in the literature, we found orbits of very different degrees of chaoticity in the phase space of perturbed fields. Here we compare selected orbits in more detail and try to classify them according to the characteristics of the corresponding phase-variable time series, mainly according to the shape of the time-series power spectra, and also applying two recurrence methods: the method of ‘average directional vectors’, which traces the directions in which the trajectory (recurrently) passes through a chosen phase-space cell, and the ‘recurrence-matrix’ method, which consists of statistics over the recurrences themselves. All the methods proved simple and powerful, while it is interesting to observe how they differ in sensitivity to certain types of behaviour.

#### Nov 26, 2012

1211.4107 (/preprints)
2012-11-26, 11:43 

## [1211.4106] Free motion around black holes with discs or rings: between integrability and chaos - I

Authors: O. Semer&#xe1;k, P. Sukov&#xe1;

Date: 17 Nov 2012

Abstract: Geodesic dynamics is regular in the fields of isolated stationary black holes. However, due to the presence of unstable periodic orbits, it easily becomes chaotic under various perturbations. Here we examine what amount of chaoticity is induced in Schwarzschild space-time by a presence of an additional source. Following astrophysical motivation, we specifically consider thin rings or discs lying symmetrically around the hole, and describe the total field in terms of exact static and axially symmetric solutions of Einstein's equations. The growth of chaos in time-like geodesic motion is illustrated on Poincaré sections, on time series of position or velocity and their Fourier spectra, and on time evolution of the orbital ‘latitudinal action’. The results are discussed in dependence on the mass and position of the ring/disc and on geodesic parameters (energy and angular momentum). In the Introduction, we also add an overview of the literature.

#### Nov 26, 2012

1211.4106 (/preprints)
2012-11-26, 11:43 

## [1211.5091] The influence of star formation history on the gravitational wave signal from close double degenerates in the thin disc

Authors: Shenghua Yu, C. Simon Jeffery

Date: 21 Nov 2012

Abstract: The expected gravitational wave (GW) signal due to double degenerates (DDs) in the thin Galactic disc is calculated using a Monte Carlo simulation. The number of young close DDs that will contribute observable discrete signals in the frequency range $1.58 - 15.8$ mHz is estimated by comparison with the sensitivity of proposed GW observatories. The present-day DD population is examined as a function of Galactic star-formation history alone. It is shown that the frequency distribution, in particular, is a sensitive function of the Galactic star formation history and could be used to measure the time since the last major star-formation epoch.

#### Nov 25, 2012

1211.5091 (/preprints)
2012-11-25, 21:53 

## [1211.4871] On the orientation and magnitude of the black hole spin in galactic nuclei

Authors: M. Dotti, M. Colpi, S. Pallini, A. Perego, M. Volonteri

Date: 20 Nov 2012

Abstract: Massive black holes in galactic nuclei vary their mass M and spin vector J due to accretion. In this study we relax, for the first time, the assumption that accretion can be either chaotic, i.e. when the accretion episodes are randomly and isotropically oriented, or coherent, i.e. when they occur all in a preferred plane. Instead, we consider different degrees of anisotropy in the fueling, never confining to accretion events on a fixed direction. We follow the black hole growth evolving contemporarily mass, spin modulus a and spin direction. We discover the occurrence of two regimes. An early phase (M <~ 10 million solar masses) in which rapid alignment of the black hole spin direction to the disk angular momentum in each single episode leads to erratic changes in the black hole spin orientation and at the same time to large spins (a ~ 0.8). A second phase starts when the black hole mass increases above >~ 10 million solar masses and the accretion disks carry less mass and angular momentum relatively to the hole. In the absence of a preferential direction the black holes tend to spin-down in this phase. However, when a modest degree of anisotropy in the fueling process (still far from being coherent) is present, the black hole spin can increase up to a ~ 1 for very massive black holes (M >~ 100 million solar masses), and its direction is stable over the many accretion cycles. We discuss the implications that our results have in the realm of the observations of black hole spin and jet orientations.

#### Nov 25, 2012

1211.4871 (/preprints)
2012-11-25, 21:53 

## [1211.5535] Gravitational Waves from a Particle in Circular Orbits around a Schwarzschild Black Hole to the 22nd Post-Newtonian Order

Authors: Ryuichi Fujita

Date: 23 Nov 2012

Abstract: We extend our previous results of the 14th post-Newtonian (PN) order expansion of gravitational waves for a test particle in circular orbits around a Schwarzschild black hole to the 22PN order, i.e. $vˆ{44}$ beyond the leading Newtonian approximation where $v$ is the orbital velocity of a test particle. Comparing our 22PN formula for the energy flux with high precision numerical results, we find that the relative error of the 22PN flux at the innermost stable circular orbit is about $10ˆ{-5}$. We also estimate the phase difference between the 22PN waveforms and numerical waveforms after a two-year inspiral. We find that the dephase is about $10ˆ{-9}$ for $\mu/M=10ˆ{-4}$ and $10ˆ{-2}$ for $\mu/M=10ˆ{-5}$ where $\mu$ is the mass of the compact object and $M$ the mass of the central supermassive black hole. Finally, we construct a hybrid formula of the energy flux by supplementing the 4PN formula of the energy flux for circular and equatorial orbits around a Kerr black hole with all the present 22PN terms for the case of a Schwarzschild black hole. Comparing the hybrid formula with the the full numerical results, we examine the performance of the hybrid formula for the case of Kerr black hole.

#### Nov 25, 2012

1211.5535 (/preprints)
2012-11-25, 21:53 

## [1211.5410] First-Order Perturbative Hamiltonian Equations of Motion for a Point Particle Orbiting a Schwarzschild Black Hole

Authors: Huan Yang, Haixing Miao, Yanbei Chen

Date: 23 Nov 2012

Abstract: We formulate a spherical harmonically decomposed 1+1 scheme to self-consistently evolve the trajectory of a point particle and its gravitational metric perturbation to a Schwarzschild background spacetime. Following the work of Moncrief, we write down an action for perturbations in space-time geometry, combine that with the action for a point-particle, and then obtain Hamiltonian equations of motion for metric perturbations, the particle's coordinates, as well as their canonical momenta. Hamiltonian equations for the metric-perturbation and their conjugate momenta reduce to Zerilli-Moncrief and Regge-Wheeler master equations with source terms, which are gauge invariant, plus auxiliary equations that specify gauge. Hamiltonian equations for the particle, on the other hand, now include effect of metric perturbations - with these new terms derived from the same interaction Hamiltonian that had lead to those well-known source terms. In this way, space-time geometry and particle motion can be evolved in a self-consistent manner, in principle in any gauge. However, the point-particle nature of our source requires regularization, and we outline how the Detweiler-Whiting approach can be applied. In this approach, a singular field can be obtained using Hadamard decomposition of the Green's function and the regular field, which needs to be evolved numerically, is the result of subtracting the singular field from the total metric perturbation. In principle, any gauge that has the singular-regular field decomposition is suitable for our self-consistent scheme. In reality, however, this freedom is only possible if our singular field has a high enough level of smoothness. In the case of Lorenz gauge, for each l and m, we have 2 wave equations to evolve gauge invariant quantities and 8 first order differential equations to fix the gauge and determine the metric components.

#### Nov 25, 2012

1211.5410 (/preprints)
2012-11-25, 21:53 

## [1211.3258] Seeking for the leading actor on the cosmic stage: Galaxies versus Supermassive Black Holes

Authors: Angela Bongiorno, Francesco Shankar, Francesca Civano, Isabelle Gavignaud, Antonis Georgakakis

Date: 14 Nov 2012

Abstract: We present a Special Issue on the interplay of galaxies and Supermassive Black Holes (SMBHs) recently published in Advances in Astronomy. This is the introductory paper containing the motivation for this Special Issue together with a brief description of the articles which are part of the manuscript and the link to the entire book (this http URL). We hope this Special Issue will be useful for many astronomers who want to get an update on the current status of the AGN-Galaxy coevolution topic.

#### Nov 15, 2012

1211.3258 (/preprints)
2012-11-15, 23:05 

## [1211.3372] Retention of Stellar-Mass Black Holes in Globular Clusters

Authors: Meagan Morscher, Stefan Umbreit, Will M. Farr, Frederic A. Rasio

Date: 14 Nov 2012

Abstract: Globular clusters should be born with significant numbers of stellar-mass black holes (BHs). It has been thought for two decades that very few of these BHs could be retained through the cluster lifetime. With masses ~10 MSun, BHs are ~20 times more massive than an average cluster star. They segregate into the cluster core, where they may eventually decouple from the remainder of the cluster. The small-N core then evaporates on a short timescale. This is the so-called Spitzer instability. Here we present the results of a full dynamical simulation of a globular cluster containing many stellar-mass BHs with a realistic mass spectrum. Our Monte Carlo simulation code includes detailed treatments of all relevant stellar evolution and dynamical processes. Our main finding is that old globular clusters could still contain many BHs at present. In our simulation, we find no evidence for the Spitzer instability. Instead, most of the BHs remain well-mixed with the rest of the cluster, with only the innermost few tens of BHs segregating significantly. Over the 12 Gyr evolution, fewer than half of the BHs are dynamically ejected through strong binary interactions in the cluster core. The presence of BHs leads to long-term heating of the cluster, ultimately producing a core radius on the high end of the distribution for Milky Way globular clusters (and those of other galaxies). A crude extrapolation from our model suggests that the BH--BH merger rate from globular clusters could be comparable to the rate in the field.

#### Nov 15, 2012

1211.3372 (/preprints)
2012-11-15, 23:05 

## [1211.3651] Alignment of Magnetized Accretion Disks and Relativistic Jets with Spinning Black Holes

Authors: Jonathan C. McKinney (1 and 2), Alexander Tchekhovskoy (3), Roger D. Blandford (1) ((1) Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, (2) University of Maryland at College Park, Dept. of Physics, Joint Space-Science Institute, (3) Center for Theoretical Science, Jadwin Hall, Princeton University, Princeton Center for Theoretical Science Fellow)

Date: 15 Nov 2012

Abstract: Accreting black holes (BHs) produce intense radiation and powerful relativistic jets, which are affected by the BH's spin magnitude and direction. While thin disks might align with the BH spin axis via the Bardeen-Petterson effect, this does not apply to jet systems with thick disks. We used fully three-dimensional general relativistic magnetohydrodynamical simulations to study accreting BHs with various BH spin vectors and disk thicknesses with magnetic flux reaching saturation. Our simulations reveal a "magneto-spin alignment" mechanism that causes magnetized disks and jets to align with the BH spin near BHs and further away to reorient with the outer disk. This mechanism has implications for the evolution of BH mass and spin, BH feedback on host galaxies, and resolved BH images for SgrA* and M87.

#### Nov 15, 2012

1211.3651 (/preprints)
2012-11-15, 23:04 

## [1211.3138] Pulsars are cool. Seriously

Authors: Scott M. Ransom

Date: 13 Nov 2012

Abstract: Ever since the first pulsar was discovered by Bell and Hewish over 40 years ago, we've known that not only are pulsars fascinating and truly exotic objects, but that we can use them as powerful tools for basic physics and astrophysics as well. Taylor and Hulse hammered these views home with their discovery and timing of the spectacular "binary pulsar" in the 1970s and 1980s. In the last two decades a host of surprises and a promise of phenomenal scientific riches in the future has come from the millisecond pulsars. As our instrumentation has become more sensitive and better suited to measuring the pulses from these objects, they've given us new tests of general relativity, fantastic probes of the interstellar medium, constraints on the physics of ultra-dense matter, new windows into binary and stellar evolution, and the promise of a direct detection of gravitational waves. These things really are cool, and there is much more we will do with them in the future.

#### Nov 15, 2012

1211.3138 (/preprints)
2012-11-15, 22:48 

## [1211.2748] Spinning dust radiation: a review of the theory

Authors: Yacine Ali-Ha&#xef;moud

Date: 12 Nov 2012

Abstract: This article reviews the current status of theoretical modeling of electric dipole radiation from spinning dust grains. The fundamentally simple problem of dust grain rotation appeals to a rich set of concepts of classical and quantum physics, owing the the diversity of processes involved. Rotational excitation and damping rates through various mechanisms are discussed, as well as methods of computing the grain angular momentum distribution function. Assumptions on grain properties are reviewed. The robustness of theoretical predictions now seems mostly limited by the uncertainties regarding the grains themselves, namely their abundance, dipole moments, size and shape distribution.

#### Nov 13, 2012

1211.2748 (/preprints)
2012-11-13, 17:42 

## [1211.2457] Probing gravitation with pulsars

Authors: Michael Kramer (MPI fuer Radioastronomie, Bonn, Germany / Jodrell Bank Centre for Astrophysics, University of Manchester, UK)

Date: 11 Nov 2012

Abstract: Radio pulsars are fascinating and extremely useful objects. Despite our on-going difficulties in understanding the details of their emission physics, they can be used as precise cosmic clocks in a wide-range of experiments -- in particular for probing gravitational physics. While the reader should consult the contributions to these proceedings to learn more about this exciting field of discovering, exploiting and understanding pulsars, we will concentrate here on on the usage of pulsars as gravity labs.

#### Nov 13, 2012

1211.2457 (/preprints)
2012-11-13, 17:40 

## [1211.1060] First Law of Mechanics for Black Hole Binaries with Spins

Authors: Luc Blanchet, Alessandra Buonanno, Alexandre Le Tiec

Date: 5 Nov 2012

Abstract: We use the canonical Hamiltonian formalism to generalize to spinning point particles the first law of mechanics established for binary systems of non-spinning point masses moving on circular orbits [Le Tiec, Blanchet, and Whiting, Phys. Rev. D 85, 064039 (2012)]. We find that the redshift observable of each particle is related in a very simple manner to the canonical Hamiltonian and, more generally, to a class of Fokker-type Hamiltonians. Our results are valid through linear order in the spin of each particle, but hold also for quadratic couplings between the spins of different particles. The knowledge of spin effects in the Hamiltonian allows us to compute spin-orbit terms in the redshift variable through 2.5PN order, for circular orbits and spins aligned or anti-aligned with the orbital angular momentum. To describe extended bodies such as black holes, we supplement the first law for spinning point-particle binaries with some "constitutive relations" that can be used for diagnosis of spin measurements in quasi-equilibrium initial data.

#### Nov 08, 2012

1211.1060 (/preprints)
2012-11-08, 23:07 

## [1211.1254] Towards Rapid Parameter Estimation on Gravitational Waves from Compact Binaries using Interpolated Waveforms

Authors: R. J. E. Smith, K. Cannon, C. Hanna, D. Keppel, I. Mandel

Date: 6 Nov 2012

Abstract: Accurate parameter estimation of gravitational waves from coalescing compact binary sources is a key requirement for gravitational-wave astronomy. Evaluating the posterior probability density function of the binary's parameters (component masses, sky location, distance, etc.) requires computing millions of waveforms. The computational expense of parameter estimation is dominated by waveform generation and scales linearly with the waveform computational cost. Previous work showed that gravitational waveforms from non-spinning compact binary sources are amenable to a truncated singular value decomposition, which allows them to be reconstructed via interpolation at fixed computational cost. However, the accuracy requirement for parameter estimation is typically higher than for searches, so it is crucial to ascertain that interpolation does not lead to significant errors. Here we provide a proof of principle to show that interpolated waveforms can be used to recover posterior probability density functions with negligible loss in accuracy with respect to non-interpolated waveforms. This technique has the potential to significantly increase the efficiency of parameter estimation.

#### Nov 08, 2012

1211.1254 (/preprints)
2012-11-08, 23:07 

## [1211.1227] Gravitational waves signal analysis

Authors: Ll. Bel

Date: 5 Nov 2012

Abstract: I use a very simplified example to discuss the signature of a gravitational wave taking into account the relative state of motion of the detector with respect to the source that originated it. Something that to my knowledge has been ignored up to now and may ruin the best crafted template \cite{Templates}.

#### Nov 08, 2012

1211.1227 (/preprints)
2012-11-08, 23:07 

## [1211.1374] Testing General Relativity and gravitational physics using the LARES satellite

Authors: Ignazio Ciufolini, Antonio Paolozzi, Erricos Pavlis, John Ries, Vahe Gurzadyan, Rolf Koenig, Richard Matzner, Roger Penrose, Giampiero Sindoni

Date: 6 Nov 2012

Abstract: The discovery of the accelerating expansion of the Universe, thought to be driven by a mysterious form of ‘dark energy’ constituting most of the Universe, has further revived the interest in testing Einstein's theory of General Relativity. At the very foundation of Einstein's theory is the geodesic motion of a small, structureless test-particle. Depending on the physical context, a star, planet or satellite can behave very nearly like a test-particle, so geodesic motion is used to calculate the advance of the perihelion of a planet's orbit, the dynamics of a binary pulsar system and of an Earth orbiting satellite. Verifying geodesic motion is then a test of paramount importance to General Relativity and other theories of fundamental physics. On the basis of the first few months of observations of the recently launched satellite LARES, its orbit shows the best agreement of any satellite with the test-particle motion predicted by General Relativity. That is, after modelling its known non-gravitational perturbations, the LARES orbit shows the smallest deviations from geodesic motion of any artificial satellite. LARES-type satellites can thus be used for accurate measurements and for tests of gravitational and fundamental physics. Already with only a few months of observation, LARES provides smaller scatter in the determination of several low-degree geopotential coefficients (Earth gravitational deviations from sphericity) than available from observations of any other satellite or combination of satellites.

#### Nov 08, 2012

1211.1374 (/preprints)
2012-11-08, 23:06 

## [1211.1385] Binary Millisecond Pulsar Discovery via Gamma-Ray Pulsations

Authors: H. J. Pletsch, L. Guillemot, H. Fehrmann, B. Allen, M. Kramer, C. Aulbert, M. Ackermann, M. Ajello, A. de Angelis, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, A. W. Borgland, E. Bottacini, T. J. Brandt, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, &#xd6;. Celik, E. Charles, R.C.G. Chaves, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Cutini, F. D&#x27;Ammando, C. D. Dermer, S. W. Digel, P. S. Drell, A. Drlica-Wagner, R. Dubois, D. Dumora, C. Favuzzi, E. C. Ferrara, A. Franckowiak, Y. Fukazawa, P. Fusco, F. Gargano, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, G. Godfrey, I. A. Grenier, M.-H. Grondin, J. E. Grove, S. Guiriec, D. Hadasch, Y. Hanabata, A. K. Harding, P. R. den Hartog, M. Hayashida, E. Hays, A. B. Hill, X. Hou, R. E. Hughes, G. Johannesson, M. S. Jackson, T. Jogler, A. S. Johnson, W. N. Johnson, J. Kataoka, M. Kerr, J. Kn&#xf6;dlseder, M. Kuss, J. Lande, S. Larsson, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, M. N. Lovellette, P. Lubrano, F. Massaro, M. Mayer, M. N. Mazziotta, J. E. McEnery, J. Mehault, P. F. Michelson, W. Mitthumsiri, T. Mizuno, M. E. Monzani, A. Morselli, I. V. Moskalenko, S. Murgia, T. Nakamori, R. Nemmen, E. Nuss, M. Ohno, T. Ohsugi, N. Omodei, M. Orienti, E. Orlando, F. de Palma, D. Paneque, J. S. Perkins, F. Piron, G. Pivato, T. A. Porter, S. Raino, R. Rando, P. S. Ray, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, R. W. Romani, C. Romoli, D. A. Sanchez, P. M. Saz Parkinson, A. Schulz, C. Sgro, E. do Couto e Silva, E. J. Siskind, D. A. Smith, G. Spandre, P. Spinelli, D. J. Suson, H. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo, M. Tinivella, E. Troja, T. L. Usher, J. Vandenbroucke, V. Vasileiou, G. Vianello, V. Vitale, A. P. Waite, B. L. Winer, K. S. Wood, M. Wood, Z. Yang, S. Zimmer

Date: 6 Nov 2012

Abstract: Millisecond pulsars (MSPs), old neutron stars spun-up by accreting matter from a companion star, can reach high rotation rates of hundreds of revolutions per second. Until now, all such "recycled" rotation-powered pulsars have been detected by their spin-modulated radio emission. In a computing-intensive blind search of gamma-ray data from the Fermi Large Area Telescope (with partial constraints from optical data), we detected a 2.5-millisecond pulsar, PSR J1311-3430. This unambiguously explains a formerly unidentified gamma-ray source that had been a decade-long enigma, confirming previous conjectures. The pulsar is in a circular orbit with an orbital period of only 93 minutes, the shortest of any spin-powered pulsar binary ever found.

#### Nov 08, 2012

1211.1385 (/preprints)
2012-11-08, 23:05 

## [1210.7238] Comparing H-alpha and HI Surveys as Means to a Complete Local Galaxy Catalog in the Advanced LIGO/Virgo Era

Authors: Brian D. Metzger, David L. Kaplan, Edo Berger

Date: 26 Oct 2012

Abstract: Identifying the electromagnetic counterparts of gravitational wave (GW) sources detected by upcoming networks of advanced ground-based interferometers will be challenging due in part to the large number of unrelated astrophysical transients within the ~10-100 square degree sky localizations. A potential way to greatly reduce the number of such false positives is to limit detailed follow-up to only those candidates near galaxies within the GW sensitivity range of ~200 Mpc for binary neutron star mergers. Such a strategy is currently hindered by the fact that galaxy catalogs are grossly incomplete within this volume. Here we compare two methods for completing the local galaxy catalog: (1) a narrow-band H-alpha imaging survey; and (2) an HI emission line radio survey. Using H-alpha fluxes, stellar masses (M_star), and star formation rates (SFR) from galaxies in the Sloan Digital Sky Survey (SDSS), combined with HI data from the GALEX Arecibo SDSS Survey and the Herschel Reference Survey, we estimate that a H-alpha survey with a luminosity sensitivity of L_H-alpha = 1e40 erg/s at 200 Mpc could achieve a completeness of f_SFR ~ 75% with respect to total SFR, but only f_Mstar ~ 33% with respect to stellar mass (due to lack of sensitivity to early-type galaxies). These numbers are significantly lower than those achieved by an idealized spectroscopic survey due to the loss of H-alpha flux resulting from resolving out nearby galaxies and the inability to correct for the underlying stellar continuum. An HI survey with sensitivity similar to the proposed WALLABY survey on ASKAP could achieve f_SFR ~ 80% and f_Mstar ~ 50%, somewhat higher than that of the H-alpha survey. Finally, both H-alpha and HI surveys should achieve > 50% completeness with respect to the host galaxies of short duration gamma-ray bursts, which may trace the population of binary neutron star mergers.

#### Nov 06, 2012

1210.7238 (/preprints)
2012-11-06, 11:53 

## [1211.0546] Degeneracy between mass and spin in black-hole-binary waveforms

Authors: Emily Baird, Stephen Fairhurst, Mark Hannam, Patricia Murphy

Date: 2 Nov 2012

Abstract: We explore the degeneracy between mass and spin in gravitational waveforms emitted by black-hole binary coalescences. We focus on spin-aligned waveforms and obtain our results using phenomenological models that were tuned to numerical-relativity simulations. A degeneracy is known for low-mass binaries (particularly neutron-star binaries), where gravitational-wave detectors are sensitive to only the inspiral phase, and the waveform can be modelled by post-Newtonian theory. Here, we consider black-hole binaries, where detectors will also be sensitive to the merger and ringdown, and demonstrate that the degeneracy persists across a broad mass range. At low masses, the degeneracy is between mass ratio and total spin, with chirp mass accurately determined. At higher masses, the degeneracy persists but is not so clearly characterised by constant chirp mass as the merger and ringdown become more significant. We consider the importance of this degeneracy both for performing searches (including searches where only non-spinning templates are used) and in parameter extraction from observed systems. We compare observational capabilities between the early (~2015) and final (2018 onwards) versions of the Advanced LIGO detector.

#### Nov 06, 2012

1211.0546 (/preprints)
2012-11-06, 11:53 

## [1210.7969] Metric perturbations from eccentric orbits on a Schwarzschild black hole: I. Odd-parity Regge-Wheeler to Lorenz gauge transformation and two new methods to circumvent the Gibbs phenomenon

Authors: Seth Hopper, Charles R. Evans

Date: 30 Oct 2012

Abstract: We calculate the odd-parity, radiative ($\ell \ge 2$) parts of the metric perturbation in Lorenz gauge caused by a small compact object in eccentric orbit about a Schwarzschild black hole. The Lorenz gauge solution is found via gauge transformation from a corresponding one in Regge-Wheeler gauge. Like the Regge-Wheeler gauge solution itself, the gauge generator is computed in the frequency domain and transferred to the time domain. The wave equation for the gauge generator has a source with a compact, moving delta-function term and a discontinuous non-compact term. The former term allows the method of extended homogeneous solutions to be applied (which circumvents the Gibbs phenomenon). The latter has required the development of new means to use frequency domain methods and yet be able to transfer to the time domain while avoiding Gibbs problems. Two new methods are developed to achieve this: a partial annihilator method and a method of extended particular solutions. We detail these methods and show their application in calculating the odd-parity gauge generator and Lorenz gauge metric perturbations. A subsequent paper will apply these methods to the harder task of computing the even-parity parts of the gauge generator.

#### Nov 05, 2012

1210.7969 (/preprints)
2012-11-05, 08:51 

## [1210.8066] Observing extreme-mass-ratio inspirals with eLISA/NGO

Authors: Jonathan R Gair, Edward K Porter

Date: 30 Oct 2012

Abstract: The extreme-mass-ratio inspirals (EMRIs) of stellar mass compact objects into massive black holes in the centres of galaxies are an important source of low-frequency gravitational waves for space-based detectors. We discuss the prospects for detecting these sources with the evolved Laser Interferometer Space Antenna (eLISA), recently proposed as an ESA mission candidate under the name NGO. We show that NGO could observe a few tens of EMRIs over its two year mission lifetime at redshifts z < 0.5 and describe how the event rate changes under possible alternative specifications of the eLISA design.

#### Nov 05, 2012

1210.8066 (/preprints)
2012-11-05, 08:51 

## [1210.8152] Compact Binary Progenitors of Short Gamma-Ray Bursts

Authors: Bruno Giacomazzo, Rosalba Perna, Luciano Rezzolla, Eleonora Troja, Davide Lazzati

Date: 30 Oct 2012

Abstract: In recent years, detailed observations and accurate numerical simulations have provided support to the idea that mergers of compact binaries containing either two neutron stars (NSs) or an NS and a black hole (BH) may constitute the central engine of short gamma-ray bursts (SGRBs). The merger of such compact binaries is expected to lead to the production of a spinning BH surrounded by an accreting torus. Several mechanisms can extract energy from this system and power the SGRBs. Here we make the novel connection between observations and numerical simulations of compact binary mergers, and use the current sample of SGRBs with measured energies to constrain the mass of their powering tori. By comparing the masses of the tori with the results of fully general-relativistic simulations, we are able, for the first time, to infer the properties of the binary progenitors which yield SGRBs. We find that most of the tori have masses smaller than 0.01 M_{sun}, favoring "high-mass" binary NSs mergers, i.e. binaries with total masses >~1.5 the maximum mass of an isolated NS. This has important consequences for the GW signals that may be detected in association with SGRBs, since "high-mass" systems do not form a long-lived hypermassive NS (HMNS) after the merger. While NS-BH systems cannot be excluded to be the engine of at least some of the SGRBs, the BH would need to have an initial spin of ~0.9, or higher.

#### Nov 05, 2012

1210.8152 (/preprints)
2012-11-05, 08:50 

## [1210.7857] Corner-cube retro-reflector instrument for advanced lunar laser ranging

Authors: Slava G. Turyshev, James G. Williams, William M. Folkner, Gary M. Gutt, Richard T. Baran, Randall C. Hein, Ruwan P. Somawardhana, John A. Lipa, Suwen Wang

Date: 29 Oct 2012

Abstract: Lunar laser ranging (LLR) has made major contributions to our understanding of the Moon's internal structure and the dynamics of the Earth-Moon system. Because of the recent improvements of the ground-based laser ranging facilities, the present LLR measurement accuracy is limited by the retro-reflectors currently on the lunar surface, which are arrays of small corner-cubes. Because of lunar librations, the surfaces of these arrays do not, in general, point directly at the Earth. This effect results in a spread of arrival times, because each cube that comprises the retroreflector is at a slightly different distance from the Earth, leading to the reduced ranging accuracy. Thus, a single, wide aperture corner-cube could have a clear advantage. In addition, after nearly four decades of successful operations the retro-reflectors arrays currently on the Moon started to show performance degradation; as a result, they yield still useful, but much weaker return signals. Thus, fresh and bright instruments on the lunar surface are needed to continue precision LLR measurements. We have developed a new retro-reflector design to enable advanced LLR operations. It is based on a single, hollow corner cube with a large aperture for which preliminary thermal, mechanical, and optical design and analysis have been performed. The new instrument will be able to reach an Earth-Moon range precision of 1-mm in a single pulse while being subjected to significant thermal variations present on the lunar surface, and will have low mass to allow robotic deployment. Here we report on our design results and instrument development effort.

#### Nov 05, 2012

1210.7857 (/preprints)
2012-11-05, 08:50 

## [1211.0038] Black hole solutions of modified gravity theories

Authors: Yannis Bardoux

Date: 31 Oct 2012

Abstract: The main interest of the work exposed in this thesis is to explore hairy black holes in a more general framework than General Relativity by taking into account the presence of a cosmological constant, of higher dimensions, of exotic matter fields or of higher curvature terms. These extensions to General Relativity can be derived in the context of String Theory. It is also by studying natural extensions to General Relativity that we can more deeply understand the theory of Einstein. Firstly, we will display the theory of General Relativity with its building blocks in particular and we will give the mathematical tools that we need afterwards. Then, a first extension will be detailed with the introduction of higher dimensions and p-form fields which constitute the natural generalization of the electromagnetic interaction. We will build in this framework new static black hole solutions where p-form fields allow to shape the geometry of the horizon. Secondly, we will present the general extension of Einstein theory in any dimension which produces second order field equations: Lovelock theory. We will determine in this context a large class of solutions in dimension 6 for which the theory is reduced to Einstein-Gauss-Bonnet theory with the presence of p-form fields. Thirdly, we will study a generalization of General Relativity in dimension 4 whose modification is induced by a conformally coupled scalar field. We will namely exhibit a new black hole solution with a flat horizon in the presence of axionic fields. To conclude this thesis, thermodynamical aspects of these gravitational theories will be studied. In this way, we will be able to determine the mass and the charges of these new solutions and we will examine phase transition phenomena in the presence of a conformally scalar field.

#### Nov 05, 2012

1211.0038 (/preprints)
2012-11-05, 08:48 

## [1211.0013] Scaling Relations Between Low-mass Black Holes and Their Host Galaxies

Authors: Qirong Zhu, Yuexing Li, Sydney Sherman

Date: 31 Oct 2012

Abstract: It is well established that supermassive black holes in nearby elliptical galaxies correlate tightly with the kinematic property ($\mbhsigma$ correlation) and stellar mass ($\mbhhost$ correlation) of their host spheroids. However, it is not clear what the relations would be at the low-mass end, and how they evolve. Here, we investigate these relations in low-mass systems ($\MBH \sim \rm{10ˆ{6}- 10ˆ{8}}\, \Msun$) using the Aquila Simulation, a high-resolution cosmological hydrodynamic simulation which follows the formation and evolution of stars and black holes in a Milky Way-size galaxy and its substructures. We find a number of interesting results on the origin and evolution of the scaling relations in these systems: (1) there is a strong redshift evolution in the $\mbhsigma$ relation, but a much weaker one in the $\mbhhost$ relation; (2) there is a close link between the $\mbhsigma$ relation and the dynamical state of the system -- the galaxies that fall on the observed correlation appear to have reached virial equilibrium. (3) the star formation and black hole growth are self-regulated in galaxies -- the ratio between black hole accretion rate and star formation rate remains nearly constant in a wide redshift span $z = 0-6$. These findings suggest that the observed correlations have different origins: the $\mbhsigma$ relation may be the result of virial equilibrium, while the $\mbhhost$ relation may the result of self-regulated star formation and black hole growth in galaxies.

#### Nov 05, 2012

1211.0013 (/preprints)
2012-11-05, 08:47 

## [1211.0021] Searches for continuous gravitational waves with the LIGO and Virgo detector

Authors: Keith Riles for the LIGO Scientific Collaboration, Virgo Collaboration

Date: 31 Oct 2012

Abstract: The LIGO Scientific Collaboration and Virgo Collaboration have carried out joint searches in LIGO and Virgo data for periodic continuous gravitational waves. These analyses range from targeted searches for gravitational-wave signals from known pulsars, for which precise ephemerides from radio or X-ray observations are used in matched filters, to all-sky searches for unknown neutron stars, including stars in binary systems. Between these extremes lie directed searches for known stars of unknown spin frequency or for new unknown sources at specific locations, such as near the galactic center or in globular clusters. Recent and ongoing searches of each type will be summarized, along with prospects for future searches using data from the Advanced LIGO and Virgo detectors.

#### Nov 05, 2012

1211.0021 (/preprints)
2012-11-05, 08:47 

## [1210.7173] Data analysis challenges in transient gravitational-wave astronomy

Authors: Eric Chassande-Mottin, for the LIGO Scientific Collaboration, for the Virgo Collaboration

Date: 26 Oct 2012

Abstract: Gravitational waves are radiative solutions of space-time dynamics predicted by Einstein's theory of General Relativity. A world-wide array of large-scale and highly-sensitive interferometric detectors constantly scrutinizes the geometry of the local space-time with the hope to detect deviations that would signal an impinging gravitational wave from a remote astrophysical source. Finding the rare and weak signature of gravitational waves buried in non-stationary and non-Gaussian instrument noise is a particularly challenging problem. We will give an overview of the data-analysis techniques and associated observational results obtained so far by Virgo (in Europe) and LIGO (in the US), along with the prospects offered by the up-coming advanced versions of those detectors.

#### Oct 30, 2012

1210.7173 (/preprints)
2012-10-30, 11:46 

## [1210.6983] Fake plunges are very eccentric real EMRIs in disguise ... they dominate the rates and are blissfully ignorant of angular momentum barriers

Authors: Pau Amaro-Seoane, Carlos Sopuerta, Patrick Brem

Date: 25 Oct 2012

Abstract: The capture of a compact object in a galactic nucleus by a massive black hole (MBH) is the best way to map space and time around it. It is well established that the event rate of stars kicked directly through the horizon (referred to as direct plunges) is much larger than the gradual inspiral due to the emission of gravitational waves. We prove that it is actually very difficult to get a compact object such a stellar black hole to be swallowed whole. A plunge will most likely be deflected into an EMRI orbit. They are simply very eccentric EMRIs and dominate the event rate. Moreover, if the central MBH is spinning, the net result on the rates is an enhancement, on both kinds of EMRIs. On the other hand, recent work on stellar dynamics has demonstrated that there seems to be a conspiracy in phase space, since rates decrease significantly by the presence of a blockade in the rate at which orbital angular momenta change takes place. This so-called "Schwarzschild barrier" is a result of the impact of relativistic precession on to the stellar potential torques and was first investigated by Merritt and collaborators. We confirm and quantify the existence of this barrier using a statistical sample of 2,500 direct-summation N-body simulations using both a post-Newtonian but also, and for the first time in a direct-summation integrator, a geodesic approximation for the relativistic orbits. Although the existence of the barrier prevents "traditional EMRIs" (i.e. EMRIs which are not very eccentric) from approaching the central MBH, very eccentric EMRIs, wrongly classified as plunges, insolently ignore the presence of the barrier. The combinations of these effects leads to the result that very eccentric orbits will dominate the rates.

#### Oct 30, 2012

1210.6983 (/preprints)
2012-10-30, 11:45 

## [1210.7293] Creep events and creep noise in gravitational-wave interferometers: basic formalism and stationary limit

Authors: Yuri Levin (Monash University and Leiden Observatory)

Date: 27 Oct 2012

Abstract: In gravitational-wave interferometers, test masses are suspended on thin fibers which experience considerable tension stress. Sudden microscopic stress release in a suspension fiber, which I call a 'creep event', would excite motion of the test mass that would be coupled to the interferometer's readout. The random test-mass motion due to a time-sequence of creep events is referred to as 'creep noise'. In this paper I present an elasto-dynamic calculation for the test-mass motion due to a creep event. I show that within a simple suspension model, the main coupling to the optical readout occurs via a combination of a "dc" horizontal displacement of the test mass, and excitation of the violin and pendulum modes, and not, as was thought previously, via lengthening of the fiber. When the creep events occur sufficiently frequently and their statistics is time-independent, the creep noise can be well-approximated by a stationary Gaussian random process. I derive the functional form of the creep noise spectral density in this limit, with the restrictive assumption that the creep events are statistically independent from each other.

#### Oct 30, 2012

1210.7293 (/preprints)
2012-10-30, 11:44 

## [1210.7518] Prospects for probing strong gravity with a pulsar-black hole system

Authors: N. Wex, K. Liu, R. P. Eatough, M. Kramer, J. M. Cordes, T. J. W. Lazio

Date: 28 Oct 2012

Abstract: The discovery of a pulsar (PSR) in orbit around a black hole (BH) is expected to provide a superb new probe of relativistic gravity and BH properties. Apart from a precise mass measurement for the BH, one could expect a clean verification of the dragging of space-time caused by the BH spin. In order to measure the quadrupole moment of the BH for testing the no-hair theorem of general relativity (GR), one has to hope for a sufficiently massive BH. In this respect, a PSR orbiting the super-massive BH in the center of our Galaxy would be the ultimate laboratory for gravity tests with PSRs. But even for gravity theories that predict the same properties for BHs as GR, a PSR-BH system would constitute an excellent test system, due to the high grade of asymmetry in the strong field properties of these two components. Here we highlight some of the potential gravity tests that one could expect from different PSR-BH systems, utilizing present and future radio telescopes, like FAST and SKA.

#### Oct 30, 2012

1210.7518 (/preprints)
2012-10-30, 11:44 

## [1210.7388] Fifth ASTROD Symposium and Outlook of Direct Gravitational-Wave Detection

Authors: K.G. Arun, Bala R. Iyer, Wei-Tou Ni

Date: 28 Oct 2012

Abstract: From July 11 to July 13, 2012, Raman Research Institute (Bangalore, India) hosted the Fifth International ASTROD Symposium on Laser Astrodynamics, Space Test of Relativity and Gravitational-Wave Astronomy. This is a report on the symposium with an exposition of the outlook of direct gravitational-wave detection.

#### Oct 30, 2012

1210.7388 (/preprints)
2012-10-30, 11:44 

## [1210.6807] Gravitational waveforms for black hole binaries with unequal masses

Authors: M&#xe1;rton T&#xe1;pai, Zolt&#xe1;n Keresztes, L&#xe1;szl&#xf3; &#xc1;rp&#xe1;d Gergely

Date: 25 Oct 2012

Abstract: We derived a post-Newtonian (PN) inspiral only gravitational waveform for unequal mass, spinning black hole binaries. Towards the end of the inspiral the larger spin dominates over the orbital angular momentum (while the smaller spin is negligible), hence the name Spin-Dominated Waveforms (SDW). Such systems are common sources for future gravitational wave detectors and during the inspiral the largest amplitude waves are emitted exactly in its last part. The SDW waveforms emerge as a double expansion in the PN parameter and the ratio of the orbital angular momentum to the dominant spin.

#### Oct 26, 2012

1210.6807 (/preprints)
2012-10-26, 08:31 

## [1210.6666] An effectual template bank for the detection of gravitational waves from inspiralling compact binaries with generic spins

Authors: P. Ajith, N. Fotopoulos, S. Privitera, A. Neunzert, A. J. Weinstein

Date: 24 Oct 2012

Abstract: We report the construction of a three-dimensional template bank for the search for gravitational waves from inspiralling binaries consisting of spinning compact objects. The parameter space consists of two dimensions describing the mass parameters and one "reduced-spin parameter", which describes the secular (non-precessing) spin effects in the waveform. The template placement is based on an efficient stochastic algorithm and makes use of the semi-analytical computation of a metric in the parameter space. We demonstrate that such a template family is "effectual" (effective fitting factor ~ 0.93--0.99) for the detection of generic spinning "low-mass" (m_1 + m_2 <~ 12 M_sun) binaries in the advanced detector era, over the entire parameter space of interest (including binary neutron stars, binary black holes, and black hole-neutron star binaries). This provides a powerful and practical method for searching for gravitational waves from generic spinning low-mass compact binaries. The expected improvement in the average detection volume (at a fixed signal-to-noise-ratio threshold) of this spinning search, as compared to a non-spinning search is ~19--58%.

#### Oct 26, 2012

1210.6666 (/preprints)
2012-10-26, 08:30 

## [1210.6674] General-Relativistic Simulations of Three-Dimensional Core-Collapse Supernovae

Authors: C. D. Ott (1), E. Abdikamalov (1), P. Moesta (1), R. Haas (1), S. Drasco (1,2), E. O&#x27;Connor (3), C. Reisswig (1), C. Meakin (4), E. Schnetter (5) ((1) TAPIR, Caltech, (2) Grinnell College, (3) CITA, (4) Theoretical Division, LANL, (5) Perimeter Institute)

Date: 24 Oct 2012

Abstract: We study the three-dimensional (3D) hydrodynamics of the post-core-bounce phase of the collapse of a 27 solar-mass star and pay special attention to the development of the standing accretion shock instability (SASI) and neutrino-driven convection. To this end, we perform 3D general-relativistic simulations with a 3-species neutrino leakage scheme with neutrino heating. Unlike "light-bulb" heating/cooling schemes, the leakage scheme captures the essential aspects of neutrino cooling, heating, and lepton number exchange as predicted by radiation-hydrodynamics simulations. The 27 solar-mass progenitor was studied in 2D by B. Mueller et al. (2012; arXiv:1205.7078), who observed strong growth of the SASI while neutrino-driven convection was suppressed. In our 3D simulations, neutrino-driven convection grows from numerical perturbations imposed by our Cartesian grid. It becomes the dominant instability and leads to large-scale non-oscillatory deformations of the shock front. These will result in strongly aspherical explosions without the need for large-scale SASI shock oscillations. Low-l-mode SASI oscillations are present in our models, but saturate at small amplitudes that decrease with increasing neutrino heating and vigor of convection. Our results suggest that once neutrino-driven convection is started, it is likely to become the dominant instability in 3D. Whether it is the primary instability after bounce will ultimately depend on the physical seed perturbations present in the cores of massive stars. The gravitational wave signal, which we extract and analyze for the first time from 3D general-relativistic models, will serve as an observational probe of the postbounce dynamics and, in combination with neutrinos, may allow us to determine the primary hydrodynamic instability.

#### Oct 26, 2012

1210.6674 (/preprints)
2012-10-26, 08:30 

## [1210.2396] Resolving multiple supermassive black hole binaries with pulsar timing arrays II: genetic algorithm implementation

Authors: Antoine Petiteau, Stanislav Babak, Alberto Sesana, Mariana de Araujo

Date: 8 Oct 2012

Abstract: Pulsar timing arrays (PTAs) might detect gravitational waves (GWs) from massive black hole (MBH) binaries within this decade. The signal is expected to be an incoherent superposition of several nearly-monochromatic waves of different strength. The brightest sources might be individually resolved, and the overall deconvolved, at least partially, in its individual components. In this paper we extend the maximum-likelihood based method developed in Babak & Sesana 2012, to search for individual MBH binaries in PTA data. We model the signal as a collection of circular monochromatic binaries, each characterized by three free parameters: two angles defining the sky location, and the frequency. We marginalize over all other source parameters and we apply an efficient multi-search genetic algorithm to maximize the likelihood function and look for sources in synthetic datasets. On datasets characterized by white Gaussian noise plus few injected sources with signal-to-noise ratio (SNR) in the range 10-60, our search algorithm performs well, recovering all the injections with no false positives. Individual source SNRs are estimated within few % of the injected values, sky locations are recovered within few degrees, and frequencies are determined with sub-Fourier bin precision.

#### Oct 25, 2012

1210.2396 (/preprints)
2012-10-25, 14:25 

## [1210.6362] Identifying Elusive Electromagnetic Counterparts to Gravitational Wave Mergers: an end-to-end simulation

Authors: Samaya Nissanke, Mansi Kasliwal, Alexandra Georgieva

Date: 23 Oct 2012

Abstract: Combined gravitational-wave (GW) and electromagnetic (EM) observations of compact binary mergers should enable detailed studies of astrophysical processes in the strong-field gravity regime. Networks of GW interferometers have poor angular resolution on the sky and their EM signatures are predicted to be faint. Therefore, a challenging goal will be to unambiguously pinpoint the EM counterparts to GW mergers. We perform the first comprehensive end-to-end simulation that focuses on: i) GW sky localization, distance measures and volume errors with two compact binary populations and four different GW networks, ii) subsequent detectability by a slew of multiwavelength telescopes and, iii) final identification of the merger counterpart amidst a sea of possible astrophysical false-positives. First, we find that double neutron star (NS) binary mergers can be detected out to a maximum distance of 400 Mpc (or 750 Mpc) by three (or five) detector GW networks respectively. NS -- black-hole (BH) mergers can be detected a factor of 1.5 further out. The sky localization uncertainties for NS-BH mergers are 50--170 sq. deg. (or 6--65 sq. deg.) for a three (or five detector) GW network respectively. Second, we quantify relative fractions of optical counterparts that are detectable by different size telescopes. Third, we present five case studies to illustrate the diversity of challenges in secure identification of the EM counterpart at low and high Galactic latitudes. For the first time, we demonstrate how construction of low-latency GW volumes in conjunction with local universe galaxy catalogs can help solve the problem of false positives.

#### Oct 24, 2012

1210.6362 (/preprints)
2012-10-24, 18:55 

## [1210.6014] Weighing The Evidence For A Gravitational-Wave Background In The First International Pulsar Timing Array Data Challenge

Authors: Stephen R. Taylor, Jonathan R. Gair, L. Lentati

Date: 22 Oct 2012

Abstract: We describe an analysis of the First International Pulsar Timing Array Data Challenge. We employ a robust, unbiased Bayesian framework developed by van Haasteren to study the three Open and Closed datasets, testing various models for each dataset and using MultiNest to recover the evidence for the purposes of Bayesian model-selection. The parameter constraints of the favoured model are confirmed using an adaptive MCMC technique. Our results for Closed1 favoured a gravitational-wave background with strain amplitude at f=1 yr-1, A, of (1.1 +/- 0.1) x 10ˆ{-14}, power spectral-index gamma=4.30 +/- 0.15 and no evidence for red-timing noise or single-sources. The evidence for Closed2 favours a gravitational-wave background with A=(6.1 +/- 0.3) x 10ˆ{-14}, gamma=4.34 +/- 0.09 with no red-timing noise or single-sources. Finally, the evidence for Closed3 favours the presence of red-timing noise and a gravitational-wave background, with no single-sources. The properties of the background were A=(5 +/- 1) x 10ˆ{-15} and gamma=4.23 +/- 0.35, while the properties of the red-noise were N_{red}=(12 +/- 4) ns and gamma_{red}=1.5 +/- 0.3. In all cases the redness of the recovered background is consistent with a source-population of inspiraling supermassive black-hole binaries. We also investigate the effect that down-sampling of the datasets has on parameter constraints and run-time. Finally we provide a proof-of-principle study of the ability of the Bayesian framework used in this paper to reconstruct the angular correlation of gravitational-wave background induced timing-residuals, comparing this to the Hellings and Downs curve.

#### Oct 23, 2012

1210.6014 (/preprints)
2012-10-23, 20:15 

## [1210.5998] Why Gravitational Wave Science Needs Pulsar Timing Arrays And Why Pulsar Timing Arrays Need Both Arecibo and the GBT: A Response to the NSF-AST Portfolio Review from the NANOGrav Collaboration

Authors: The NANOGrav Collaboration

Date: 22 Oct 2012

Abstract: Gravitational waves (GWs) are ripples in space-time that are known to exist but have not yet been detected directly. Once they are, a key feature of any viable theory of gravity will be demonstrated and a new window on the Universe opened. GW astronomy was named as one of five key discovery areas in the New Worlds, New Horizons Decadal Report. Pulsar timing probes GW frequencies, and hence source classes, that are inaccessible to any other detection method and can uniquely constrain the nonlinear nature of General Relativity. Pulsar timing is therefore a critical capability with its own discovery space and potential. Fulfilling this capability requires the complementary enabling features of both the Green Bank Telescope (GBT) and the Arecibo Observatory.

#### Oct 23, 2012

1210.5998 (/preprints)
2012-10-23, 20:15 

## [1210.6091] Gravitational wave emission and spindown of young pulsars

Authors: Mark G. Alford, Kai Schwenzer

Date: 23 Oct 2012

Abstract: The rotation frequencies of young pulsars are systematically below their theoretical Kepler limit. R-modes have been suggested as a possible explanation for this observation. With the help of semi-analytic expressions that make it possible to assess the uncertainties of the r-mode scenario due to the impact of uncertainties in underlying microphysics, we perform a quantitative analysis of the the spin-down and the emitted gravitational waves of young pulsars. We find that the frequency to which r-modes spin down a young neutron star as well as the characteristic gravitational wave strain amplitude are extremely insensitive both to the microscopic details and the saturation amplitude. Comparing our result to astrophysical data, we show that for a range of saturation amplitudes r-modes provide a viable spindown scenario and that all observed young pulsars are very likely already outside the r-mode instability region. Taking into account the finite observation time, we find that the signal to noise ratio for gravitational waves is smaller than previous estimates, but large enough to detect such sources with next generation detectors.

#### Oct 23, 2012

1210.6091 (/preprints)
2012-10-23, 19:59 

## [1210.4159] Stellar transits in active galactic nuclei

Authors: Bence B&#xe9;ky, Bence Kocsis (Harvard)

Date: 15 Oct 2012

Abstract: Supermassive black holes (SMBH) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGN) produce a characteristic transit lightcurve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit lightcurves using the Novikov--Thorne thin accretion disk model, including general relatistic effects. Based on the expected properties of stellar cusps, we find that around 10ˆ6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low mass AGNs to 1% photometric accuracy in optical, or ~ 10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit lightcurves could be used to image accretion disks with unprecedented resolution, allowing to resolve the SMBH silhouette in distant AGNs.

#### Oct 17, 2012

1210.4159 (/preprints)
2012-10-17, 12:27 

## [1210.2339] Post-Newtonian prediction for the (2,2) mode of the gravitational wave emitted by compact binaries

Authors: Guillaume Faye, Sylvain Marsat, Luc Blanchet, Bala R. Iyer

Date: 8 Oct 2012

Abstract: We present our 3.5PN computation of the (2,2) mode of the gravitational wave amplitude emitted by compact binaries, on quasi-circular orbits and in the absence of spins. We use the multipolar post-Newtonian wave generation formalism, extending and building on previous works which computed the 3PN order. This calculation required the extension of the multipolar post-Minkowskian algorithm, as well as the computation of the mass source quadrupole at 3.5PN order. Our result will allow more accurate comparisons to numerical relativity, and is a first step towards the computation of the full 3.5PN waveform amplitude, which would improve the estimation of the source parameters by gravitational wave detectors.

#### Oct 15, 2012

1210.2339 (/preprints)
2012-10-15, 22:58 

## [1210.1891] Impact of Higher-order Modes on the Detection of Binary Black Hole Coalescences

Authors: Larne Pekowsky, James Healy, Deirdre Shoemaker, Pablo Laguna

Date: 5 Oct 2012

Abstract: The inspiral and merger of black-hole binary systems are a promising source of gravitational waves. The most effective method to look for a signal with a well understood waveform, such as the binary black hole signal, is matched filtering against a library of model waveforms. Current model waveforms are comprised solely of the dominant radiation mode, the quadrupole mode, although it is known that there can be significant power in the higher-order modes. The binary black hole waveforms produced by numerical relativity are accurate through late inspiral, merger, and ringdown and include the higher-order modes. The available numerical-relativity waveforms span an increasing portion of the physical parameter space of unequal mass, spin and precession. In this paper, we investigate the degree to which gravitational-wave searches could be improved by the inclusion of higher modes in the model waveforms, for signals with a variety of initial mass ratios and generic spins. Our investigation studies how well the quadrupole-only waveform model matches the signal as a function of the inclination and orientation of the source and how the modes contribute to the distance reach into the Universe of Advanced LIGO for a fixed set of internal source parameters. The mismatch between signals and quadrupole-only waveform can be large, dropping below 0.97 for up to 65% of the source-sky for the non-precessing cases we studied, and over a larger area in one precessing case. There is a corresponding 30% increase in detection volume that could be achieved by adding higher modes to the search; however, this is mitigated by the fact that the mismatch is largest for signals which radiate the least energy and to which the search is therefore least sensitive. Likewise, the mismatch is largest in directions from the source along which the least energy is radiated.

#### Oct 15, 2012

1210.1891 (/preprints)
2012-10-15, 22:57 

## [1210.2569] Impact of the second order self-forces on the dephasing of the gravitational waves from quasi-circular extreme mass-ratio inspirals

Authors: Soichiro Isoyama, Ryuichi Fujita, Norichika Sago, Hideyuki Tagoshi, Takahiro Tanaka

Date: 9 Oct 2012

Abstract: The accurate calculation of long-term phase evolution of gravitational wave (GW) forms from extreme (intermediate) mass ratio inspirals (E(I)MRIs) is an inevitable step to extract information from this system. Achieving this goal, it is believed that we need to understand the gravitational self-forces. However, it is not quntatively demonstrated that the second order self-forces are necessary for this purpose. In this paper we revisit the problem to estimate the order of magnitude of the dephasing caused by the second order self-forces on a small body in a quasi-circular orbit around a Kerr black hole, based on the knowledge of the post-Newtonian (PN) approximation and invoking the energy balance argument. In particular, we focus on the averaged dissipative part of the self-force, since it gives the leading order contribution among the various components of them. To avoid the possibility that the energy flux of GWs becomes negative, we propose a new simple resummation called exponential resummation, which assures the positivity of the energy flux. In order to estimate the magnitude of the yet unknown second order self-forces, here we point out the scaling property in the absolute value of the PN coefficients of the energy flux. Using these new tools, we evaluate the expected magnitude of dephasing. Our analysis indicates that the dephasing due to the second order self-forces for quasi-circular E(I)MRIs may be well captured by the 3PN energy flux, once we obtain all the spin dependent terms, except for the case with an extremely large spin of the central Kerr black.

#### Oct 15, 2012

1210.2569 (/preprints)
2012-10-15, 22:56 

## [1210.3007] Suitability of hybrid gravitational waveforms for unequal-mass binaries

Authors: Ilana MacDonald, Abdul H. Mroue, Harald P. Pfeiffer, Michael Boyle, Lawrence E. Kidder, Mark A. Scheel, Bela Szilagyi, Nicholas W. Taylor

Date: 10 Oct 2012

Abstract: This article studies sufficient accuracy criteria of hybrid post-Newtonian (PN) and numerical relativity (NR) waveforms for parameter estimation of strong binary black-hole sources in second- generation ground-based gravitational-wave detectors. We investigate equal-mass non-spinning binaries with a new 33-orbit NR waveform, as well as unequal-mass binaries with mass ratios 2, 3, 4 and 6. For equal masses, the 33-orbit NR waveform allows us to recover previous results and to extend the analysis toward matching at lower frequencies. For unequal masses, the errors between different PN approximants increase with mass ratio. Thus, at 3.5PN, hybrids for higher-mass-ratio systems would require NR waveforms with many more gravitational-wave (GW) cycles to guarantee no adverse impact on parameter estimation. Furthermore, we investigate the potential improvement in hybrid waveforms that can be expected from 4th order post-Newtonian waveforms, and find that knowledge of this 4th post-Newtonian order would significantly improve the accuracy of hybrid waveforms.

#### Oct 15, 2012

1210.3007 (/preprints)
2012-10-15, 22:56 

## [1210.2829] Forecast constraints on cosmic strings from future CMB, pulsar timing and gravitational wave direct detection experiments

Authors: Sachiko Kuroyanagi, Koichi Miyamoto, Toyokazu Sekiguchi, Keitaro Takahashi, Joseph Silk

Date: 10 Oct 2012

Abstract: We study future observational constraints on cosmic string parameters from various types of next-generation experiments: direct detection of gravitational waves (GWs), pulsar timing array, and the cosmic microwave background (CMB). We consider both GW burst and stochastic GW background searches by ground- and space-based interferometers as well as GW background detection in pulsar timing experiments. We also consider cosmic string contributions to the CMB temperature and polarization anisotropies. These different types of observations offer independent probes of cosmic strings and may enable us to investigate cosmic string properties if the signature is detected. In this paper, we evaluate the power of future experiments to constrain cosmic string parameters, such as the string tension Gmu, the initial loop size alpha, and the reconnection probability p, by performing Fisher information matrix calculations. We find that combining the information from the different types of observations breaks parameter degeneracies and provides more stringent constraints on the parameters. We also find future space-borne interferometers independently provide a highly precise determination of the parameters.

#### Oct 15, 2012

1210.2829 (/preprints)
2012-10-15, 22:55 

## [1210.2745] The classical mechanics of non-conservative systems

Date: 9 Oct 2012

Abstract: Hamilton's principle of stationary action lies at the foundation of theoretical physics and is applied in many other disciplines from pure mathematics to economics. Despite its utility, Hamilton's principle has a subtle pitfall that often goes unnoticed in physics: it is formulated as a boundary value problem in time but is used to derive equations of motion that are solved with initial data. This subtlety can have undesirable effects. I present a formulation of Hamilton's principle that is compatible with initial value problems. Remarkably, this leads to a natural formulation for the Lagrangian and Hamiltonian dynamics of generic non-conservative systems, thereby filling a long-standing gap in classical mechanics. Thus dissipative effects, for example, can be studied with new tools that may have application in a variety of disciplines. The new formalism is demonstrated by two examples of non-conservative systems: an object moving in a fluid with viscous drag forces and a harmonic oscillator coupled to a dissipative environment.

#### Oct 15, 2012

1210.2745 (/preprints)
2012-10-15, 22:55 

## [1210.2834] Gravitational radiation reaction along general orbits in the effective one-body formalism

Authors: Donato Bini, Thibault Damour

Date: 10 Oct 2012

Abstract: We derive the gravitational radiation-reaction force modifying the Effective One Body (EOB) description of the conservative dynamics of binary systems. Our result is applicable to general orbits (elliptic or hyperbolic) and keeps terms of fractional second post-Newtonian order (but does not include tail effects). Our derivation of radiation-reaction is based on a new way of requiring energy and angular momentum balance. We give several applications of our results, notably the value of the (minimal) "Schott" contribution to the energy, the radial component of the radiation-reaction force, and the radiative contribution to the angle of scattering during hyperbolic encounters. We present also new results about the conservative relativistic dynamics of hyperbolic motions.

#### Oct 15, 2012

1210.2834 (/preprints)
2012-10-15, 22:55 

## [1210.3095] Outlook for detection of GW inspirals by GRB-triggered searches in the advanced detector era

Authors: Alexander Dietz, Nickolas Fotopoulos, Leo Singer, Curt Cutler

Date: 11 Oct 2012

Abstract: Short GRBs are believed to originate from the coalescence of two NSs or a NS and a BH. If this scenario is correct, short GRBs will be accompanied by the emission of strong GWs, detectable by GW observatories such as LIGO and Virgo. As compared with blind, all-sky, all-time GW searches, externally triggered searches for GW counterparts to short GRBs have the advantages of both significantly reduced detection threshold due to known time and sky location and preferentially higher GW amplitude because of face-on orientation. Based on the distribution of SNR in candidate CBC events in the most recent joint LIGO--Virgo data, we find an effective sensitive volume for GRB-triggered searches that ~2 times greater than for blind searches. For NSNS systems, a jet angle of 20 degrees, and an effective gamma-ray satellite field-of-view of 10% of the sky, this doubles the number of NSNS--short GRB associations to 4% of all NSNS detections. We also investigate the power of tests for statistical excesses in lists of sub-threshold events, and show that these are unlikely to reveal a sub-threshold population until finding individual sources is already routine.

#### Oct 15, 2012

1210.3095 (/preprints)
2012-10-15, 22:54 

## [1210.2778] Observing the Galaxy's massive black hole with gravitational wave bursts

Authors: C. P. L. Berry, J. R. Gair

Date: 9 Oct 2012

Abstract: An extreme-mass-ratio burst (EMRB) is a gravitational wave signal emitted when a compact object passes through periapsis on a highly eccentric orbit about a much more massive object, in our case a stellar mass object about a 10ˆ6 M_sol black hole. EMRBs are a relatively unexplored means of probing the spacetime of massive black holes (MBHs). We conduct an investigation of the properties of EMRBs and how they could allow us to constrain the parameters, such as spin, of the Galaxy's MBH. We find that if an EMRB event occurs in the Galaxy, it should be detectable for periapse distances r_p < 65 r_g for a \mu = 10 M_sol orbiting object, where r_g = GM/cˆ2 is the gravitational radius. The signal-to-noise ratio scales as \rho ~ -2.7 log(r_p/r_g) + log(\mu/M_sol) + 4.9. For periapses r_p < 10 r_g, EMRBs can be informative, and provide good constraints on both the MBH's mass and spin. Closer orbits provide better constraints, with the best giving accuracies of better than one part in 10ˆ4 for both the mass and spin parameter.

#### Oct 15, 2012

1210.2778 (/preprints)
2012-10-15, 22:54 

## [1210.3374] Consequences of Strong Compression in Tidal Disruption Events

Authors: Nicholas Stone, Re&#x27;em Sari, Abraham Loeb

Date: 11 Oct 2012

Abstract: The tidal disruption of a star by a supermassive black hole (SMBH) is a highly energetic event with consequences dependent on the degree to which the star plunges inside the SMBH's tidal sphere. We introduce a new analytic model for tidal disruption events (TDEs) to analyze the dependence of these events on beta, the ratio of the tidal radius to the orbital pericenter. We find, contrary to most previous work, that the spread in debris energy for a TDE is largely constant for all beta. This result has important consequences for optical transient searches targeting TDEs, which we discuss. We quantify leading-order general relativistic corrections to this spread in energy and find that they are small. We also examine the role of stellar spin, and find that a combination of spin-orbit misalignment, rapid rotation, and high beta may increase the spread in debris energy. Finally, we quantify for the first time the gravitational wave emission due to the strong compression of a star in a high-beta TDE. Although this signal is unlikely to be detectable for disruptions of main sequence stars, the tidal disruption of a white dwarf by an intermediate mass black hole can produce a strong signal visible to Advanced LIGO at tens of megaparsecs.

#### Oct 15, 2012

1210.3374 (/preprints)
2012-10-15, 22:53 

## [1210.3489] Using Swarm Intelligence To Accelerate Pulsar Timing Analysis

Authors: Stephen R. Taylor, Jonathan R. Gair, L. Lentati

Date: 12 Oct 2012

Abstract: We provide brief notes on a particle swarm-optimisation approach to constraining the properties of a stochastic gravitational-wave background in the first International Pulsar Timing Array data-challenge. The technique employs many computational-agents which explore parameter space, remembering their most optimal positions and also sharing this information with all other agents. It is this sharing of information which accelerates the convergence of all agents to the global best-fit location in a very short number of iterations. Error estimates can also be provided by fitting a multivariate Gaussian to the recorded fitness of all visited points.

#### Oct 15, 2012

1210.3489 (/preprints)
2012-10-15, 22:53 

## [1210.3402] Constraining the High-Density Behavior of Nuclear Symmetry Energy with the Tidal Polarizability of Neutron Stars

Authors: F. J. Fattoyev, J. Carvajal, W. G. Newton, Bao-An Li

Date: 12 Oct 2012

Abstract: Using a set of model equations of state satisfying the latest constraints from both terrestrial nuclear experiments and astrophysical observations as well as state-of-the-art nuclear many-body calculations of the pure neutron matter equation of state, the tidal polarizability of canonical neutron stars in coalescing binaries is found to be a very sensitive probe of the high-density behavior of nuclear symmetry energy which is among the most uncertain properties of dense neutron-rich nucleonic matter. Moreover, it changes less than $\pm 10%$ by varying various properties of symmetric nuclear matter and symmetry energy around the saturation density within their respective ranges of remaining uncertainty.

#### Oct 15, 2012

1210.3402 (/preprints)
2012-10-15, 22:53 

## [1210.3770] Can we see pulsars around Sgr A*? - The latest searches with the Effelsberg telescope

Authors: R. P. Eatough, M. Kramer, B. Klein, R. Karuppusamy, D. J. Champion, P. C. C. Freire, N. Wex, K. Liu

Date: 14 Oct 2012

Abstract: Radio pulsars in relativistic binary systems are unique tools to study the curved space-time around massive compact objects. The discovery of a pulsar closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr A*, would provide a superb test-bed for gravitational physics. To date, the absence of any radio pulsar discoveries within a few arc minutes of Sgr A* has been explained by one principal factor: extreme scattering of radio waves caused by inhomogeneities in the ionized component of the interstellar medium in the central 100 pc around Sgr A*. Scattering, which causes temporal broadening of pulses, can only be mitigated by observing at higher frequencies. Here we describe recent searches of the Galactic centre region performed at a frequency of 18.95 GHz with the Effelsberg radio telescope.

#### Oct 15, 2012

1210.3770 (/preprints)
2012-10-15, 22:33 

## [1210.4143] Next-to-next-to-leading order spin-orbit effects in the equations of motion of compact binary systems

Authors: Sylvain Marsat, Alejandro Bohe, Guillaume Faye, Luc Blanchet

Date: 15 Oct 2012

Abstract: We compute next-to-next-to-leading order spin contributions to the post-Newtonian equations of motion for binaries of compact objects, such as black holes or neutron stars. For maximally spinning black holes, those contributions are of third-and-a-half post-Newtonian (3.5PN) order, improving our knowledge of the equations of motion, already known for non-spinning objects up to this order. Building on previous work, we represent the rotation of the two bodies using a pole-dipole matter stress-energy tensor, and iterate Einstein's field equations for a set of potentials parametrizing the metric in harmonic coordinates. Checks of the result include the existence of a conserved energy, the approximate global Lorentz invariance of the equations of motion in harmonic coordinates, and the recovery of the motion of a spinning object on a Kerr background in the test-mass limit. We verified the existence of a contact transformation, together with a redefinition of the spin variables that makes our result equivalent to a previously published reduced Hamiltonian, obtained from the Arnowitt-Deser-Misner (ADM) formalism.

#### Oct 15, 2012

1210.4143 (/preprints)
2012-10-15, 22:33 

## [1210.3854] Does a 'stochastic' background of gravitational waves exist in the pulsar timing band?

Authors: V. Ravi, J. S. B. Wyithe, G. Hobbs, R. M. Shannon, R. N. Manchester, D. R. B. Yardley, M. J. Keith

Date: 14 Oct 2012

Abstract: We investigate the effects of gravitational waves (GWs) from a simulated population of binary super-massive black holes (SMBHs) on pulsar timing array datasets. We construct a distribution describing the binary SMBH population from an existing semi-analytic galaxy formation model. Using realizations of the binary SMBH population generated from this distribution, we simulate pulsar timing datasets with GW-induced variations. We find that the statistics of these variations do not correspond to an isotropic, stochastic GW background. The "Hellings & Downs" correlations between simulated datasets for different pulsars are recovered on average, though the scatter of the correlation estimates is greater than expected for an isotropic, stochastic GW background. These results are attributable to the fact that just a few GW sources dominate the GW-induced variations in every Fourier frequency bin of a 5-year dataset. Current constraints on the amplitude of the GW signal from binary SMBHs will be biased. Individual binary systems are likely to be detectable in 5-year pulsar timing array datasets where the noise is dominated by GW-induced variations. Searches for GWs in pulsar timing array data therefore need to account for the effects of individual sources of GWs.

#### Oct 15, 2012

1210.3854 (/preprints)
2012-10-15, 22:32 

## [1210.1294] The Shortest Known Period Star Orbiting our Galaxy's Supermassive Black Hole

Authors: L. Meyer, A. M. Ghez, R. Schoedel, S. Yelda, A. Boehle, J. R. Lu, T. Do, M. R. Morris, E. E. Becklin, K. Matthews

Date: 4 Oct 2012

Abstract: Stars with short orbital periods at the center of our galaxy offer a powerful and unique probe of a supermassive black hole. Over the past 17 years, the W. M. Keck Observatory has been used to image the Galactic center at the highest angular resolution possible today. By adding to this data set and advancing methodologies, we have detected S0-102, a star orbiting our galaxy's supermassive black hole with a period of just 11.5 years. S0-102 doubles the number of stars with full phase coverage and periods less than 20 years. It thereby provides the opportunity with future measurements to resolve degeneracies in the parameters describing the central gravitational potential and to test Einstein's theory of General Relativity in an unexplored regime.

#### Oct 04, 2012

1210.1294 (/preprints)
2012-10-04, 19:07 

## [1210.1333] Finite, Intense Accretion Bursts from Tidal Disruption of Stars on Bound Orbits

Authors: Kimitake Hayasaki, Nicholas Stone, Abraham Loeb

Date: 4 Oct 2012

Abstract: We study accretion processes for tidally disrupted stars approaching supermassive black holes on bound orbits, by performing three dimensional Smoothed Particle Hydrodynamics simulations with a pseudo-Newtonian potential. We find that there is a critical value of the orbital eccentricity below which all the stellar debris remains bound to the black hole. For high but sub-critical eccentricities, all the stellar mass is accreted onto the black hole in a finite time, causing a significant deviation from the canonical $tˆ{-5/3}$ mass fallback rate. When a star is on a moderately eccentric orbit and its pericenter distance is deeply inside the tidal disruption radius, there can be several orbit crossings of the debris streams due to relativistic precession. This dissipates orbital energy in shocks, allowing for rapid circularization of the debris streams and formation of an accretion disk. The resultant accretion rate greatly exceeds the Eddington rate and differs strongly from the canonical rate of $tˆ{-5/3}$. By contrast, there is little dissipation due to orbital crossings for the equivalent simulation with a purely Newtonian potential. This shows that general relativistic precession is crucial for accretion disk formation via circularization of stellar debris from stars on moderately eccentric orbits.

#### Oct 04, 2012

1210.1333 (/preprints)
2012-10-04, 18:36 

## [1210.1214] The runaway instability in general-relativistic accretion disks

Authors: O. Korobkin (1), E. Abdikamalov (2), N. Stergioulas (3), E. Schnetter (4), B. Zink (5), S. Rosswog (1), C. Ott (2) ((1) Stockholm University, (2) Caltech, (3) Thessaloniki, (4) Perimeter Institute, (5) University of T&#xfc;bingen)

Date: 3 Oct 2012

Abstract: When an accretion disk falls prey to the runaway instability, a large portion of its mass is devoured by the black hole within a few dynamical times. Despite decades of effort, it is still unclear under what conditions such an instability can occur. The technically most advanced relativistic simulations to date were unable to find a clear sign for the onset of the instability. In this work, we present three-dimensional relativistic hydrodynamics simulations of accretion disks around black holes in dynamical spacetime. We focus on the configurations that are expected to be particularly prone to the development of this instability. We demonstrate, for the first time, that the fully self-consistent general relativistic evolution does indeed produce a runaway instability.

#### Oct 04, 2012

1210.1214 (/preprints)
2012-10-04, 18:36 

## [1210.0577] Two-step greedy algorithm for reduced order quadratures

Authors: Harbir Antil, Scott E. Field, Frank Herrmann, Ricardo H. Nochetto, Manuel Tiglio

Date: 1 Oct 2012

Abstract: We present an algorithm to generate application-specific, global reduced order quadratures (ROQ) for multiple fast evaluations of weighted inner products between parameterized functions. If a reduced basis (RB) or any other projection-based model reduction technique is applied, the dimensionality of integrands is reduced dramatically; however, the cost of evaluating the reduced integrals still scales as the size of the original problem. In contrast, using discrete empirical interpolation (DEIM) points as ROQ nodes leads to a computational cost which depends linearly on the dimension of the reduced space. Generation of a reduced basis via a greedy procedure requires a training set, which for products of functions can be very large. Since this direct approach can be impractical in many applications, we propose instead a two-step greedy targeted towards approximation of such products. We present numerical experiments demonstrating the accuracy and the efficiency of the two-step approach. The presented ROQ are expected to display very fast convergence whenever there is regularity with respect to parameter variation. We find that for the particular application here considered, one driven by gravitational wave physics, the two-step approach speeds up the offline computations to build the ROQ by more than two orders of magnitude. Furthermore, the resulting ROQ rule converges exponentially with the number of nodes, and a factor of ~50 savings, without loss of accuracy, is observed in evaluations of inner products when ROQ are used as a downsampling strategy for equidistant samples using the trapezoidal rule. While the primary focus of this paper is on quadrature rules for inner products of parameterized functions, our method can be easily adapted to integrations of single parameterized functions, and some examples of this type are also considered.

#### Oct 04, 2012

1210.0577 (/preprints)
2012-10-04, 18:35 

## [1210.0901] Two stellar-mass black holes in the globular cluster M22

Authors: Jay Strader (Michigan State), Laura Chomiuk (NRAO/Michigan State), Thomas Maccarone (Southampton), James Miller-Jones (ICRAR-Curtin), Anil Seth (Utah)

Date: 2 Oct 2012

Abstract: Hundreds of stellar-mass black holes likely form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star ("black-hole/X-ray binaries") in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known. Although a few black holes have been seen in globular clusters around other galaxies, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each ~ 10-20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside. The identification of two black holes in one cluster shows that the ejection of black holes is not as efficient as predicted by most models, and we argue that M22 may contain a total population of ~ 5-100 black holes. The large core radius of M22 could arise from heating produced by the black holes.

#### Oct 04, 2012

1210.0901 (/preprints)
2012-10-04, 09:29 

## [1210.0764] Third post-Newtonian spin-orbit effect in the gravitational radiation flux of compact binaries

Authors: Luc Blanchet, Alessandra Buonanno, Guillaume Faye

Date: 2 Oct 2012

Abstract: Gravitational waves contain tail effects that are due to the backscattering of linear waves in the curved space-time geometry around the source. The knowledge as well as the accuracy of the two-body inspiraling post-Newtonian (PN) dynamics and of the gravitational-wave signal has been recently improved, notably by computing the spin-orbit (SO) terms induced by tail effects in the gravitational-wave energy flux at the 3PN order. Here we sketch this derivation, which yields the phasing formula including SO tail effects through the same 3PN order. Those results can be employed to improve the accuracy of analytical templates aimed at describing the whole process of inspiral, merger, and ringdown.

#### Oct 03, 2012

1210.0764 (/preprints)
2012-10-03, 09:47 

## [1210.0893] Systematic biases in parameter estimation of binary black-hole mergers

Authors: Tyson B. Littenberg, John G. Baker, Alessandra Buonanno, Bernard J. Kelly

Date: 2 Oct 2012

Abstract: Parameter estimation of binary-black-hole merger events in gravitational-wave data relies on matched-filtering techniques, which, in turn, depend on accurate model waveforms. Here we characterize the systematic biases introduced in measuring astrophysical parameters of binary black holes by applying the currently most accurate effective-one-body templates to simulated data containing non-spinning numerical-relativity waveforms. For advanced ground-based detectors, we find that the systematic biases are well within the statistical error for realistic signal-to-noise ratio (SNR). These biases grow to be comparable to the statistical errors at high ground-based-instrument SNRs (SNR=50), but never dominate the error budget. At the much larger signal-to-noise ratios expected for space-based detectors, these biases will become large compared to the statistical errors, but for astrophysical black hole mass estimates the absolute biases (of at most a few percent) are still fairly small.

#### Oct 03, 2012

1210.0893 (/preprints)
2012-10-03, 09:47 

## [1210.0584] Accelerating pulsar timing data analysis

Authors: Rutger van Haasteren (AEI Hannover)

Date: 1 Oct 2012

Abstract: The analysis of pulsar timing data, especially in pulsar timing array (PTA) projects, has encountered practical difficulties: evaluating the likelihood and/or correlation-based statistics can become prohibitively computationally expensive for large datasets. In situations where a stochastic signal of interest has a power spectral density that dominates the noise in a limited bandwidth of the total frequency domain (e.g. the isotropic background of gravitational waves), a linear transformation exists that transforms the timing residuals to a basis in which virtually all the information about the stochastic signal of interest is contained in a small fraction of basis vectors. By only considering such a small subset of these "generalised residuals", the dimensionality of the data analysis problem is greatly reduced, which can cause a large speedup in the evaluation of the likelihood: the ABC-method (Acceleration By Compression). The compression fidelity, calculable with crude estimates of the signal and noise, can be used to determine how far a dataset can be compressed without significant loss of information. Both direct tests on the likelihood, and Bayesian analysis of mock data, show that the signal can be recovered as well as with an analysis of uncompressed data. In the analysis of IPTA Mock Data Challenge datasets, speedups of a factor of three orders of magnitude are demonstrated. For realistic PTA datasets the acceleration may become greater than six orders of magnitude due to the low signal to noise ratio.

#### Oct 03, 2012

1210.0584 (/preprints)
2012-10-03, 09:46 

## [1210.0483] A Metric for Testing the Nature of Black Holes

Authors: Tim Johannsen (Waterloo, Perimeter, Arizona)

Date: 1 Oct 2012

Abstract: In general relativity, astrophysical black holes are uniquely described by the Kerr metric. Observational tests of the Kerr nature of these compact objects and, hence, of general relativity, require a metric that encompasses a broader class of black holes as possible alternatives to the usual Kerr black holes. Several such Kerr-like metrics have been constructed to date, which depend on a set of free parameters and which reduce smoothly to the Kerr metric if all deviations vanish. Many of these metrics, however, are valid only for small values of the spin or small perturbations of the Kerr metric or contain regions of space where they are unphysical hampering their ability to properly model the accretions flows of black holes. In this paper, I describe a Kerr-like black hole metric that is regular everywhere outside of the event horizon for black holes with arbitrary spins even for large deviations from the Kerr metric. This metric, therefore, provides an ideal framework for tests of the nature of black holes with observations of the emission from their accretion flows, and I give several examples of such tests across the electromagnetic spectrum with current and near-future instruments.

#### Oct 01, 2012

1210.0483 (/preprints)
2012-10-01, 18:16 

## [1210.0224] PSR J1141-6545: a powerful laboratory of GR and tensor-scalar theories of gravity

Authors: J. P. W. Verbiest, N. D. R. Bhat, M. Bailes

Date: 30 Sep 2012

Abstract: Pulsars in close binary systems have provided some of the most stringent tests of strong-field gravity to date. The pulsar--white-dwarf binary system J1141-6545 is specifically interesting due to its gravitational asymmetry which makes it one of the most powerful probes of tensor-scalar theories of gravity. We give an overview of current gravitational tests provided by the J1141-6545 binary system and comment on how anomalous accelerations, geodetic precession and timing instabilities may be prevented from limiting future tests of gravity to come from this system.

#### Oct 01, 2012

1210.0224 (/preprints)
2012-10-01, 18:15 

## [1210.0201] The Effective Field Theory of Dark Energy

Authors: Giulia Gubitosi, Federico Piazza, Filippo Vernizzi

Date: 30 Sep 2012

Abstract: We propose a universal description of dark energy and modified gravity that includes all single-field models. By extending a formalism previously applied to inflation, we consider the metric universally coupled to matter fields and we write in terms of it the most general unitary gauge action consistent with the residual unbroken symmetries of spatial diffeomorphisms. Our action is particularly suited for cosmological perturbation theory: the background evolution depends on only three operators. All other operators start at least at quadratic order in the perturbations and their effects can be studied independently and systematically. In particular, we focus on the properties of a few operators which appear in non-minimally coupled scalar-tensor gravity and galileon theories. In this context, we study the mixing between gravity and the scalar degree of freedom. We assess the quantum and classical stability, derive the speed of sound of fluctuations and the renormalization of the Newton constant. The scalar can always be de-mixed from gravity at quadratic order in the perturbations, but not necessarily through a conformal rescaling of the metric. We show how to express covariant field-operators in our formalism and give several explicit examples of dark energy and modified gravity models in our language. Finally, we discuss the relation with the covariant EFT methods recently appeared in the literature.

#### Oct 01, 2012

1210.0201 (/preprints)
2012-10-01, 18:15 

## [1210.0443] Ultrarelativistic black hole formation

Authors: William E. East, Frans Pretorius

Date: 1 Oct 2012

Abstract: We study the ultrarelativistic head-on collision of equal mass particles, modeled as self-gravitating fluid spheres, by numerically solving the coupled Einstein-hydrodynamic equations. We focus on cases well within the kinetic energy dominated regime, where between 88-92% ($\gamma=8$ to 12) of the initial net energy of the spacetime resides in the translation kinetic energy of the particles. We find that for sufficiently large boosts, black hole formation occurs. Moreover, near yet above the threshold of black hole formation, the collision initially leads to the formation of two distinct apparent horizons that subsequently merge. We argue that this can be understood in terms of a focusing effect, where one boosted particle acts as a gravitational lens on the other and vice versa, and that this is further responsible for the threshold being lower (by a factor of a few) compared to simple hoop conjecture estimates. Cases slightly below threshold result in complete disruption of the model particles. The gravitational radiation emitted when black holes form reaches luminosities of 0.014 $cˆ5/G$, carrying $16\pm2%$ of the total energy.

#### Oct 01, 2012

1210.0443 (/preprints)
2012-10-01, 18:15 

## [1210.0156] Probing the strong gravity regime with eLISA: Progress on EMRIs

Authors: Carlos F. Sopuerta (ICE (CSIC-IEEC))

Date: 29 Sep 2012

Abstract: The capture of a stellar-mass compact object by a supermassive black hole and the subsequent inspiral (driven by gravitational radiation emission) constitute one of the most important sources of gravitational waves for space-based observatories like eLISA/NGO. In this article we describe their potential as high-precision tools that can be used to perform tests of the geometry of black holes and also of the strong field regime of gravity.

#### Oct 01, 2012

1210.0156 (/preprints)
2012-10-01, 18:15 

## [1209.6428] Applying Bayesian Inference to the first International Pulsar Timing Array data challenge

Authors: Neil J. Cornish

Date: 28 Sep 2012

Abstract: This is a very brief summary of the techniques I used to analyze the IPTA challenge 1 data sets. I tried many things, and more failed than succeeded, but in the end I found two approaches that appear to work based on tests done using the open data sets. One approach works directly with the time domain data, and the other works with a specially constructed Fourier transform of the data. The raw data was run through TEMPO2 to produce reduced timing residuals for the analysis. Standard Markov Chain Monte Carlo techniques were used to produce samples from the posterior distribution function for the model parameters. The model parameters include the gravitational wave amplitude and spectral slope, and the white noise amplitude for each pulsar in the array. While red timing noise was only included in Dataset 3, I found that it was necessary to include effective red noise in all the analyses to account for some of the spurious effects introduced by the TEMPO2 timing fit. This added an additional amplitude and slope parameter for each pulsar, so my overall model for the 36 pulsars residuals has 110 parameters. As an alternative to using an effective red noise model, I also tried to simultaneously re-fit the timing model model while looking for the gravitational wave signal, but for reasons that are not yet clear, this approach was not very successful. I comment briefly on ways in which the algorithms could be improved. My best estimates for the gravitational wave amplitudes in the three closed (blind) data sets are: (1) $A=(7.3\pm 1.0)\times 10ˆ{-15}$; (2) $A=(5.7\pm 0.6)\times 10ˆ{-14}$; and (3) $A=(4.6\pm 1.3)\times 10ˆ{-15}$.

#### Oct 01, 2012

1209.6428 (/preprints)
2012-10-01, 13:35 

## [1209.5171] New Constraints on Preferred Frame Effects from Binary Pulsars

Authors: Lijing Shao, Norbert Wex, Michael Kramer

Date: 24 Sep 2012

Abstract: Preferred frame effects (PFEs) are predicted by a number of alternative gravity theories which include vector or additional tensor fields, besides the canonical metric tensor. In the framework of parametrized post-Newtonian (PPN) formalism, we investigate PFEs in the orbital dynamics of binary pulsars, characterized by the two strong-field PPN parameters, \alpha_1 and \alpha_2. In the limit of a small orbital eccentricity, \alpha_1 and \alpha_2 contributions decouple. By utilizing recent radio timing results and optical observations of PSRs J1012+5307 and J1738+0333, we obtained the best limits of \alpha_1 and \alpha_2 in the strong-field regime. The constraint on \alpha_1 also surpasses its counterpart in the weak-field regime.

#### Sep 28, 2012

1209.5171 (/preprints)
2012-09-28, 09:54 

## [1209.5308] Gravitational waves from the evolution of the f-mode instability in neutron stars

Authors: A. Passamonti, E. Gaertig, K. Kokkotas

Date: 24 Sep 2012

Abstract: We study the dynamical evolution of the gravitational-wave driven instability of the f-mode in rapidly rotating relativistic stars. With an approach based on linear perturbation theory we describe the evolution of the mode amplitude and follow the trajectory of a newborn neutron star through its instability window. The influence on the f-mode instability of the magnetic field and the presence of an unstable r-mode is also considered. Two different configurations are studied in more detail; a standard N = 1 polytrope with a typical mass and radius and a more extreme polytropic N = 2/3 model which describes a supramassive neutron star. We study several evolutions with different initial rotation rates and temperature and determine the gravitational waves radiated during the instability. For reasonable values of the mode saturation amplitude, i.e. with a mode energy of about 1e6 Msun cˆ2, the gravitational-wave signal can be detected by the Einstein Telescope detector from the Virgo cluster. The magnetic field affects the evolution and then the detectability of the gravitational radiation when its strength is higher than 1e12 G, while the effects of an unstable r-mode become dominant when this mode reaches the maximum saturation value allowed by non-linear mode couplings. However, the relative saturation amplitude of the f- and r-modes must be known more accurately in order to provide a definitive answer to this issue. From the thermal evolution we find also that the heat generated by shear viscosity during the saturation phase completely balances the neutrino cooling and prevents the star from entering the regime of mutual friction. The evolution time of the instability is therefore longer and the star loses significantly larger amounts of angular momentum via gravitational waves.

#### Sep 28, 2012

1209.5308 (/preprints)
2012-09-28, 09:54 

## [1209.5731] Extreme-mass-ratio bursts from the Galactic Centre

Authors: Christopher P. L. Berry, Jonathan R. Gair

Date: 25 Sep 2012

Abstract: An extreme-mass-ratio burst (EMRB) is a gravitational wave signal emitted when a compact object passes through periapsis on a highly eccentric orbit about a much more massive body, in our case a stellar mass object about the 4.31 \times 10ˆ6 M_sol massive black hole (MBH) in the Galactic Centre. We investigate how EMRBs could constrain the parameters of the Galaxy's MBH. EMRBs should be detectable if the periapsis is r_p < 65 r_g for a \mu = 10 M_sol orbiting object, where r_g = GM/cˆ2 is the gravitational radius. The signal-to-noise ratio \rho scales like log(\rho) = -2.7 log(r_p/r_g) + log(\mu/M_sol) + 4.9. For periapses smaller than ~ 10 r_g, EMRBs can be informative, providing good constraints on both the MBH's mass and spin.

#### Sep 28, 2012

1209.5731 (/preprints)
2012-09-28, 09:53 

## [1209.5747] Ultra-Relativistic Counterparts to Binary Neutron Star Mergers in Every Direction, X-ray-to-Radio Bands and Second-to-Day Timescales

Authors: Koutarou Kyutoku, Kunihito Ioka, Masaru Shibata

Date: 25 Sep 2012

Abstract: We propose a possibility of ultra-relativistic electromagnetic counterparts to gravitational waves from binary neutron star mergers at any viewing angle. Mechanisms include the merger-shock propagation accelerating a smaller fraction of the neutron star surface to larger Lorentz factor, with the outer parts carrying less energy, ~10ˆ{47} \Gammaˆ{-1} erg. This mechanism is difficult to resolve by current 3D numerical simulations, and depends on the neutron star equation of state. The outflows emit synchrotron flares for seconds to days by shocking the surrounding medium. Ultra-relativistic flares shine at early times and high energies, potentially detectable by current X-ray to radio instruments, such as Swift XRT and Pan-STARRS, and even in low ambient density ~10ˆ{-2} cmˆ{-3} by EVLA. The flares probe the merger position and time, and the merger types as black hole-neutron star outflows would be non/mildly-relativistic.

#### Sep 28, 2012

1209.5747 (/preprints)
2012-09-28, 09:52 

## [1209.6286] Astrophysical Model Selection in Gravitational Wave Astronomy

Authors: Matthew Adams, Neil Cornish, Tyson Littenberg

Date: 27 Sep 2012

Abstract: Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a Hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space based gravitational wave detector. We find that a mission that is able to resolve ~5000 of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.

#### Sep 28, 2012

1209.6286 (/preprints)
2012-09-28, 09:48 

## [1209.6349] Spin effects on gravitational waves from inspiraling compact binaries at second post-Newtonian order

Authors: Alessandra Buonanno, Guillaume Faye, Tanja Hinderer

Date: 27 Sep 2012

Abstract: We calculate the gravitational waveform for spinning, precessing compact binary inspirals through second post-Newtonian order in the amplitude. When spins are collinear with the orbital angular momentum and the orbits are quasi-circular, we further provide explicit expressions for the gravitational-wave polarizations and the decomposition into spin-weighted spherical-harmonic modes. Knowledge of the second post-Newtonian spin terms in the waveform could be used to improve the physical content of analytical templates for data analysis of compact binary inspirals and for more accurate comparisons with numerical-relativity simulations.

#### Sep 28, 2012

1209.6349 (/preprints)
2012-09-28, 09:48 

## [1209.6148] An all-purpose metric for the exterior of any kind of rotating neutron star

Authors: George Pappas, Theocharis A. Apostolatos

Date: 27 Sep 2012

Abstract: We have tested the appropriateness of two-soliton analytic metric to describe the exterior of all types of neutron stars, no matter what their equation of state or rotation rate is. The particular analytic solution of the vaccuum Einstein equations proved quite adjustable to mimic the metric functions of all numerically constructed neutron-star models that we used as a testbed. The neutron-star models covered a wide range of stiffness, with regard to the equation of state of their interior, and all rotation rates up to the maximum possible rotation rate allowed for each such star. Apart of the metric functions themselves, we have compared the radius of the innermost stable circular orbit $R_{\rm{ISCO}}$, the orbital frequency $\Omega\equiv\frac{d\phi}{dt}$ of circular geodesics, and their epicyclic frequencies $\Omega_{\rho}, \Omega_z$, as well as the change of the energy of circular orbits per logarithmic change of orbital frequency $\Delta\tilde{E}$. All these quantities, calculated by means of the two-soliton analytic metric, fitted with good accuracy the corresponding numerical ones as in previous analogous comparisons (although previous attempts were restricted to neutron star models with either high or low rotation rates). We believe that this particular analytic solution could be considered as an analytic faithful representation of the gravitation field of any rotating neutron star with such accuracy, that one could explore the interior structure of a neutron star by using this space-time to interpret observations of astrophysical processes that take place around it.

#### Sep 28, 2012

1209.6148 (/preprints)
2012-09-28, 09:47 

## [1209.0761] Total Angular Momentum Waves for Scalar, Vector, and Tensor Fields

Authors: Liang Dai, Marc Kamionkowski, Donghui Jeong

Date: 4 Sep 2012

Abstract: Most calculations in cosmological perturbation theorydecompose those perturbations into plane waves (Fourier modes). However, for some calculations, particularly those involving observations performed on a spherical sky, a decomposition into waves of fixed total angular momentum (TAM) may be more appropriate. Here we introduce TAM waves, solutions of fixed total angular momentum to the Helmholtz equation, for three-dimensional scalar, vector, and tensor fields. The vector TAM waves of given total angular momentum can be decomposed further into a set of three basis functions of fixed orbital angular momentum (OAM), a set of fixed helicity, or a basis consisting of a longitudinal (L) and two transverse (E and B) TAM waves. The symmetric traceless rank-2 tensor TAM waves can be similarly decomposed into a basis of fixed OAM or fixed helicity, or a basis that consists of a longitudinal (L), two vector (VE and VB, of opposite parity), and two tensor (TE and TB, of opposite parity) waves. We show how all of the vector and tensor TAM waves can be obtained by applying derivative operators to scalar TAM waves. This operator approach then allows one to decompose a vector field into three covariant scalar fields for the L, E, and B components and symmetric-traceless-tensor fields into five covariant scalar fields for the L, VE, VB, TE, and TB components. We provide projections of the vector and tensor TAM waves onto vector and tensor spherical harmonics. We provide calculational detail to facilitate the assimilation of this formalism into cosmological calculations. As an example, we calculate the power spectra of the deflection angle for gravitational lensing by density perturbations and by gravitational waves. We comment on an alternative approach to CMB fluctuations based on TAM waves. Our work may have applications elsewhere in field theory and in general relativity.

#### Sep 21, 2012

1209.0761 (/preprints)
2012-09-21, 10:53 

## [1209.0773] Perturbations of slowly rotating black holes: massive vector fields in the Kerr metric

Authors: Paolo Pani, Vitor Cardoso, Leonardo Gualtieri, Emanuele Berti, Akihiro Ishibashi

Date: 4 Sep 2012

Abstract: We discuss a general method to study linear perturbations of slowly rotating black holes which is valid for any perturbation field, and particularly advantageous when the field equations are not separable. As an illustration of the method we investigate massive vector (Proca) perturbations in the Kerr metric, which do not appear to be separable in the standard Teukolsky formalism. Working in a perturbative scheme, we discuss two important effects induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes and bound states with different azimuthal number m, and the coupling between axial and polar modes with different multipolar index l. We explicitly compute the perturbation equations up to second order in rotation, but in principle the method can be extended to any order. Working at first order in rotation we show that polar and axial Proca modes can be computed by solving two decoupled sets of equations, and we derive a single master equation describing axial perturbations of spin s=0 and s=+-1. By extending the calculation to second order we can study the superradiant regime of Proca perturbations in a self-consistent way. For the first time we show that Proca fields around Kerr black holes exhibit a superradiant instability, which is significantly stronger than for massive scalar fields. Because of this instability, astrophysical observations of spinning black holes provide the tightest upper limit on the mass of the photon: mv<4x10ˆ{-20} eV under our most conservative assumptions. Spin measurements for the largest black holes could reduce this bound to mv<10ˆ{-22} eV or lower.

#### Sep 21, 2012

1209.0773 (/preprints)
2012-09-21, 10:52 

## [1209.0964] Gravitational self-force and the effective-one-body formalism between the innermost stable circular orbit and the light ring

Authors: Sarp Akcay, Leor Barack, Thibault Damour, Norichika Sago

Date: 5 Sep 2012

Abstract: We compute the conservative piece of the gravitational self-force (GSF) acting on a particle of mass $m_1$ as it moves along an (unstable) circular geodesic orbit between the innermost stable circular orbit (ISCO) and the light ring of a Schwarzschild black hole of mass $m_2\gg m_1$. More precisely, we construct the function $h_{uu}(x) \equiv h_{\mu\nu} uˆ{\mu} uˆ{\nu}$ (related to Detweiler's gauge-invariant "redshift" variable), where $h_{\mu\nu}$ is the regularized metric perturbation in the Lorenz gauge, $uˆ{\mu}$ is the four-velocity of $m_1$, and $x\equiv [Gcˆ{-3}(m_1+m_2)\Omega]ˆ{2/3}$ is an invariant coordinate constructed from the orbital frequency $\Omega$. In particular, we explore the behavior of $h_{uu}$ just outside the "light ring" at $x=1/3$, where the circular orbit becomes null. Using the recently discovered link between $h_{uu}$ and the piece $a(u)$, linear in the symmetric mass ratio $nu$, of the main radial potential $A(u,\nu)$ of the Effective One Body (EOB) formalism, we compute $a(u)$ over the entire domain $0<u<1/3$ (extending previous results for $u\leq 1/5$). We find that $a(u)$ {\it diverges} like $\approx 0.25 (1-3u)ˆ{-½}$ at the light-ring limit, explain the physical origin of this divergent behavior, and discuss its consequences for the EOB formalism. We construct accurate global analytic fits for $a(u)$, valid on the entire domain $0<u<1/3$ (and possibly beyond), and give accurate numerical estimates of the values of $a(u)$ and its first 3 derivatives at the ISCO. In previous work we used GSF data on slightly eccentric orbits to compute a certain linear combination of $a(u)$ and its first two derivatives, involving also the $O(\nu)$ piece $\bar d(u)$ of a second EOB radial potential ${\bar D}(u,\nu)$. Combining these results with our present global analytic representation of $a(u)$, we numerically compute $\bar d(u)$ on the interval $0<u\leq 1/6$.

#### Sep 21, 2012

1209.0964 (/preprints)
2012-09-21, 10:52 

## [1209.0783] General Relativistic Simulations of Accretion Induced Collapse of Neutron Stars to Black Holes

Authors: Bruno Giacomazzo, Rosalba Perna

Date: 4 Sep 2012

Abstract: Neutron stars (NSs) in the astrophysical Universe are often surrounded by accretion disks. Accretion of matter onto a NS may increase its mass above the maximum value allowed by its equation of state, inducing its collapse to a black hole (BH). Here we study this process for the first time, in 3D, and in full general relativity. By considering three initial NS configurations, each with and without a surrounding disk (of mass ~7% M_{NS}), we investigate the effect of the accretion disk on the dynamics of the collapse and its imprint on both the gravitational wave (GW) and electromagnetic (EM) signals that can be emitted by these sources. We show in particular that, even if the GW signal is similar for the accretion induced collapse (AIC) and the collapse of a NS in vacuum (and detectable only for Galactic sources), the EM counterpart could allow to discriminate between these two types of events. In fact, our simulations show that, while the collapse of a NS in vacuum leaves no appreciable baryonic matter outside the event horizon, an AIC is followed by a phase of rapid accretion of the surviving disk onto the newly formed BH. The post-collapse accretion rates, on the order of ~10ˆ{-2} M_{sun} sˆ{-1}, make these events tantalizing candidates as engines of short Gamma-Ray Bursts.

#### Sep 21, 2012

1209.0783 (/preprints)
2012-09-21, 10:52 

## [1209.4524] The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole

Authors: E. Bon, P. Jovanovi&#x107;, P. Marziani, A. I. Shapovalova, N. Bon, V. Borka Jovanovi&#x107;, D. Borka, J. Sulentic, L. &#x10c;. Popovi&#x107;

Date: 20 Sep 2012

Abstract: One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole system in their cores. Here we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC 4151. Using a method similar to those typically applied for spectroscopic binary stars we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for an eccentric, sub-parsec Keplerian orbit of a 15.9-year period. The flux maximum in the lightcurve correspond to the approaching phase of a secondary component towards the observer. According to the obtained results we speculate that the periodic variations in the observed H{\alpha} line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into black hole mass growth process.

#### Sep 21, 2012

1209.4524 (/preprints)
2012-09-21, 10:30 

## [1209.4503] New tests of local Lorentz invariance of gravity with small-eccentricity binary pulsars

Authors: Lijing Shao, Norbert Wex

Date: 20 Sep 2012

Abstract: In the post-Newtonian parametrization of semi-conservative gravity theories, local Lorentz invariance (LLI) violation is characterized by two parameters, alpha_1 and alpha_2. In binary pulsars the isotropic violation of LLI in the gravitational sector leads to characteristic preferred frame effects (PFEs) in the orbital dynamics, if the barycenter of the binary is moving relative to the preferred frame with a velocity w. For small-eccentricity binaries, the effects induced by alpha_1 and alpha_2 decouple, and can therefore be tested independently. We use recent timing results of two compact pulsar-white dwarf binaries with known 3D velocity, PSRs J1012+5307 and J1738+0333, to constrain PFEs for strongly self-gravitating bodies. We derive a limit |alpha_2| < 1.8e-4 (95% CL), which is the most constraining limit for strongly self-gravitating systems up to now. Concerning alpha_1, we propose a new, robust method to constrain this parameter. Our most conservative result, alpha_1 = -0.4ˆ{+3.7}_{-3.1} e-5 (95% CL) from PSR J1738+0333, constitutes a significant improvement compared to current most stringent limits obtained both in Solar system and binary pulsar tests. We also derive corresponding limits for alpha_1 and alpha_2 for a preferred frame that is at rest with respect to our Galaxy, and preferred frames that locally co-move with the rotation of our Galaxy. (Abridged)

#### Sep 21, 2012

1209.4503 (/preprints)
2012-09-21, 10:29 

## [1209.4494] Gravitational waves from BH-NS binaries: Effective Fisher matrices and parameter estimation using higher harmonics

Authors: Hee-Suk Cho, Evan Ochsner, Richard O&#x27;Shaughnessy, Chunglee Kim, Chang-Hwan Lee

Date: 20 Sep 2012

Abstract: Inspiralling black hole-neutron star (BH-NS) binaries emit a complicated gravitational wave signature, produced by multiple harmonics sourced by their strong local gravitational field and further modulated by the orbital plane's precession. Some features of this complex signal are easily accessible to ground-based interferometers (e.g., the rate of change of frequency); others less so (e.g., the polarization content); and others unavailable (e.g., features of the signal out of band). For this reason, an ambiguity function (a diagnostic of dissimilarity) between two such signals varies on many parameter scales and ranges. In this paper, we present a method for computing an approximate, effective Fisher matrix from variations in the ambiguity function on physically pertinent scales which depend on the relevant signal to noise ratio. As a concrete example, we explore how higher harmonics improve parameter measurement accuracy. As previous studies suggest, for our fiducial BH-NS binaries and for plausible signal amplitudes, we see that higher harmonics at best marginally improve our ability to measure parameters. For non-precessing binaries, these Fisher matrices separate into intrinsic (mass, spin) and extrinsic (geometrical) parameters; higher harmonics principally improve our knowledge about the line of sight. For the precessing binaries, the extra information provided by higher harmonics is distributed across several parameters. We provide concrete estimates for measurement accuracy, using coordinates adapted to the precession cone in the detector's sensitive band.

#### Sep 21, 2012

1209.4494 (/preprints)
2012-09-21, 10:29 

## [1209.4097] Pulsations in Short GRBs from Black Hole-Neutron Star Mergers

Authors: Nicholas Stone, Abraham Loeb, Edo Berger

Date: 18 Sep 2012

Abstract: The precise origin of short gamma ray bursts (SGRBs) remains an important open question in relativistic astrophysics. Increasingly, observational evidence suggests the merger of a binary compact object system as the source for most SGRBs, but it is currently unclear how to distinguish observationally between a binary neutron star progenitor and a black hole-neutron star progenitor. We suggest the quasi-periodic signal of jet precession as an observational signature of SGRBs originating in mixed binary systems, and quantify both the fraction of mixed binaries capable of producing SGRBs, and the distributions of precession amplitudes and periods. The difficulty inherent in disrupting a neutron star outside the horizon of a stellar-mass black hole biases the jet precession signal towards low amplitude and high frequency. Precession periods of ~ 0.01-0.1 s and disk-BH spin misalignments ~10 degrees are generally expected, although sufficiently high viscosity may prevent the accumulation of multiple precession periods during the SGRB. The precessing jet will naturally cover a larger solid angle in the sky than would standard SGRB jets, enhancing observability for both prompt emission and optical afterglows.

#### Sep 20, 2012

1209.4097 (/preprints)
2012-09-20, 09:28 

## [1208.3906] Resonantly enhanced and diminished strong-field gravitational-wave fluxes

Authors: Eanna E. Flanagan, Scott A. Hughes, Uchupol Ruangsri

Date: 20 Aug 2012

Abstract: The inspiral of a stellar mass ($1 - 100\,M_\odot$) compact body into a massive ($10ˆ5 - 10ˆ7\,M_\odot$) black hole has been a focus of much effort, both for the promise of such systems as astrophysical sources of gravitational waves, and because they are a clean limit of the general relativistic two-body problem. Our understanding of this problem has advanced significantly in recent years, with much progress in modeling the "self force" arising from the small body's interaction with its own spacetime deformation. Recent work has shown that this self interaction is especially interesting when the frequencies associated with the orbit's $\theta$ and $r$ motions are in an integer ratio: $\Omega_\theta/\Omega_r = \beta_\theta/\beta_r$, with $\beta_\theta$ and $\beta_r$ both integers. In this paper, we show that key aspects of the self interaction for such "resonant" orbits can be understood with a relatively simple Teukolsky-equation-based calculation of gravitational-wave fluxes. We show that fluxes from resonant orbits depend on the relative phase of radial and angular motions. The purpose of this paper is to illustrate in simple terms how this phase dependence arises using tools that are good for strong-field orbits, and to present a first study of how strongly the fluxes vary as a function of this phase and other orbital parameters. Future work will use the full dissipative self force to examine resonant and near resonant strong-field effects in greater depth.

#### Sep 19, 2012

1208.3906 (/preprints)
2012-09-19, 18:07 

## [1209.4085] Eccentric black hole mergers and zoom-whirl behavior from elliptic inspirals to hyperbolic encounters

Authors: Roman Gold, Bernd Bruegmann

Date: 18 Sep 2012

Abstract: We perform a parameter study of non-spinning, equal and unequal mass black hole binaries on generic, eccentric orbits in numerical relativity. The linear momentum considered ranges from that of a circular orbit to ten times that value. We discuss the different manifestations of zoom-whirl behavior in the hyperbolic and the elliptic regime. The hyperbolic data set applies to dynamical capture scenarios (e.g. in globular clusters). Evolutions in the elliptic regime correspond to possible end states of supermassive black hole binaries. We spot zoom-whirl behavior for eccentricities as low as $e\sim0.5$, i.e. within the expected range of eccentricities in massive black hole binaries from galaxy mergers and binaries near galactic centers. The resulting gravitational waveforms reveal a rich structure, which will effectively break degeneracies in parameter space improving parameter estimation.

#### Sep 19, 2012

1209.4085 (/preprints)
2012-09-19, 18:07 

## [1208.3931] Capture of non-relativistic particles in eccentric orbits by a Kerr black hole

Authors: Clifford M. Will

Date: 20 Aug 2012

Abstract: We obtain approximate analytic expressions for the critical value of the total angular momentum of a non-relativistic test particle moving in the Kerr geometry, such that it will be captured by the black hole. The expressions apply to arbitrary orbital inclinations, and are accurate over the entire range of angular momentum for the Kerr black hole. The expressions can be easily implemented in N-body simulations of the evolution of star clusters around massive galactic black holes, where such captures play an important role.

#### Sep 19, 2012

1208.3931 (/preprints)
2012-09-19, 18:06 

## [1208.3703] Quantum Geometry and Interferometry

Authors: Craig Hogan

Date: 17 Aug 2012

Abstract: All existing experimental results are currently interpreted using classical geometry. However, there are theoretical reasons to suspect that at a deeper level, geometry emerges as an approximate macroscopic behavior of a quantum system at the Planck scale. If directions in emergent quantum geometry do not commute, new quantum-geometrical degrees of freedom can produce detectable macroscopic deviations from classicality: spatially coherent, transverse position indeterminacy between any pair of world lines, with a displacement amplitude much larger than the Planck length. Positions of separate bodies are entangled with each other, and undergo quantum-geometrical fluctuations that are not describable as metric fluctuations or gravitational waves. These fluctuations can either be cleanly identified or ruled out using interferometers. A Planck-precision test of the classical coherence of space-time on a laboratory scale is now underway at Fermilab.

#### Sep 19, 2012

1208.3703 (/preprints)
2012-09-19, 18:06 

## [1208.4365] Halo millisecond pulsars ejected by intermediate mass black holes in globular clusters

Authors: Alberto Sesana, Nicola Sartore, Bernadetta Devecchi, Andrea Possenti

Date: 21 Aug 2012

Abstract: Intermediate mass black holes (IMBHs) are among the most elusive objects in contemporary astrophysics. Both theoretical and observational evidence of their existence is subject of debate. Conversely, both theory and observations confirm the presence of a large population of millisecond pulsars (MSPs) with low mass companions residing in globular cluster (GC) centers. If IMBHs are common in GC centers as well, then dynamical interactions will inevitably break up many of these binaries, causing the ejection of several fast MSPs in the Galactic halo. Such population of fast halo MSPs, hard to produce with 'standard' MSP generation mechanisms, would provide a strong, albeit indirect, evidence of the presence of a substantial population of IMBHs in GCs. In this paper we study in detail the dynamical formation and evolution of such fast MSPs population, highlighting the relevant observational properties and assessing detection prospects with forthcoming radio surveys.

#### Sep 19, 2012

1208.4365 (/preprints)
2012-09-19, 18:05 

## [1208.4596] Model-independent test of gravity with a network of ground-based gravitational-wave detectors

Authors: Kazuhiro Hayama, Atsushi Nishizawa

Date: 22 Aug 2012

Abstract: The observation of gravitational waves with a global network of interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will make it possible to probe into the nature of space-time structure. Besides Einstein's general theory of relativity, there are several theories of gravitation that passed experimental tests so far. The gravitational-wave observation provides a new experimental test of alternative theories of gravity because a gravitational wave may have at most six independent modes of polarization, of which properties and number of modes are dependent on theories of gravity. This paper proposes a method to reconstruct the independent modes of polarization in time-series data of an advanced detector network. Since the method does not rely on any specific model, it gives model-independent test of alternative theories of gravity.

#### Sep 19, 2012

1208.4596 (/preprints)
2012-09-19, 18:04 

## [1209.3724] Local measurement of \Lambda{} using pulsar timing arrays

Authors: Dom&#xe8;nec Espriu, Daniel Puigdom&#xe8;nech

Date: 17 Sep 2012

Abstract: We have considered the propagation of gravitational waves (GW) in de Sitter space time and how a non-zero value of the cosmological constant might affect their detection in pulsar timing arrays (PTA). If \Lambda{} is different from zero waves are non-linear in Friedmann-Robertson-Walker coordinates and although the amount of non-linearity is very small it gives noticeable effects for GW originating in extragalactic sources such as spiraling black hole binaries. The results indicate that the timing residuals induced by gravitational waves from such sources in PTA would show a peculiar angular dependence with a marked enhancement around a particular value of the angle subtended by the source and the pulsars, depending mainly on the actual value of the cosmological constant and the distance to the source. The position of the peak could represent a gauge of the value of \Lambda. The enhancement that the new effect brings about could facilitate the first direct detection of gravitational waves while representing a local measurement of \Lambda.

#### Sep 19, 2012

1209.3724 (/preprints)
2012-09-19, 18:03 

## [1209.3712] Precession during merger 1: Strong polarization changes are observationally accessible features of strong-field gravity during binary black hole merger

Authors: R. O&#x27;Shaughnessy (1), L. London (2), J. Healy (2), D. Shoemaker (2) ((1) University of Wisconsin-Milwaukee, (2) Center for Relativistic Astrophysics, Georgia Tech)

Date: 17 Sep 2012

Abstract: The short gravitational wave signal from the merger of compact binaries encodes a surprising amount of information about the strong-field dynamics of merger into frequencies accessible to ground-based interferometers. In this paper we describe a previously-unknown "precession" of the peak emission direction with time, both before and after the merger, about the total angular momentum direction. We demonstrate the gravitational wave polarization encodes the orientation of this direction to the line of sight. We argue the effects of polarization can be estimated nonparametrically, directly from the gravitational wave signal as seen along one line of sight, as a slowly-varying feature on top of a rapidly-varying carrier. After merger, our results can be interpreted as a coherent excitation of quasinormal modes of different angular orders, a superposition which naturally "precesses" and modulates the line-of-sight amplitude. Recent analytic calculations have arrived at a similar geometric interpretation. We suspect the line-of-sight polarization content will be a convenient observable with which to define new high-precision tests of general relativity using gravitational waves. Additionally, as the nonlinear merger process seeds the initial coherent perturbation, we speculate the amplitude of this effect provides a new probe of the strong-field dynamics during merger. To demonstrate the ubiquity of the effects we describe, we summarize the post-merger evolution of 104 generic precessing binary mergers. Finally, we provide estimates for the detectable impacts of precession on the waveforms from high-mass sources. These expressions may identify new precessing binary parameters whose waveforms are dissimilar from the existing sample.

#### Sep 19, 2012

1209.3712 (/preprints)
2012-09-19, 18:02 

## [1209.3511] The effective field theory treatment of quantum gravity

Authors: John F. Donoghue

Date: 16 Sep 2012

Abstract: This is a pedagogical introduction to the treatment of quantum general relativity as an effective field theory. It starts with an overview of the methods of effective field theory and includes an explicit example. Quantum general relativity matches this framework and I discuss gravitational examples as well as the limits of the effective field theory. I also discuss the insights from effective field theory on the gravitational effects on running couplings in the perturbative regime.

#### Sep 19, 2012

1209.3511 (/preprints)
2012-09-19, 18:02 

## [1209.3986] Power spectrum of gravitational waves from unbound compact binaries

Authors: Lorenzo De Vittori, Philippe Jetzer, Antoine Klein

Date: 18 Sep 2012

Abstract: Unbound interacting compact binaries emit gravitational radiation in a wide frequency range. Since short burst-like signals are expected in future detectors, such as LISA or advanced LIGO, it is interesting to study their energy spectrum and the position of the frequency peak. Here we derive them for a system of massive objects interacting on hyperbolic orbits within the quadrupole approximation, following the work of Capozziello et al. In particular, we focus on the derivation of an analytic formula for the energy spectrum of the emitted waves. Within numerical approximation our formula is in agreement with the two known limiting cases: for the eccentricity {\epsilon} = 1, the parabolic case, whose spectrum was computed by Berry and Gair, and the large {\epsilon} limit with the formula given by Turner.

#### Sep 19, 2012

1209.3986 (/preprints)
2012-09-19, 18:01 

## [1209.4024] Cosmological Backgrounds of Gravitational Waves and eLISA

Authors: Jean-Francois Dufaux

Date: 18 Sep 2012

Abstract: We review cosmological backgrounds of gravitational waves with a particular attention to the scientific potential of the eLISA/NGO mission. After an overview of cosmological backgrounds and detectors, we consider different cosmological sources that could lead to an observable signal. We then study the backgrounds produced by first-order phase transitions and networks of cosmic strings, assessing the prospects for their detection.

#### Sep 19, 2012

1209.4024 (/preprints)
2012-09-19, 18:01 

## [1208.5279] Dynamical Capture Binary Neutron Star Mergers

Authors: William E. East, Frans Pretorius

Date: 27 Aug 2012

Abstract: We study dynamical capture, binary neutron star mergers as may arise in dense stellar regions such as globular clusters. Using general-relativistic hydrodynamics we find that these mergers can result in the prompt collapse to a black hole or in the formation of a hypermassive neutron star, depending not only on the neutron star equation of state, but also on impact parameter. We also find that these mergers can produce accretion disks of up to a tenth of a solar mass, and unbound ejected material of up to a few percent of a solar mass. We comment on the gravitational radiation and electromagnetic transients that these sources may produce.

#### Sep 17, 2012

1208.5279 (/preprints)
2012-09-17, 13:45 

## [1208.5051] Rapid Orbital Decay in the 12.75-minute WD WD Binary J0651 2844

Authors: J. J. Hermes, Mukremin Kilic, Warren R. Brown, D. E. Winget, Carlos Allende Prieto, A. Gianninas, Anjum S. Mukadam, Antonio Cabrera-Lavers, Scott J. Kenyon

Date: 24 Aug 2012

Abstract: We report the detection of orbital decay in the 12.75-min, detached binary white dwarf (WD) SDSS J065133.338+284423.37 (hereafter J0651). Our photometric observations over a 13-month baseline constrain the orbital period to 765.206543(55) s and indicate the orbit is decreasing as a rate of (-9.8 +/- 2.8) x 10ˆ(-12) s/s (or -0.31 +/- 0.09 ms/yr). We revise the system parameters based on our new photometric and spectroscopic observations: J0651 contains two WDs with M1 = 0.26 +/- 0.04 Msun and M2 = 0.50 +/- 0.04 Msun. General relativity predicts orbital decay due to gravitational wave radiation of (-8.2 +/- 1.7) x 10ˆ(-12) s/s (or -0.26 +/- 0.05 ms/yr). Our observed rate of orbital decay is consistent with this expectation. J0651 is currently the second-loudest gravitational wave source known in the milli-Hertz range and the loudest non-interacting binary, which makes it an excellent verification source for future missions aimed at directly detecting gravitational waves. Our work establishes the feasibility of monitoring this system's orbital period decay at optical wavelengths.

#### Sep 17, 2012

1208.5051 (/preprints)
2012-09-17, 13:45 

## [1208.5251] The typical mass ratio and typical final spin in supermassive black hole mergers

Authors: L&#xe1;szl&#xf3; &#xc1;. Gergely, Peter L. Biermann

Date: 26 Aug 2012

Abstract: We prove that merging supermassive black holes (SMBHs) typically have neither equal masses, nor is their mass ratio too extreme. The majority of such mergers fall into the mass ratio range of 1:30 to 1:3, implying a spin flip during the inspiral. We also present a simple expression for the final spin $\chi_{f}$ of the emerging SMBH, as function of the mass ratio, initial spin magnitudes, and orientation of the spins with respect to the orbital plane and each other. This formula approximates well more cumbersome expressions obtained from the fit with numerical simulations. By integrating over all equally likely orientations for precessing mergers we determine a lower approximant to the final spin distribution as function of the mass ratio alone. By folding this with the derived mass ratio dependent merger rate we derive a lower bound to the typical final spin value after mergers. We repeat the procedure deriving an upper bound for the typical spin in the case when the spins are aligned to the orbital angular momentum, such that there is no precession in the system. Both slopes of $\chi_{f}$ as function of the initial spins being smaller than one lead to two attractors at $\chi_{f}ˆ{prec}=0.2$ and \chi_{f}ˆ{align}=0.45, respectively. Real mergers, biased toward partial alignment by interactions with the environment (accretion, host galaxy, etc.) would generate a typical final spin lying between these two limiting values. These are the typical values of the spin after the merger, starting from which the spin can built up by further gaseous accretion.

#### Sep 17, 2012

1208.5251 (/preprints)
2012-09-17, 13:45 

## [1208.5227] Maximum elastic deformations of relativistic stars

Authors: Nathan K. Johnson-McDaniel, Benjamin J. Owen

Date: 26 Aug 2012

#### Sep 17, 2012

1208.5227 (/preprints)
2012-09-17, 13:45 

## [1208.5237] The tetralogy of Birkhoff theorems

Authors: Hans-J&#xfc;rgen Schmidt

Date: 26 Aug 2012

Abstract: We classify the existent Birkhoff-type theorems into four classes: First, in field theory, the theorem states the absence of helicity 0- and spin 0-parts of the gravitational field. Second, in relativistic astrophysics, it is the statement that the gravitational far-field of a spherically symmetric star carries, apart from its mass, no information about the star; therefore, a radially oscillating star has a static gravitational far-field. Third, in mathematical physics, Birkhoff's theorem reads: up to singular exceptions of measure zero, the spherically symmetric solutions of Einstein's vacuum field equation with Lambda = 0 can be expressed by the Schwarzschild metric; for Lambda unequal 0, it is the Schwarzschild-de Sitter metric instead. Fourth, in differential geometry, any statement of the type: every member of a family of pseudo-Riemannian space-times has more isometries than expected from the original metric ansatz, carries the name Birkhoff-type theorem. Within the fourth of these classes we present some new results with further values of dimension and signature of the related spaces; including them are some counterexamples: families of space-times where no Birkhoff-type theorem is valid. These counterexamples further confirm the conjecture, that the Birkhoff-type theorems have their origin in the property, that the two eigenvalues of the Ricci tensor of two-dimensional pseudo-Riemannian spaces always coincide, a property not having an analogy in higher dimensions. Hence, Birkhoff-type theorems exist only for those physical situations which are reducible to two dimensions.

#### Sep 17, 2012

1208.5237 (/preprints)
2012-09-17, 13:44 

## [1208.5102] Gravitational Waves from Quasi-Circular Black Hole Binaries in Dynamical Chern-Simons Gravity

Authors: Kent Yagi, Nicolas Yunes, Takahiro Tanaka

Date: 25 Aug 2012

Abstract: Dynamical Chern-Simons gravity cannot be strongly constrained with current experiments because it reduces to General Relativity in the weak-field limit. This theory, however, introduces modifications in the non-linear, dynamical regime, and thus, it could be greatly constrained with gravitational waves from the late inspiral of black hole binaries. We complete the first self-consistent calculation of such gravitational waves in this theory. We find that future gravitational wave detectors could place constraints that are 6 orders of magnitude stronger than current ones.

#### Sep 17, 2012

1208.5102 (/preprints)
2012-09-17, 13:44 

## [1208.5975] Gravitational wave signal from massive gravity

Authors: A. Emir Gumrukcuoglu, Sachiko Kuroyanagi, Chunshan Lin, Shinji Mukohyama, Norihiro Tanahashi

Date: 29 Aug 2012

Abstract: We discuss the detectability of gravitational waves with a time dependent mass contribution, by means of the stochastic gravitational wave observations. Such a mass term typically arises in the cosmological solutions of massive gravity theories. We conduct the analysis based on a general quadratic action, and thus the results apply universally to any massive gravity theories in which modification of general relativity appears primarily in the tensor modes. The primary manifestation of the modification in the gravitational wave spectrum is a sharp peak. The position and height of the peak carry information on the present value of the mass term, as well as the duration of the inflationary stage. We also discuss the detectability of such a gravitational wave signal using the future-planned gravitational wave observatories.

#### Sep 17, 2012

1208.5975 (/preprints)
2012-09-17, 13:43 

## [1208.5839] Intermediate behavior of Kerr tails

Authors: An&#x131;l Zengino&#x11f;lu, Gaurav Khanna, Lior M. Burko

Date: 29 Aug 2012

Abstract: The numerical investigation of wave propagation in the asymptotic domain of Kerr spacetime has only recently been possible thanks to the construction of suitable hyperboloidal coordinates. The asymptotics revealed a puzzle in the decay rates of scalar fields: the late-time rates seemed to depend on whether finite distance observers are in the strong field domain or far away from the rotating black hole. In this paper we study late-time decay rates using a horizon-penetrating, hyperboloidal slicing with transmitting layers attached to a compact domain in Boyer--Lindquist coordinates. The technical construction of transmitting layers for Kerr spacetime should be useful in future studies of wave propagation. We discuss splitting of local decay rates in certain projected modes and in the full field. The splitting in the full field rates is explained by competition between projected modes. For the splitting in certain projected modes we argue that, asymptotically in time, the strong field rates are valid at all finite distances, but at any given late time, there are three domains with different local decay rates whose boundaries move during evolution.

#### Sep 17, 2012

1208.5839 (/preprints)
2012-09-17, 13:42 

## [1208.5869] The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries

Authors: Francesco Pannarale

Date: 29 Aug 2012

Abstract: We present a model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with parallel orbital angular momentum and initial black hole spin. This approach is based on the Buonanno, Kidder, and Lehner method for binary black holes and it is successfully tested against the results of numerical-relativity simulations: the dimensionless spin parameter is predicted with absolute error $\lesssim 0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its distribution being pronouncedly peaked at 1%. Our approach and the fit to the torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use analytical model that accurately describes the remnant of BH-NS mergers. We investigate the space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state. We provide indirect support to the cosmic censorship conjecture for black hole remnants of black hole-neutron star mergers. We show that the presence of a neutron star affects the quasi-normal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish binary black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state.

#### Sep 17, 2012

1208.5869 (/preprints)
2012-09-17, 13:42 

## [1208.6489] Asymptotically Matched Spacetime Metric for Non-Precessing, Spinning Black Hole Binaries

Authors: Louis Gallouin, Hiroyuki Nakano, Nicolas Yunes, Manuela Campanelli

Date: 31 Aug 2012

Abstract: We construct a closed-form, fully analytical 4-metric that approximately represents the spacetime evolution of non-precessing, spinning black hole binaries from infinite separations up to a few orbits prior to merger. We employ the technique of asymptotic matching to join a perturbed Kerr metric in the neighborhood of each spinning black hole to a near-zone, post-Newtonian metric farther out. The latter is already naturally matched to a far-zone, post-Minkowskian metric that accounts for full temporal retardation. The result is a 4-metric that is approximately valid everywhere in space and in a small bundle of spatial hypersurfaces. We here restrict our attention to quasi- circular orbits, but the method is valid for any orbital motion or physical scenario, provided an overlapping region of validity or buffer zone exists. A simple extension of such a metric will allow for future studies of the accretion disk and jet dynamics around spinning back hole binaries.

#### Sep 17, 2012

1208.6489 (/preprints)
2012-09-17, 13:41 

## [1208.6274] Spin Evolution of Supermassive Black Holes and Galactic Nuclei

Authors: David Merritt, Eugene Vasiliev

Date: 30 Aug 2012

Abstract: The spin angular momentum S of a supermassive black hole (SBH) precesses due to torques from orbiting stars, and the stellar orbits precess due to dragging of inertial frames by the spinning hole. We solve the coupled post-Newtonian equations describing the joint evolution of S and the stellar angular momenta Lj, j = 1…N in spherical, rotating nuclear star clusters. In the absence of gravitational interactions between the stars, two evolutionary modes are found: (1) nearly uniform precession of S about the total angular momentum vector of the system; (2) damped precession, leading, in less than one precessional period, to alignment of S with the angular momentum of the rotating cluster. Beyond a certain distance from the SBH, the time scale for angular momentum changes due to gravitational encounters between the stars is shorter than spin-orbit precession times. We present a model, based on the Ornstein-Uhlenbeck equation, for the stochastic evolution of star clusters due to gravitational encounters and use it to evaluate the evolution of S in nuclei where changes in the Lj are due to frame dragging close to the SBH and to encounters farther out. Long-term evolution in this case is well described as uniform precession of the SBH about the cluster's rotational axis, with an increasingly important stochastic contribution when SBH masses are small. Spin precessional periods are predicted to be strongly dependent on nuclear properties, but typical values are 10-100 Myr for low-mass SBHs in dense nuclei, 100 Myr - 10 Gyr for intermediate mass SBHs, and > 10 Gyr for the most massive SBHs. We compare the evolution of SBH spins in stellar nuclei to the case of torquing by an inclined, gaseous accretion disk.

#### Sep 17, 2012

1208.6274 (/preprints)
2012-09-17, 13:40 

## [1209.0718] A method to estimate the significance of coincident gravitational-wave observations from compact binary coalescence

Authors: Kipp Cannon, Chad Hanna, Drew Keppel

Date: 4 Sep 2012

Abstract: Coalescing compact binary systems consisting of neutron stars and/or black holes should be detectable with upcoming advanced gravitational-wave detectors such as LIGO, Virgo, GEO and {KAGRA}. Gravitational-wave experiments to date have been riddled with non-Gaussian, non-stationary noise that makes it challenging to ascertain the significance of an event. A popular method to estimate significance is to time shift the events collected between detectors in order to establish a false coincidence rate. Here we propose a method for estimating the false alarm probability of events using variables commonly available to search candidates that does not rely on explicitly time shifting the events while still capturing the non-Gaussianity of the data. We present a method for establishing a statistical detection of events in the case where several silver-plated (3--5$\sigma$) events exist but not necessarily any gold-plated ($>5\sigma$) events. We use LIGO data and a simulated, realistic, blind signal population to test our method.

#### Sep 17, 2012

1209.0718 (/preprints)
2012-09-17, 13:39 

## [1209.0611] Hypot\ese th\'eorique concernant l'induction d'un champ gravitationnel de type vectoriel g\'en\'er\'e par le d\'eplacement acc\'el\'er\'e des masses en mouvement

Authors: Mathieu Beau (STP-DIAS)

Date: 4 Sep 2012

Abstract: We propose a vectorial field theory (G) based on a so-called \textit{gravitational induction principle} saying that a density current of accelerated particles generate a vectorial field $G_\mu$. The aim of this article is to give a first approach of this theory. We fist construct a Lagrangian $L_G=-mcˆ2 G_\mu(x)\ddot{x}ˆ\mu$ (where $m$ is the mass of the particle, $\ddot{x}ˆ\mu$ its acceleration) analogous to the electrodynamic Lagrangian $L_{ED}=-q A_\mu(x)\dot{x}ˆ\mu$ (where $q$ is the charge of the particle, $\dot{x}ˆ\mu$ its velocity) and then we give the analogous field equations based on the induction principle. Using these field equations, we establish new kind of gravitomagnetic equations (GEM-G) valid for small velocities, analogous to the gravitomagnetic field equation (GEM) proved by the general theory of the relativity (RG). Then, we will propose a first approach about the description of the vectorial field theory (G) in the framework of the general relativity theory (RG), we will give the field equations and we will discuss the conceptual consequences of a theory of gravitation with both different fields.

#### Sep 17, 2012

1209.0611 (/preprints)
2012-09-17, 13:39 

## [1209.0635] Planetary ephemerides and gravity tests in the solar system

Authors: A. Fienga

Date: 4 Sep 2012

Abstract: We review here the tests of fundamental physics based on the dynamics of solar system objects.

#### Sep 17, 2012

1209.0635 (/preprints)
2012-09-17, 13:39 

## [1209.0465] Black hole bombs and photon mass bounds

Authors: Paolo Pani, Vitor Cardoso, Leonardo Gualtieri, Emanuele Berti, Akihiro Ishibashi

Date: 3 Sep 2012

Abstract: Generic extensions of the standard model predict the existence of ultralight bosonic degrees of freedom. Several ongoing experiments are aimed at detecting these particles or constraining their mass range. Here we show that massive vector fields around rotating black holes can give rise to a strong superradiant instability which extracts angular momentum from the hole. The observation of supermassive spinning black holes imposes limits on this mechanism. We show that current supermassive black hole spin estimates provide the tightest upper limits on the mass of the photon (mv<4x10ˆ{-20} eV according to our most conservative estimate), and that spin measurements for the largest known supermassive black holes could further lower this bound to mv<10ˆ{-22} eV. Our analysis relies on a novel framework to study perturbations of rotating Kerr black holes in the slow-rotation regime, that we developed up to second order in rotation, and that can be extended to other spacetime metrics and other theories.

#### Sep 17, 2012

1209.0465 (/preprints)
2012-09-17, 13:38 

## [1209.0595] On the gravitational wave background from compact binary coalescence in the band of ground-based interferometers

Authors: Xing-Jiang Zhu, Eric J. Howell, David G. Blair, Zong-Hong Zhu

Date: 4 Sep 2012

Abstract: This paper reports a comprehensive study on the gravitational wave (GW) background from compact binary coalescences. We consider in our calculations newly available observation-based neutron star and black hole mass distributions and complete analytical waveforms that include post-Newtonian amplitude corrections. Our results show that: (i) post-Newtonian effects cause a small reduction in the GW background signal; (ii) below 100 Hz the background depends primarily on the local coalescence rate $r_0$ and the average chirp mass and is independent of the chirp mass distribution; (iii) the effects of cosmic star formation rates and delay times between the formation and merger of binaries are linear below 100 Hz and can be represented by a single parameter within a factor of ~ 2; (iv) a simple power law model of the energy density parameter $\Omega_{GW}(f) ~ fˆ{2/3}$ up to 50-100 Hz is sufficient to be used as a search template for ground-based interferometers. In terms of the detection prospects of the background signal, we show that: (i) detection (a signal-to-noise ratio of 3) within one year of observation by the Advanced LIGO detectors (H1-L1) requires a coalescence rate of $r_0 = 3 (0.2) Mpcˆ{-3} Myrˆ{-1}$ for binary neutron stars (binary black holes); (ii) this limit on $r_0$ could be reduced 3-fold for two co-located detectors, whereas the currently proposed worldwide network of advanced instruments gives only ~ 30% improvement in detectability; (iii) the improved sensitivity of the planned Einstein Telescope allows not only confident detection of the background but also the high frequency components of the spectrum to be measured. Finally we show that the residual noise arising from sub-threshold binary neutron star merger events will be a challenging issue for terrestrial searches of primordial GWs from the early Universe.

#### Sep 17, 2012

1209.0595 (/preprints)
2012-09-17, 13:38 

## [1209.2971] Continuous Gravitational Waves from Isolated Galactic Neutron Stars in the Advanced Detector Era

Authors: Leslie Wade, Xavier Siemens, David Kaplan, Benjamin Knispel, Bruce Allen

Date: 13 Sep 2012

Abstract: We consider a simulated population of isolated Galactic neutron stars. The rotational frequency of each neutron star evolves through a combination of electromagnetic and gravitational wave emission. The magnetic field strength dictates the dipolar emission, and the ellipticity (a measure of a neutron star's deformation) dictates the gravitational wave emission. Through both analytic and numerical means, we assess the detectability of the Galactic neutron star population and bound the magnetic field strength and ellipticity parameter space of Galactic neutron stars with or without a direct gravitational wave detection. While our simulated population is primitive, this work establishes a framework by which future efforts can be conducted.

#### Sep 17, 2012

1209.2971 (/preprints)
2012-09-17, 13:37 

## [1209.3027] Electromagnetic transients as triggers in searches for gravitational waves from compact binary mergers

Authors: Luke Zoltan Kelley, Ilya Mandel, Enrico Ramirez-Ruiz

Date: 13 Sep 2012

Abstract: The detection of an electromagnetic transient which may originate from a binary neutron star merger can increase the probability that a given segment of data from the LIGO-Virgo ground-based gravitational-wave detector network contains a signal from a binary coalescence. Additional information contained in the electromagnetic signal, such as the sky location or distance to the source, can help rule out false alarms, and thus lower the necessary threshold for a detection. Here, we develop a framework for determining how much sensitivity is added to a gravitational-wave search by triggering on an electromagnetic transient. We apply this framework to a variety of relevant electromagnetic transients, from short GRBs to signatures of r-process heating to optical and radio orphan afterglows. We compute the expected rates of multi-messenger observations in the Advanced detector era, and find that searches triggered on short GRBs — with current high-energy instruments, such as Fermi — and nucleosynthetic ‘kilonovae’ — with future optical surveys, like LSST — can boost the number of multi-messenger detections by 15% and 40%, respectively, for a binary neutron star progenitor model. Short GRB triggers offer precise merger timing, but suffer from detection rates decreased by beaming and the high a priori probability that the source is outside the LIGO-Virgo sensitive volume. Isotropic kilonovae, on the other hand, could be commonly observed within the LIGO-Virgo sensitive volume with an instrument roughly an order of magnitude more sensitive than current optical surveys. We propose that the most productive strategy for making multi-messenger gravitational-wave observations is using triggers from future deep, optical all-sky surveys, with characteristics comparable to LSST, which could make as many as ten such coincident observations a year.

#### Sep 17, 2012

1209.3027 (/preprints)
2012-09-17, 13:36 

## [1209.3024] Testing General Relativity in the Strong-Field Regime with Observations of Black Holes in the Electromagnetic Spectrum

Authors: Tim Johannsen (Waterloo, Perimeter, Arizona)

Date: 13 Sep 2012

Abstract: General relativity has been tested by many experiments, which, however, almost exclusively probe weak spacetime curvatures. In this thesis, I create two frameworks for testing general relativity in the strong-field regime with observations of black holes in the electromagnetic spectrum using current or near-future instruments. In the first part of this thesis, I design tests of the no-hair theorem, which uniquely characterizes the nature of black holes in general relativity in terms of their masses and spins and which states that these compact objects are described by the Kerr metric. I investigate a quasi-Kerr metric and construct a Kerr-like spacetime, both of which contain an independent parameter in addition to mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric has to be zero. I show that already moderate changes of the deviation parameters in either metric lead to significant modifications of the observed signals. I apply this framework to the imaging of supermassive black holes using very-long baseline interferometry as well as to the quasi-periodic variability and relativistically broadened iron lines observed in both galactic and supermassive black holes. In the second part of this thesis, I devise a method to test the predicted evaporation of black holes in Randall-Sundrum-type braneworld gravity through the orbital evolution of black-hole X-ray binaries and obtain constraints on the size of the extra dimension from A0620-00 and XTE J1118+480.

#### Sep 17, 2012

1209.3024 (/preprints)
2012-09-17, 13:35 

## [1209.0667] Gravitational Waves: Sources, Detectors and Searches

Authors: Keith Riles

Date: 4 Sep 2012

Abstract: Gravitational wave science should transform in this decade from a study of what has not been seen to a full-fledged field of astronomy in which detected signals reveal the nature of cataclysmic events and exotic objects. The LIGO Scientific Collaboration and Virgo Collaboration have recently completed joint data runs of unprecedented sensitivities to gravitational waves. So far, no gravitational radiation has been seen (although data mining continues). It seems likely that the first detection will come from 2nd-generation LIGO and Virgo interferometers now being installed. These new detectors are expected to detect ~40 coalescences of neutron star binary systems per year at full sensitivity. At the same time, research and development continues on 3rd-generation underground interferometers and on space-based interferometers. In parallel there is a vigorous effort in the radio pulsar community to detect ~several-nHz gravitational waves via the timing residuals from an array of pulsars at different locations in the sky. As the dawn of gravitational wave astronomy nears, this review, intended primarily for interested particle and nuclear physicists, describes what we have learned to date and the prospects for direct discovery of gravitational waves.

#### Sep 15, 2012

1209.0667 (/preprints)
2012-09-15, 23:32 

## [1209.2658] Cyg X-3: a Galactic double black hole or black hole-neutron star progenitor

Authors: Krzysztof Belczynski, Tomasz Bulik, Ilya Mandel, B.S. Sathyaprakash, Andrzej Zdziarski, Joanna Mikolajewska

Date: 12 Sep 2012

Abstract: There are no known double black hole (BH-BH) or black hole-neutron star (BH-NS) systems. We argue that Cyg X-3 is a very likely BH-BH or BH-NS progenitor. This Galactic X-ray binary consists of a compact object, wind-fed by a Wolf-Rayet (WR) type companion. Based on a comprehensive analysis of observational data, it was recently argued that Cyg X-3 harbors a 2-4.5 Msun BH and a 7.5-14.2 Msun WR companion. We find that the fate of such a binary leads to the prompt (<1 Myr) formation of a close BH-BH system for the high end of the allowed WR mass (M_WR>13 Msun). For the low- to mid-mass range of the WR star (M_WR=7-10 Msun) Cyg X-3 is most likely (probability 70%) disrupted when WR ends up as a supernova. However, with smaller probability, it may form a wide (15%) or a close (15%) BH-NS system. The advanced LIGO/VIRGO detection rate for mergers of BH-BH systems from the Cyg X-3 formation channel is 10 per year, while it drops down to 0.1 per year for BH-NS systems. If Cyg X-3 in fact hosts a low mass BH and massive WR star, it lends additional support for the existence of BH-BH/BH-NS systems.

#### Sep 12, 2012

1209.2658 (/preprints)
2012-09-12, 19:28 

## [1209.2534] Constraining Gravity with LISA Detections of Binaries

Authors: Priscilla Canizares (1), Jonathan R. Gair (1), Carlos F. Sopuerta (2) ((1) IoA, Cambridge, (2) ICE, CSIC-IEEC)

Date: 12 Sep 2012

Abstract: General Relativity (GR) describes gravitation well at the energy scales which we have so far been able to achieve or detect. However, we do not know whether GR is behind the physics governing stronger gravitational field regimes, such as near neutron stars or massive black-holes (MBHs). Gravitational-wave (GW) astronomy is a promising tool to test and validate GR and/or potential alternative theories of gravity. The information that a GW waveform carries not only will allow us to map the strong gravitational field of its source, but also determine the theory of gravity ruling its dynamics. In this work, we explore the extent to which we could distinguish between GR and other theories of gravity through the detection of low-frequency GWs from extreme-mass-ratio inspirals (EMRIs) and, in particular, we focus on dynamical Chern-Simons modified gravity (DCSMG). To that end, we develop a framework that enables us, for the first time, to perform a parameter estimation analysis for EMRIs in DCSMG. Our model is described by a 15-dimensional parameter space, that includes the Chern-Simons (CS) parameter which characterises the deviation between the two theories, and our analysis is based on Fisher information matrix techniques together with a (maximum-mismatch) criterion to assess the validity of our results. In our analysis, we study a 5-dimensional parameter space, finding that a GW detector like the Laser Interferometer Space Antenna (LISA) or eLISA (evolved LISA) should be able to discriminate between GR and DCSMG with fractional errors below 5%, and hence place bounds four orders of magnitude better than current Solar System bounds.

#### Sep 12, 2012

1209.2534 (/preprints)
2012-09-12, 19:27 

## [1209.1722] Spin-dominated waveforms for unequal mass compact binaries

Authors: M&#xe1;rton T&#xe1;pai, Zolt&#xe1;n Keresztes, L&#xe1;szl&#xf3; &#xc1;rp&#xe1;d Gergely

Date: 8 Sep 2012

Abstract: We derive spin-dominated waveforms (SDW) for binary systems composed of spinning black holes with unequal masses (less than 1:30). Such systems could be formed by an astrophysical black hole with a smaller black hole or a neutron star companion; and typically arise for supermassive black hole encounters. SDW characterize the last stages of the inspiral, when the larger spin dominates over the orbital angular momentum (while the spin of the smaller companion can be neglected). They emerge as a double expansion in the post-Newtonian parameter $\varepsilon$ and the ratio $\xi$ of the orbital angular momentum and dominant spin. The SDW amplitudes are presented to ($\varepsilonˆ{3/2},\xi$) orders, while the phase of the gravitational waves to ($\varepsilonˆ{2},\xi$) orders (omitting the highest order mixed terms). To this accuracy the amplitude includes the (leading order) spin-orbit contributions, while the phase the (leading order) spin-orbit, self-spin and mass quadrupole-monopole contributions. While the SDW hold for any mass ratio smaller than 1:30, lower bounds for the mass ratios are derived from the best sensitivity frequency range expected for Advanced LIGO (giving 1:140), the Einstein Telescope ($7\times 10ˆ{-4}$), the LAGRANGE ($7\times 10ˆ{-7}$) and LISA missions ($7\times 10ˆ{-9}$), respectively.

#### Sep 10, 2012

1209.1722 (/preprints)
2012-09-10, 22:19 

## [1208.3038] Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes III. Quasinormal Pulsations of Schwarzschild and Kerr Black Holes

Authors: David A. Nichols, Aaron Zimmerman, Yanbei Chen, Geoffrey Lovelace, Keith D. Matthews, Robert Owen, Fan Zhang, Kip S. Thorne

Date: 15 Aug 2012

Abstract: In recent papers, we and colleagues have introduced a way to visualize the full vacuum Riemann curvature tensor using frame-drag vortex lines and their vorticities, and tidal tendex lines and their tendicities. We have also introduced the concepts of horizon vortexes and tendexes and 3-D vortexes and tendexes (regions where vorticities or tendicities are large). Using these concepts, we discover a number of previously unknown features of quasinormal modes of Schwarzschild and Kerr black holes. These modes can be classified by mode indexes (n,l,m), and parity, which can be electric [(-1)ˆl] or magnetic [(-1)ˆ(l+1)]. Among our discoveries are these: (i) There is a near duality between modes of the same (n,l,m): a duality in which the tendex and vortex structures of electric-parity modes are interchanged with the vortex and tendex structures (respectively) of magnetic-parity modes. (ii) This near duality is perfect for the modes' complex eigenfrequencies (which are well known to be identical) and perfect on the horizon; it is slightly broken in the equatorial plane of a non-spinning hole, and the breaking becomes greater out of the equatorial plane, and greater as the hole is spun up; but even out of the plane for fast-spinning holes, the duality is surprisingly good. (iii) Electric-parity modes can be regarded as generated by 3-D tendexes that stick radially out of the horizon. As these "longitudinal," near-zone tendexes rotate or oscillate, they generate longitudinal-transverse near-zone vortexes and tendexes, and outgoing and ingoing gravitational waves. The ingoing waves act back on the longitudinal tendexes, driving them to slide off the horizon, which results in decay of the mode's strength. (iv) By duality, magnetic-parity modes are driven in this same manner by longitudinal, near-zone vortexes that stick out of the horizon. [Abstract abridged.]

#### Aug 15, 2012

1208.3038 (/preprints)
2012-08-15, 22:35 

## [1208.3034] Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes II. Stationary Black Holes

Authors: Fan Zhang, Aaron Zimmerman, David A. Nichols, Yanbei Chen, Geoffrey Lovelace, Keith D. Matthews, Robert Owen, Kip S. Thorne

Date: 15 Aug 2012

Abstract: When one splits spacetime into space plus time, the Weyl curvature tensor (which equals the Riemann tensor in vacuum) splits into two spatial, symmetric, traceless tensors: the tidal field $E$, which produces tidal forces, and the frame-drag field $B$, which produces differential frame dragging. In recent papers, we and colleagues have introduced ways to visualize these two fields: tidal tendex lines (integral curves of the three eigenvector fields of $E$) and their tendicities (eigenvalues of these eigenvector fields); and the corresponding entities for the frame-drag field: frame-drag vortex lines and their vorticities. These entities fully characterize the vacuum Riemann tensor. In this paper, we compute and depict the tendex and vortex lines, and their tendicities and vorticities, outside the horizons of stationary (Schwarzschild and Kerr) black holes; and we introduce and depict the black holes' horizon tendicity and vorticity (the normal-normal components of $E$ and $B$ on the horizon). For Schwarzschild and Kerr black holes, the horizon tendicity is proportional to the horizon's intrinsic scalar curvature, and the horizon vorticity is proportional to an extrinsic scalar curvature. We show that, for horizon-penetrating time slices, all these entities ($E$, $B$, the tendex lines and vortex lines, the lines' tendicities and vorticities, and the horizon tendicities and vorticities) are affected only weakly by changes of slicing and changes of spatial coordinates, within those slicing and coordinate choices that are commonly used for black holes. [Abstract is abbreviated.]

#### Aug 15, 2012

1208.3034 (/preprints)
2012-08-15, 22:35 

## [1208.2340] The multi-detector F-statistic metric for short-duration non-precessing inspiral gravitational-wave signals

Authors: Drew Keppel

Date: 11 Aug 2012

Abstract: We derive explicit expressions for the multi-detector F-statistic metric applied to short-duration non-precessing inspiral signals. This is required for template bank production associated with coherent searches for short-duration non-precessing inspiral signals in gravitational-wave data from a network of detectors. We compare the metric's performance with explicit overlap calculations for all relevant dimensions of parameter space and find the metric accurately predicts the loss of detection statistic above overlaps of 95%. We also show the effect that neglecting the variations of the detector response functions has on the metric.

#### Aug 13, 2012

1208.2340 (/preprints)
2012-08-13, 22:46 

## [1208.2007] A Novel Universal Statistic for Computing Upper Limits in Ill-behaved Background

Date: 9 Aug 2012

Abstract: Analysis of experimental data must sometimes deal with abrupt changes in the distribution of measured values. Setting upper limits on signals usually involves a veto procedure that excludes data not described by an assumed statistical model. We show how to implement statistical estimates of physical quantities (such as upper limits) that are valid without assuming a particular family of statistical distributions, while still providing close to optimal values when the data is from an expected distribution (such as Gaussian or exponential). This new technique can compute statistically sound results in the presence of severe non-Gaussian noise, relaxes assumptions on distribution stationarity and is especially useful in automated analysis of large datasets, where computational speed is important.

#### Aug 10, 2012

1208.2007 (/preprints)
2012-08-10, 09:01 

## [1207.7176] Einstein@Home all-sky search for periodic gravitational waves in LIGO S5 data

Date: 31 Jul 2012

Abstract: This paper presents results of an all-sky searches for periodic gravitational waves in the frequency range [50, 1190] Hz and with frequency derivative ranges of [-2 \times 10ˆ-9, 1.1 \times 10ˆ-10] Hz/s for the fifth LIGO science run (S5). The novelty of the search lies in the use of a non-coherent technique based on the Hough-transform to combine the information from coherent searches on timescales of about one day. Because these searches are very computationally intensive, they have been deployed on the Einstein@Home distributed computing project infrastructure. The search presented here is about a factor 3 more sensitive than the previous Einstein@Home search in early S5 LIGO data. The post-processing has left us with eight surviving candidates. We show that deeper follow-up studies rule each of them out. Hence, since no statistically significant gravitational wave signals have been detected, we report upper limits on the intrinsic gravitational wave amplitude h0. For example, in the 0.5 Hz-wide band at 152.5 Hz, we can exclude the presence of signals with h0 greater than 7.6 \times 10ˆ-25 with a 90% confidence level.

#### Jul 31, 2012

1207.7176 (/preprints)
2012-07-31, 20:57 

## [1207.6961] Aligned Spins: Orbital Elements, Decaying Orbits, and Last Stable Circular Orbit to high post-Newtonian Orders

Authors: Manuel Tessmer, Johannes Hartung, Gerhard Sch&#xe4;fer

Date: 30 Jul 2012

Abstract: In this article the quasi-Keplerian parameterisation for the case that spins and orbital angular momentum in a compact binary system are aligned or anti-aligned with the orbital angular momentum vector is extended to 3PN point-mass, next-to-next-to-leading order spin-orbit, next-to-next-to-leading order spin(1)-spin(2), and next-to-leading order spin-squared dynamics in the conservative regime. In a further step, we use the expressions for the radiative multipole moments with spin to leading order linear and quadratic in both spins to compute radiation losses of the orbital binding energy and angular momentum. Orbital averaged expressions for the decay of energy and eccentricity are provided. An expression for the last stable circular orbit is given in terms of the angular velocity type variable $x$.

#### Jul 30, 2012

1207.6961 (/preprints)
2012-07-30, 20:47 

## [1207.6755] Galactic Center Research: Manifestations of the Central Black Hole

Authors: Mark Morris, Leo Meyer, Andrea Ghez

Date: 29 Jul 2012

Abstract: This review summarizes a few of the frontiers of Galactic center research that are currently the focus of considerable activity and attention. It is aimed at providing a necessarily incomplete sketch of some of the timely work being done on phenomena taking place in, or originating in, the central few parsecs of the Galaxy, with particular attention to topics related to the Galactic black hole (GBH). We have chosen to expand on the following exciting topics: 1) the characterization and the implications for the variability of emission from the GBH, 2) the strong evidence for a powerful X-ray flare in the Galactic center within the past few hundred years, and the likelihood that the GBH is implicated in that event, 3) the prospects for detecting the "shadow" of the GBH, 4) an overview of the current state of research on the central S-star cluster, and what has been learned from the stellar orbits within that cluster, and 5) the current hypotheses for the origin of the G2 dust cloud that is projected to make a close passage by the GBH in 2013.

#### Jul 30, 2012

1207.6755 (/preprints)
2012-07-30, 20:46 

## [1207.6406] Detecting binary neutron star systems with spin in advanced gravitational-wave detectors

Authors: Duncan A. Brown, Ian Harry, Andrew Lundgren, Alexander H. Nitz

Date: 26 Jul 2012

Abstract: The detection of gravitational waves from binary neutron stars is a major goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo. Previous searches for binary neutron stars with LIGO and Virgo neglected the component stars' angular momentum (spin). We demonstrate that neglecting spin in matched-filter searches causes advanced detectors to lose more than 3% of the possible signal-to-noise ratio for 59% (6%) of sources, assuming that neutron star dimensionless spins, $cJ/GMˆ2$, are uniformly distributed with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have isotropically distributed spin orientations. We present a new method of constructing filter banks for advanced-detector searches, which can create template banks of signals with non-zero spins that are (anti-)aligned with the orbital angular momentum. We show that this search loses more than 3% of the maximium signal-to-noise for only 9% (0.2%) of BNS sources with dimensionless spins between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template bank will prevent selection bias in gravitational-wave searches and allow a more accurate exploration of the distribution of spins in binary neutron stars.

#### Jul 29, 2012

1207.6406 (/preprints)
2012-07-29, 23:25 

## [1207.6401] Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events

Authors: Michael Kesden

Date: 26 Jul 2012

Abstract: A star orbiting a supermassive black hole can be tidally disrupted if the black hole's gravitational tidal field exceeds the star's self gravity at pericenter. Some of stellar tidal debris can become gravitationally bound to the black hole and be subsequently accreted, leading to a bright electromagnetic flare. In the Newtonian limit, this flare will have a light curve that scales as tˆ-5/3 if the tidal debris has a flat distribution in binding energy. We investigate the time dependence of the black-hole mass accretion rate when tidal disruption occurs close enough the black hole that relativistic effects are significant. We find that for orbits with pericenters comparable to the radius of the marginally bound circular orbit, relativistic effects can double the peak accretion rate and halve the time it takes to reach this peak accretion rate. The accretion rate depends on both the magnitude of the black-hole spin and its orientation with respect to the stellar orbit; for orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal black-hole spin anti-aligned with the orbital angular momentum leads to the largest peak accretion rate.

#### Jul 29, 2012

1207.6401 (/preprints)
2012-07-29, 23:25 

## [1207.5595] EMRI corrections to the angular velocity and redshift factor of a mass in circular orbit about a Kerr black hole

Authors: Abhay G. Shah, John L. Friedman, Tobias S. Keidl

Date: 24 Jul 2012

Abstract: This is the first of two papers on computing the self-force in a radiation gauge for a particle moving in circular, equatorial orbit about a Kerr black hole. In the EMRI (extreme-mass-ratio inspiral) framework, with mode-sum renormalization, we compute the renormalized value of the quantity $h_{\alpha\beta}uˆ\alpha uˆ\beta$, gauge-invariant under gauge transformations generated by a helically symmetric gauge vector; and we find the related order $\frak{m}$ correction to the particle's angular velocity at fixed renormalized redshift (and to its redshift at fixed angular velocity). The radiative part of the perturbed metric is constructed from the Hertz potential which is extracted from the Weyl scalar by an algebraic inversion\cite{sf2}. We then write the spin-weighted spheroidal harmonics as a sum over spin-weighted spherical harmonics and use mode-sum renormalization to find the renormalization coefficients by matching a series in $L=\ell+½$ to the large-$L$ behavior of the expression for $H := \frac12 h_{\alpha\beta}uˆ\alpha uˆ\beta$. The non-radiative parts of the perturbed metric associated with changes in mass and angular momentum are calculated in the Kerr gauge.

#### Jul 28, 2012

1207.5595 (/preprints)
2012-07-28, 09:44 

## [1207.5645] Observing the dynamics of super-massive black hole binaries with Pulsar Timing Arrays

Authors: C. M. F. Mingarelli, K. Grover, T. Sidery, R. J. E. Smith, A. Vecchio

Date: 24 Jul 2012

Abstract: Pulsar Timing Arrays are a prime tool to study unexplored astrophysical regimes with gravitational waves. Here we show that the detection of gravitational radiation from individually resolvable super-massive black hole binary systems can yield direct information about the masses and spins of the black holes, provided that the gravitational-wave induced timing fluctuations both at the pulsar and at the Earth are detected. This in turn provides a map of the non-linear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of super-massive black holes. We discuss the potential, the challenges and the limitations of these observations.

#### Jul 28, 2012

1207.5645 (/preprints)
2012-07-28, 09:44 

## [1207.6304] Black Hole-Neutron Star Mergers: Disk Mass Predictions

Authors: Francois Foucart

Date: 26 Jul 2012

Abstract: Determining the final result of black hole-neutron star mergers, and in particular the amount of matter remaining outside the black hole at late times, has been one of the main motivations behind the numerical simulation of these systems. Black hole-neutron star binaries are amongst the most likely progenitors of short gamma-ray bursts — as long as they result in the formation of massive (at least ~0.1 solar mass) accretion disks around the black hole. Whether this actually happens strongly depends on the physical characteristics of the system, and in particular on the mass ratio, the spin of the black hole, and the radius of the neutron star. We present here a simple two-parameter model, fitted to existing numerical results, for the determination of the mass remaining outside the black hole a few milliseconds after a black hole-neutron star merger. This model predicts the remnant mass within a few percents of the mass of the neutron star, at least for remnant masses up to 20% of the neutron star mass. Results across the range of parameters deemed to be the most likely astrophysically are presented here. We find that, for 10 solar mass black holes, massive disks are only possible for fairly large neutron stars (R>12km), or quasi-extremal black hole spins (a/M>0.9). We also use our model to discuss how the equation of state of the neutron star affects the final remnant, and the strong influence that this can have on the rate of short gamma-ray bursts produced by black hole-neutron star mergers.

#### Jul 26, 2012

1207.6304 (/preprints)
2012-07-26, 23:38 

## [1207.5410] Testing gravitational theories using Eccentric Eclipsing Detached Binaries

Authors: Mariafelicia De Laurentis, Rosario De Rosa, Fabio Garufi, Leopoldo Milano

Date: 23 Jul 2012

Abstract: In this paper we compare the effects of different theories of gravitation on the apsidal motion of a sample of Eccentric Eclipsing Detached Binary stars. The comparison is performed by using the formalism of the Post-Newtonian parametrization to calculate the theoretical advance at periastron and compare it to the observed one, after having considered the effects of the structure and rotation of the involved stars. A variance analysis on the results of this comparison, shows that no significant difference can be found due to the effect of the different theories under test with respect to the standard General Relativity. It will be possible to observe differences, as we would expect, by checking the observed period variation on a much larger lapse of time. It can also be noticed from our results, that f(R) theory is the nearest to GR with respect to the other tested theories.

#### Jul 23, 2012

1207.5410 (/preprints)
2012-07-23, 23:09 

## [1207.5359] Gravitational wave energy spectrum of hyperbolic encounters

Authors: Lorenzo De Vittori, Philippe Jetzer, Antoine Klein

Date: 23 Jul 2012

Abstract: The emission of gravitational waves is studied for a system of massive objects interacting on hyperbolic orbits within the quadrupole approximation following the work of Capozziello et al. Here we focus on the derivation of an analytic formula for the energy spectrum of the emitted waves. We checked numerically that our formula is in agreement with the two limiting cases for which results were already available: for the eccentricity {\epsilon} = 1, the parabolic case whose spectrum was computed by Berry and Gair, and the large {\epsilon} limit with the formula given by Turner.

#### Jul 23, 2012

1207.5359 (/preprints)
2012-07-23, 23:09 

## [1207.5448] Towards the 4th post-Newtonian Hamiltonian for two-point-mass systems

Authors: Piotr Jaranowski, Gerhard Sch&#xe4;fer

Date: 23 Jul 2012

Abstract: The article presents the conservative dynamics of gravitationally interacting two-point-mass systems up to the eight order in the inverse power of the velocity of light, i.e.\ 4th post-Newtonian (4PN) order, and up to quadratic order in Newton's gravitational constant. Additionally, all logarithmic terms at the 4PN order are given as well as terms describing the test-mass limit. With the aid of the Poincaré algebra additional terms are obtained. The dynamics is presented in form of an autonomous Hamiltonian derived within the formalism of Arnowitt, Deser and Misner. Out of the 57 different terms of the 4PN Hamiltonian in the center-of-mass frame, the coefficients of 45 of them are derived. Reduction of the obtained results to circular orbits is performed resulting in the 4PN-accurate formula for energy expressed in terms of angular frequency in which two coefficients are obtained for the first time.

#### Jul 23, 2012

1207.5448 (/preprints)
2012-07-23, 23:08 

## [1207.3361] Systematic errors in measuring parameters of non-spinning compact binary coalescences with post-Newtonian templates

Authors: Sukanta Bose, Shaon Ghosh, Ajith Parameswaran

Date: 13 Jul 2012

Abstract: We study the astrophysical impact of inaccurate and incomplete modeling of the gravitational waveforms from compact binary coalescences (CBCs). We do so by the matched filtering of complete inspiral-merger-ringdown (IMR) signals with a bank of inspiral-phase templates modeled after the 3.5 post-Newtonian TaylorT1 approximant. The rationale for the choice of the templates is threefold: (1) The inspiral phase of the Phenomenological signals, which are an example of complete IMR signals, is modeled on the same TaylorT1 approximant. (2) In the low-mass limit, where the merger and ringdown phases last much shorter than the inspiral phase, the errors should tend to vanishingly small values and, thus, provide an important check on the numerical aspects of our simulations. (3) Since the binary black hole (BBH) signals are not yet known for mass-ratios above ten and since signals from CBCs involving neutron stars are affected by uncertainties in the knowledge of their equation of state, inspiral templates are still in use in searches for those signals. The results from our numerical simulations are compared with analytical calculations of the systematic errors using the Fisher matrix on the template parameter space. We find that the loss in signal-to-noise ratio (SNR) can be as large as 60% even for binary black holes with component masses m1 = 13M\odot and m2 = 20M\odot. Also, the estimated total-mass for the same pair can be off by as much as 20%. Both of these are worse for some higher-mass combinations. Even the estimation of the symmetric mass-ratio {\eta} suffers a nearly 20% error for this example, and can be worse than 50% for the mass ranges studied here. These errors significantly dominate their statistical counterparts (at a nominal SNR of 10). It may, however, be possible to mitigate the loss in SNR by allowing for templates with unphysical values of {\eta}.

#### Jul 23, 2012

1207.3361 (/preprints)
2012-07-23, 11:53 

## [1207.4956] EMRI data analysis with a phenomenological waveform

Authors: Yan Wang, Yu Shang, Stanislav Babak

Date: 20 Jul 2012

Abstract: Extreme mass ratio inspirals (EMRIs) (capture and inspiral of a compact stellar mass object into a Massive Black Hole (MBH)) are among the most interesting objects for the gravitational wave astronomy. It is a very challenging task to detect those sources with the accurate estimation parameters of binaries primarily due to a large number of the secondary maxima on the likelihood surface. Search algorithms based on the matched filtering require computation of the gravitational waveform hundreds of thousands of times, which is currently not feasible with the most accurate (faithful) models of EMRIs. Here we propose to use a phenomenological template family which covers a large range of EMRIs parameter space. We use these phenomenological templates to detect the signal in the simulated data and then, assuming a particular EMRI model, estimate the physical parameters of the binary. We have separated the detection problem, which is done in a model-independent way, from the parameter estimation. For the latter one, we need to adopt the model for inspiral in order to map phenomenological parameters onto the physical parameter characterizing EMRIs.

#### Jul 23, 2012

1207.4956 (/preprints)
2012-07-23, 08:26 

## [1207.4848] Prospects for observing ultra-compact binaries with space-based gravitational wave interferometers and optical telescopes

Authors: Tyson B. Littenberg, Shane L. Larson, Gijs Nelemans, Neil J. Cornish

Date: 20 Jul 2012

Abstract: Space-based gravitational wave interferometers are sensitive to the galactic population of ultra-compact binaries. An important subset of the ultra-compact binary population are those stars that can be individually resolved by both gravitational wave interferometers and electromagnetic telescopes. The aim of this paper is to quantify the multi-messenger potential of space-based interferometers with arm-lengths between 1 and 5 Gm. The Fisher Information Matrix is used to estimate the number of binaries from a model of the Milky Way which are localized on the sky by the gravitational wave detector to within 1 deg$ˆ2$ and bright enough to be detected by a magnitude limited survey. We find, depending on the choice of GW detector characteristics, limiting magnitude, and observing strategy, that up to a few hundred gravitational wave sources could be detected in electromagnetic follow-up observations.

#### Jul 23, 2012

1207.4848 (/preprints)
2012-07-23, 08:26 

## [1207.4759] Testing general relativity with gravitational waves: a reality check

Authors: Michele Vallisneri

Date: 19 Jul 2012

Abstract: The observations of gravitational-wave signals from astrophysical sources such as binary inspirals will be used to test general relativity for self consistency and against alternative theories of gravity. I describe a simple formula that can be used to characterize the prospects of such tests, by estimating the matched-filtering signal-to-noise ratio required to detect non-general-relativistic corrections of a given magnitude. The formula is valid for sufficiently strong signals; it requires the computation of a single number (the fitting factor between the general-relativistic and corrected waveform families); and it can be applied to all tests that embed general-relativity in a larger theory, including tests of individual theories such as Brans--Dicke gravity, as well as the phenomenological schemes that introduce corrections and extra terms in the post-Newtonian phasing expressions of inspiral waveforms. Using the formula, I show on very general grounds that the volume-limited gravitational-wave searches performed with second-generation ground-based detectors would detect alternative-gravity corrections to general-relativistic waveforms as small as 1--10% (i.e., fitting factors of 0.9 to 0.99).

#### Jul 19, 2012

1207.4759 (/preprints)
2012-07-19, 21:45 

## [1207.4253] Quasinormal-mode spectrum of Kerr black holes and its geometric interpretation

Authors: Huan Yang, David A. Nichols, Fan Zhang, Aaron Zimmerman, Zhongyang Zhang, Yanbei Chen

Date: 18 Jul 2012

Abstract: There is a well-known, intuitive geometric correspondence between high-frequency QNMs of Schwarzschild black holes and null geodesics that reside on the light-ring : the real part of the mode's frequency relates to the geodesic's orbital frequency, and the imaginary part of the frequency corresponds to the Lyapunov exponent of the orbit. For slowly rotating black holes, the QNM real frequency is a linear combination of a the orbit's precessional and orbital frequencies, but the correspondence is otherwise unchanged. In this paper, we find a relationship between the QNM frequencies of Kerr black holes of arbitrary (astrophysical) spins and general spherical photon orbits, which is analogous to the relationship for slowly rotating holes. To derive this result, we first use the WKB approximation to compute accurate algebraic expressions for large-l QNM frequencies. Comparing our WKB calculation to the leading-order, geometric-optics approximation to scalar-wave propagation in the Kerr spacetime, we then draw a correspondence between the real parts of the parameters of a QNM and the conserved quantities of spherical photon orbits. At next-to-leading order in this comparison, we relate the imaginary parts of the QNM parameters to coefficients that modify the amplitude of the scalar wave. With this correspondence, we find a geometric interpretation to two features of the QNM spectrum of Kerr black holes: First, for Kerr holes rotating near the maximal rate, a large number of modes have nearly zero damping; we connect this characteristic to the fact that a large number of spherical photon orbits approach the horizon in this limit. Second, for black holes of any spins, the frequencies of specific sets of modes are degenerate; we find that this feature arises when the spherical photon orbits corresponding to these modes form closed (as opposed to ergodically winding) curves.

#### Jul 18, 2012

1207.4253 (/preprints)
2012-07-18, 18:55 

## [1207.3805] Gravitational Waves from Fallback Accretion onto Neutron Stars

Authors: Anthony L. Piro (Caltech), Eric Thrane (University of Minnesota)

Date: 16 Jul 2012

Abstract: Massive stars generally end their lives as neutron stars (NSs) or black holes (BHs), with NS formation typically occurring at the low mass end and collapse to a BH more likely at the high mass end. In an intermediate regime, with a mass range that depends on the uncertain details of rotation and mass loss during the star's life, a NS is initially formed which then experiences fallback accretion and collapse to a BH. The electromagnetic consequence of such an event is not clear. Depending on the progenitor's structure, possibilities range from a long gamma-ray burst to a Type II supernova (that may or may not be jet-powered) to a collapse with a weak electromagnetic signature. Gravitational waves (GWs) provide the exciting opportunity to peer through the envelope of a dying massive star and directly probe what is occurring inside. We explore whether fallback onto young NSs can be detected by ground-based interferometers. When the incoming material has sufficient angular momentum to form a disk, the accretion spins up the NS sufficiently to produce non-axisymmetric instabilities and gravitational radiation at frequencies of ~700-2400 Hz for ~30-3000 s until collapse to a BH occurs. Using a realistic excess cross-power search algorithm, we show that such events are detectable by Advanced LIGO out to ~17 Mpc. From the rate of nearby core-collapse supernovae, we estimate that there will be ~1-2 events each year that are worth checking for fallback GWs. The observation of these unique GW signatures coincident with electromagnetic detections would identify the transient events that are associated with this channel of BH formation, while providing information about the protoneutron star progenitor.

#### Jul 17, 2012

1207.3805 (/preprints)
2012-07-17, 18:49 

## [1207.3088] Towards models of gravitational waveforms from generic binaries: A simple approximate mapping between precessing and non-precessing inspiral signals

Authors: Patricia Schmidt, Mark Hannam, Sascha Husa

Date: 12 Jul 2012

Abstract: One of the greatest theoretical challenges in the build-up to the era of second-generation gravitational-wave detectors is the modeling of generic binary waveforms. We introduce an approximation that has the potential to significantly simplify this problem. We show that generic precessing-binary inspiral waveforms (covering a seven-dimensional parameter space) can be mapped to only a two-dimensional space of non-precessing binaries, characterized by the mass ratio and a single effective total spin. The mapping consists of a time-dependent rotation of the waveforms into the quadrupole-aligned frame, and is extremely accurate (matches $> 0.99$ with parameter biases in the total spin of $\Delta \chi \leq 0.04$), even in the case of transitional precession. In addition, we demonstrate a simple method to construct hybrid post-Newtonian--numerical-relativity precessing-binary waveforms in the quadrupole-aligned frame, and provide evidence that our approximate mapping can be used all the way to the merger. Finally, based on these results, we outline a general proposal for the construction of generic waveform models, which will be the focus of future work.

#### Jul 16, 2012

1207.3088 (/preprints)
2012-07-16, 00:34 

## [1207.2839] Self Force Orbit-Integrated gravitational waveforms for E(I)MRIs

Authors: Lior M. Burko, Kristen A. Lackeos

Date: 12 Jul 2012

Abstract: We present the first orbit-integrated self force effects for an IMRI or EMRI source, specifically the effects of its conservative piece on the orbit and on the waveform. We consider the quasi-circular motion of a particle in the spacetime of a Schwarzschild black hole, find the orbit and the corresponding gravitational waveform, and discuss the importance of the conservative piece of the self force in detection and parameter estimation. We also show the effect of the conservative piece of the self force on gauge invariant quantities, specifically $uˆt$ as a function of the angular frequency $\Omega$. For long templates the inclusion of the conservative piece is crucial for gravitational-wave astronomy, yet may be ignored for short templates with little effect on detection rate.

#### Jul 12, 2012

1207.2839 (/preprints)
2012-07-12, 23:10 

## [1207.2497] Constraining Intermediate-Mass Black Holes in Globular Clusters

Authors: Stefan Umbreit, Frederic A. Rasio

Date: 10 Jul 2012

Abstract: Decades after the first predictions of intermediate-mass black holes (IMBHs) in globular clusters (GCs) there is still no unambiguous observational evidence for their existence. The most promising signatures for IMBHs are found in the cores of GCs, where the evidence now comes from the stellar velocity distribution, the surface density profile, and, for very deep observations, the mass-segregation profile near the cluster center. However, interpretation of the data, and, in particular, constraints on central IMBH masses, require the use of detailed cluster dynamical models. Here we present results from Monte Carlo cluster simulations of GCs that harbor IMBHs. As an example of application, we compare velocity dispersion, surface brightness and mass-segregation profiles with observations of the GC M10, and constrain the mass of a possible central IMBH in this cluster. We find that, although M10 does not seem to possess a cuspy surface density profile, the presence of an IMBH with a mass up to 0.75% of the total cluster mass, corresponding to about 600 Msun, cannot be excluded. This is also in agreement with the surface brightness profile, although we find it to be less constraining, as it is dominated by the light of giants, causing it to fluctuate significantly. We also find that the mass-segregation profile cannot be used to discriminate between models with and without IMBH. The reason is that M10 is not yet dynamically evolved enough for the quenching of mass segregation to take effect. Finally, detecting a velocity dispersion cusp in clusters with central densities as low as in M10 is extremely challenging, and has to rely on only 20-40 bright stars. It is only when stars with masses down to 0.3 Msun are included that the velocity cusp is sampled close enough to the IMBH for a significant increase above the core velocity dispersion to become detectable.

#### Jul 11, 2012

1207.2497 (/preprints)
2012-07-11, 23:12 

## [1207.0769] Horizon-absorption effects in coalescing black-hole binaries: An effective-one-body study of the non-spinning case

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Anil Zenginoglu

Date: 3 Jul 2012

Abstract: We study the horizon absorption of gravitational waves in coalescing, circularized, nonspinning black hole binaries. The horizon absorbed fluxes of a binary with a large mass ratio (q=1000) obtained by numerical perturbative simulations are compared with an analytical, effective-one-body (EOB) resummed expression recently proposed. The perturbative method employs an analytical, linear in the mass ratio, effective-one-body (EOB) resummed radiation reaction, and the Regge-Wheeler-Zerilli (RWZ) formalism for wave extraction. Hyperboloidal (transmitting) layers are employed for the numerical solution of the RWZ equations to accurately compute horizon fluxes up to the late plunge phase. The horizon fluxes from perturbative simulations and the EOB-resummed expression agree at the level of a few percent down to the late plunge. An upgrade of the EOB model for nonspinning binaries that includes horizon absorption of angular momentum as an additional term in the resummed radiation reaction is then discussed. The effect of this term on the waveform phasing for binaries with mass ratios spanning 1 to 1000 is investigated. We confirm that for comparable and intermediate-mass-ratio binaries horizon absorbtion is practically negligible for detection with advanced LIGO and the Einstein Telescope (faithfulness greater than or equal to 0.997).

#### Jul 05, 2012

1207.0769 (/preprints)
2012-07-05, 09:27 

## [1207.0001] Gravitational waves from spinning eccentric binaries

Authors: P&#xe9;ter Csizmadia, Gergely Debreczeni, Istv&#xe1;n R&#xe1;cz, M&#xe1;ty&#xe1;s Vas&#xfa;th

Date: 29 Jun 2012

Abstract: This paper is to introduce a new software called CBwaves which provides a fast and accurate computational tool to determine the gravitational waveforms yielded by generic spinning binaries of neutron stars and/or black holes on eccentric orbits. This is done within the post-Newtonian (PN) framework by integrating the equations of motion and the spin precession equations while the radiation field is determined by a simultaneous evaluation of the analytic waveforms. In applying CBwaves various physically interesting scenarios have been investigated. In particular, we have studied the appropriateness of the adiabatic approximation, and justified that the energy balance relation is indeed insensitive to the specific form of the applied radiation reaction term. By studying eccentric binary systems it is demonstrated that circular template banks are very ineffective in identifying binaries even if they possess tiny residual orbital eccentricity. In addition, by investigating the validity of the energy balance relation we show that, on contrary to the general expectations, the post-Newtonian approximation should not be applied once the post-Newtonian parameter gets beyond the critical value $\sim 0.08-0.1$. Finally, by studying the early phase of the gravitational waves emitted by strongly eccentric binary systems — which could be formed e.g. in various many-body interactions in the galactic halo — we have found that they possess very specific characteristics which may be used to identify these type of binary systems.

#### Jul 02, 2012

1207.0001 (/preprints)
2012-07-02, 22:10 

## [1206.7087] The dynamics of the gravitational two-body problem in the post-Newtonian approximation at quadratic order in the Newton's constant

Authors: Stefano Foffa, Riccardo Sturani

Date: 29 Jun 2012

Abstract: We derive the conservative part of the Lagrangian and the energy of a gravitationally bound two-body system at fourth post-Newtonian order, up to terms quadratic in the Newton's constant. We also show that such terms are compatible with Lorentz invariance and we write an ansatz for the center-of mass position. The remaining terms carrying higher powers of the Newton constant are currently under investigation.

#### Jul 01, 2012

1206.7087 (/preprints)
2012-07-01, 22:40 

## [1206.6538] Nonlinear gravitational self-force. I. Field outside a small body

Date: 27 Jun 2012

Abstract: A small extended body moving through an external spacetime $g_{\alpha\beta}$ creates a metric perturbation $h_{\alpha\beta}$, which forces the body away from geodesic motion in $g_{\alpha\beta}$. The foundations of this effect, called the gravitational self-force, are now well established, but concrete results have mostly been limited to linear order. Accurately modeling the dynamics of compact binaries requires proceeding to nonlinear orders. To that end, I show how to obtain the metric perturbation outside the body at all orders in a class of generalized wave gauges. In a small buffer region surrounding the body, the form of the perturbation can be found analytically as an expansion for small distances $r$ from a representative worldline. Given only a specification of the body's multipole moments, the field obtained in the buffer region suffices to find the metric everywhere outside the body via a numerical puncture scheme. Following this procedure at first and second order, I calculate the field in the buffer region around an arbitrarily structured compact body at sufficiently high order in $r$ to numerically implement a second-order puncture scheme, including effects of the body's spin. I also define $n$th-order (local) generalizations of the Detweiler-Whiting singular and regular fields and show that in a certain sense, the body can be viewed as a skeleton of multipole moments.

#### Jun 28, 2012

1206.6538 (/preprints)
2012-06-28, 22:29 

## [1206.6163] Rapid alerts for following up gravitational wave event candidates

Authors: Peter S. Shawhan, for the LIGO Scientific Collaboration, Virgo Collaboration

Date: 27 Jun 2012

Abstract: Gravitational waves carry unique information about high-energy astrophysical events such as the inspiral and merger of neutron stars and black holes, core collapse in massive stars, and other sources. Large gravitational wave (GW) detectors utilizing exquisitely sensitive laser interferometry--namely, LIGO in the United States and GEO 600 and Virgo in Europe--have been successfully operated in recent years and are currently being upgraded to greatly improve their sensitivities. Many signals are expected to be detected in the coming decade. Simultaneous observing with the network of GW detectors enables us to identify and localize event candidates on the sky with modest precision, opening up the possibility of capturing optical transients or other electromagnetic counterparts to confirm an event and obtain complementary information about it. We developed and implemented the first complete low-latency GW data analysis and alert system in 2009-10 and used it to send alerts to several observing partners; the system design and some lessons learned are briefly described. We discuss several operational considerations and design choices for improving this scientific capability for future observations.

#### Jun 28, 2012

1206.6163 (/preprints)
2012-06-28, 10:16 

## [1206.6167] An upper limit to the velocity dispersion of relaxed stellar systems without massive black holes

Authors: M. Coleman Miller, Melvyn B. Davies

Date: 27 Jun 2012

Abstract: Massive black holes have been discovered in all closely examined galaxies with high velocity dispersion. The case is not as clear for lower-dispersion systems such as low-mass galaxies and globular clusters. Here we suggest that above a critical velocity dispersion of roughly 40 km/s, massive central black holes will form in relaxed stellar systems at any cosmic epoch. This is because above this dispersion primordial binaries cannot support the system against deep core collapse. If, as previous simulations show, the black holes formed in the cluster settle to produce a dense subcluster, then given the extremely high densities reached during core collapse the holes will merge with each other. For low velocity dispersions and hence low cluster escape speeds, mergers will typically kick out all or all but one of the holes due to three-body kicks or the asymmetric emission of gravitational radiation. If one hole remains, it will tidally disrupt stars at a high rate. If none remain, one is formed after runaway collisions between stars, then it tidally disrupts stars at a high rate. The accretion rate after disruption is many orders of magnitude above Eddington. If, as several studies suggest, the hole can accept matter at that rate because the generated radiation is trapped and advected, then it will grow quickly and form a massive central black hole.

#### Jun 28, 2012

1206.6167 (/preprints)
2012-06-28, 10:16 

## [1206.5331] Geometrical Aspects on Parameter estimation of stochastic gravitational wave background: beyond the Fisher analysis

Authors: Naoki Seto, Koutarou Kyutoku

Date: 22 Jun 2012

Abstract: The maximum likelihood method is often used for parameter estimation in gravitational wave astronomy. Recently, an interesting approach was proposed by Vallisneri to evaluate the distributions of parameter estimation errors expected for the method. This approach is to statistically analyze the local peaks of the likelihood surface, and works efficiently even for signals with low signal-to-noise ratios. Focusing special attention to geometric structure of the likelihood surface, we follow the proposed approach and derive formulae for a simplified model of data analysis where the target signal has only one intrinsic parameter, along with its overall amplitude. Then we apply our formulae to correlation analysis of stochastic gravitational wave background with a power-law spectrum. We report qualitative trends of the formulae using numerical results specifically obtained for correlation analysis with two Advanced-LIGO detectors.

#### Jun 27, 2012

1206.5331 (/preprints)
2012-06-27, 10:54 

## [1206.4722] Detection of pulsar beams deflected by the black hole in Sgr A*: effects of black hole spin

Authors: Sourabh Nampalliwar, Richard H. Price, Teviet Creighton, Fredrick A. Jenet

Date: 20 Jun 2012

Abstract: Some Galactic models predict a significant population of radio pulsars close to the our galactic center. Beams from these pulsars could get strongly deflected by the supermassive black hole (SMBH) believed to reside at the galactic center and reach the Earth. Earlier work assuming a Schwarzschild SMBH gave marginal chances of observing this exotic phenomenon with current telescopes and good chances with future telescopes. Here we calculate the odds of observability for a rotating SMBH. We find that the estimates of observation are not affected by the SMBH spin, but a pulsar timing analysis of deflected pulses might be able to provide an estimate of the spin of the central black hole.

#### Jun 26, 2012

1206.4722 (/preprints)
2012-06-26, 11:10 

## [1206.5531] Electron-phonon pairing mechanism: cuprates with high value of the critical temperature

Authors: R. Szcz\ke&#x15b;niak, A.P. Durajski

Date: 24 Jun 2012

Abstract: The model for the cuprates based on the modified electron-phonon pairing mechanism has been tested. For this purpose, the superconductors with high value of the critical temperature have been taken into consideration. In particular: ${\rm YBa_{2}Cu_{3}O_{7-y}}$, ${\rm HgBa_{2}CuO_{4+y}}$, ${\rm HgBa_{2}Cu_{1-x}Zn_{x}O_{4+y}}$, and ${\rm HgBa_{2}Ca_{2}Cu_{3}O_{8+y}}$. It has been shown that the dependence of the ratio $R_{1}\equiv 2\Delta_{tot}ˆ{(0)}/k_{B}T_{C}$ on the doping ($p$) can be properly predicted in the framework of the presented theory; the symbol $\Delta_{tot}ˆ{(0)}$ denotes the energy gap amplitude at the temperature of zero Kelvin, and $T_{C}$ is the critical temperature. The numerical results have been supplemented by the formula which describes the function $R_{1}(p)$.

#### Jun 26, 2012

1206.5531 (/preprints)
2012-06-26, 07:52 

## [1206.5786] Parameter estimation for inspiraling eccentric compact binaries including pericenter precession

Authors: Bal&#xe1;zs Mik&#xf3;czi, Bence Kocsis, P&#xe9;ter Forg&#xe1;cs, M&#xe1;ty&#xe1;s Vas&#xfa;th

Date: 25 Jun 2012

Abstract: Inspiraling supermassive black hole binary systems with high orbital eccentricity are important sources for space-based gravitational wave (GW) observatories like the Laser Interferometer Space Antenna (LISA). Eccentricity adds orbital harmonics to the Fourier-transform of the GW signal and relativistic pericenter precession leads to a three-way splitting of each harmonic peak. We study the parameter estimation accuracy for such waveforms with different initial eccentricity using the Fisher matrix method and a Monte Carlo sampling of the initial binary orientation. The eccentricity improves the parameter estimation by breaking degeneracies between different parameters. In particular, we find that the source localization precision improves significantly for higher mass binaries due to eccentricity. The typical sky position errors are $\sim1$deg for a nonspinning, $10ˆ7\,M_{\odot}$ equal mass binary at redshift $z=1$, if the initial eccentricity one year before merger is $e_0\sim 0.6$. Pericenter precession does not affect the source localization accuracy significantly, but it does further improve the mass and eccentricity estimation accuracy systematically by a factor of 3--10 for masses between $10ˆ6$ and $10ˆ7\,M_{\odot}$ for $e_0 \sim 0.3$.

#### Jun 25, 2012

1206.5786 (/preprints)
2012-06-25, 22:38 

## [1206.4949] Fundamental quantum optics experiments conceivable with satellites -- reaching relativistic distances and velocities

Authors: David Rideout, Thomas Jennewein, Giovanni Amelino-Camelia, Tommaso F. Demarie, Brendon L. Higgins, Achim Kempf, Adrian Kent, Raymond Laflamme, Xian Ma, Robert B. Mann, Eduardo Martin-Martinez, Nicolas C. Menicucci, John Moffat, Christoph Simon, Rafael Sorkin, Lee Smolin, Daniel R. Terno

Date: 21 Jun 2012

Abstract: Physical theories are developed to describe phenomena in particular regimes, and generally are valid only within a limited range of scales. For example, general relativity provides an effective description of the Universe at large length scales, and has been tested from the cosmic scale down to distances as small as 10 meters. In contrast, quantum theory provides an effective description of physics at small length scales. Direct tests of quantum theory have been performed at the smallest probeable scales at the Large Hadron Collider, ${\sim} 10ˆ{-20}$ meters, up to that of hundreds of kilometers. Yet, such tests fall short of the scales required to investigate potentially significant physics that arises at the intersection of quantum and relativistic regimes. We propose to push direct tests of quantum theory to larger and larger length scales, approaching that of the radius of curvature of spacetime, where we begin to probe the interaction between gravity and quantum phenomena. In particular, we review a wide variety of potential tests of fundamental physics that are conceivable with artificial satellites in Earth orbit and elsewhere in the solar system, and attempt to sketch the magnitudes of potentially observable effects. The tests have the potential to determine the applicability of quantum theory at larger length scales, eliminate various alternative physical theories, and place bounds on phenomenological models motivated by ideas about spacetime microstructure from quantum gravity. From a more pragmatic perspective, as quantum communication technologies such as quantum key distribution advance into Space towards large distances, some of the fundamental physical effects discussed here may need to be taken into account to make such schemes viable.

#### Jun 24, 2012

1206.4949 (/preprints)
2012-06-24, 22:55 

## [1206.5058] The Swift short gamma-ray burst rate density: prospects for detecting binary neutron star mergers by aLIGO

Authors: David Coward, Eric Howell, Tsvi Piran, Giulia Stratta, Marica Branchesi, Omer Bromberg, Bruce Gendre, Ronald Burman, Dafne Guetta

Date: 22 Jun 2012

Abstract: Presently only 30% of short gamma ray bursts (SGRBs) have accurate redshifts, and this sample is highly biased by the limited sensitivity of {\it Swift} to detect SGRBs. We account for the dominant biases to calculate a realistic SGRB rate density out to $z = 0.5$ using the {\it Swift} sample of peak fluxes, redshifts, and those SGRBs with a beaming angle constraint from X-ray/optical observations. Assuming a significant fraction of binary neutron star mergers produce SGRBs, we calculate lower and upper detection rate limits of (1-180) per Yr by an advanced LIGO and Virgo coincidence search. Our detection rate is compatible with extrapolations using Galactic pulsar observations and population synthesis.

#### Jun 24, 2012

1206.5058 (/preprints)
2012-06-24, 22:54 

## [1206.5229] Specialized Orthonormal Frames and Embedding

Authors: Frank B. Estabrook

Date: 22 Jun 2012

Abstract: We discuss specializations of the frames of flat orthonormal frame bundles over geometries of indefinite signature, and the resulting symmetries of families of imbedded Riemannian geometries; the embedding can be isometric, as in minimal surfaces or Regge-Teitelboim gravity, or torsion-free, as in Einstein vacuum gravity. Involutive Exterior Differential Systems (EDS) are given to express the well-posedness of the underlying partial differential embedding and specialization equations.

#### Jun 24, 2012

1206.5229 (/preprints)
2012-06-24, 22:54 

## [1206.4316] Resonant Post-Newtonian Eccentricity Excitation in Hierarchical Three-body Systems

Authors: Smadar Naoz, Bence Kocsis, Abraham Loeb, Nicolas Yunes

Date: 19 Jun 2012

Abstract: We study the secular, hierarchical three-body problem to first-order in a post-Newtonian expansion of General Relativity. We expand the first-order post-Newtonian Hamiltonian to leading-order in the ratio of the semi-major axis of the two orbits. In addition to the well-known terms that correspond to the GR precession of the inner and outer orbits, we find a new secular post-Newtonian interaction term that can affect the long-term evolution of the triple. We explore the parameter space for highly inclined and eccentric systems, where the Kozai-Lidov mechanism can produce large-amplitude oscillations in the eccentricities. The standard lore, i.e., that General Relativity effects suppress eccentricity, is only consistent with the parts of phase space where the General Relativity timescales are several orders of magnitude shorter than the secular Newtonian one. In other parts of phase space, however, post-Newtonian corrections combined with the three body ones, can excite eccentricities. In particular, for systems where the General Relativity timescale is comparable to the secular Newtonian timescales, the three-body interactions give rise to a resonant-like eccentricity excitation. Furthermore, for triples with a comparable-mass inner binary, where the eccentric Kozai-Lidov mechanism is suppressed, post-Newtonian corrections can further increase the eccentricity and lead to orbital flips even when the timescale of the former is much longer than the timescale of the secular Kozai-Lidov quadrupole perturbations.

#### Jun 21, 2012

1206.4316 (/preprints)
2012-06-21, 09:42 

## [1206.1330] Gravitational wave background from rotating neutron stars

Date: 6 Jun 2012

Abstract: The background of gravitational waves produced by the ensemble of rotating neutron stars (which includes pulsars, magnetars and gravitars) is investigated. A formula for \Omega(f) (commonly used to quantify the background) is derived, properly taking into account the time evolution of the systems since their formation until the present day. Moreover, the formula allows one to distinguish the different parts of the background: the unresolvable (which forms a stochastic background) and the resolvable. Several estimations of the background are obtained, for different assumptions on the parameters that characterize neutron stars and their population. In particular, different initial spin period distributions lead to very different results. For one of the models, with slow initial spins, the detection of the background can be rejected. However, other models do predict the detection of the background by the future ground-based gravitational wave detector ET. A robust upper limit for the background of rotating neutron stars is obtained; it does not exceed the detection threshold of two cross-correlated Advanced LIGO interferometers. If gravitars exist and constitute more than a few percent of the neutron star population, then they produce an unresolvable background that could be detected by ET. Under the most reasonable assumptions on the parameters characterizing a neutron star, the background is too faint. Previous papers have suggested neutron star models in which large magnetic fields (like the ones that characterize magnetars) induce big deformations in the star, which produce a stronger emission of gravitational radiation. Considering the most optimistic (in terms of the detection of gravitational waves) of these models, an upper limit for the background produced by magnetars is obtained; it could be detected by ET, but not by BBO or DECIGO.

#### Jun 20, 2012

1206.1330 (/preprints)
2012-06-20, 12:20 

## [1206.2509] Modeling a circular equatorial test-particle in a Kerr spacetime

Authors: J&#xe9;r&#xf4;me Carr&#xe9;, Edward K. Porter

Date: 12 Jun 2012

Abstract: Extreme Mass Ratio Inspirals (EMRIs) are one of the main gravitational wave (GW) sources for a future space detector, such as eLISA/NGO, and third generation ground-based detectors, like the Einstein Telescope. These systems present an interest both in astrophysics and fundamental physics. In order to make a high precision determination of their physical parameters, we need very accurate theoretical waveform models or templates. In the case of a circular equatorial orbit, the key stumbling block to the creation of these templates is the flux function of the GW. This function can be modeled either via very expensive numerical simulations, which then make the templates unusable for GW astronomy, or via some analytic approximation method such as a post-Newtonian approximation. This approximation is known to be asymptotically divergent and is only known up to 5.5PN order for the Schwarzschild case and to 4PN order for the Kerr case. A way to improve the convergence of the flux is to use re-summation methods. In this work we extend previous results using the Padé and Chebyshev approximations, first by taking into account the absorption of the GWs by the central black hole which was neglected in previous studies, and secondly by using the information from the Schwarzschild and absorption terms to create a Kerr flux up to 5.5PN order. We found that these two additions both improve the convergence. We also demonstrate that the best re-summation method for improving the flux model is based on a flux function which we call the "inverted Chebyshev approximation".

#### Jun 20, 2012

1206.2509 (/preprints)
2012-06-20, 12:19 

## [1206.2397] Survey of analogue spacetimes

Authors: Matt Visser (Victoria University of Wellington)

Date: 11 Jun 2012

Abstract: Analogue spacetimes, (and more boldly, analogue models both of and for gravity), have attracted significant and increasing attention over the last decade and a half. Perhaps the most straightforward physical example, which serves as a template for most of the others, is Bill Unruh's model for a dumb hole, (mute black hole, acoustic black hole), wherein sound is dragged along by a moving fluid — and can even be trapped behind an acoustic horizon. This and related analogue models for curved spacetimes are useful in many ways: Analogue spacetimes provide general relativists with extremely concrete physical models to help focus their thinking, and conversely the techniques of curved spacetime can sometimes help improve our understanding of condensed matter and/or optical systems by providing an unexpected and countervailing viewpoint. In this introductory chapter, I shall provide a few simple examples of analogue spacetimes as general background for the rest of the contributions.

#### Jun 20, 2012

1206.2397 (/preprints)
2012-06-20, 12:18 

## [1206.3461] Avoiding selection bias : A unified treatment of thresholded data

Authors: C. Messenger, J. Veitch

Date: 15 Jun 2012

Abstract: When searching for populations of rare and/or weak signals in noisy data, it is common to use a detection threshold to remove marginal events which are unlikely to be the signals of interest; or a detector might have limited sensitivity, causing it to not detect some of the population. In both cases a selection of data has occurred, which can potentially bias any inferences drawn from the remaining data, and this effect must be corrected for. We show how the selection bias is naturally avoided by using the full information from the search, considering both the selected data and our ignorance of the data that are thrown away, and considering all relevant signal and noise models. This approach produces unbiased estimates of parameters even in the presence of false alarms and incomplete data.

#### Jun 20, 2012

1206.3461 (/preprints)
2012-06-20, 12:18 

## [1206.2943] Do waveforms from binary black hole simulations depend on current choices of initial data?

Authors: Bryant Garcia, Geoffrey Lovelace, Lawrence E. Kidder, Michael Boyle, Saul A. Teukolsky, Mark A. Scheel, Bela Szilagyi

Date: 13 Jun 2012

Abstract: Initial data for numerical evolutions of binary-black holes have been dominated by conformally flat (CF) data because it is easy to construct. However, CF initial data cannot simulate nearly extremal spins while more complicated conformally curved initial data which is the superposition of two Kerr-Schild (SKS) black holes can. Here we establish the consistency between these two initial data schemes. We evolve the inspiral, merger, and ringdown of two equal-mass, nonspinning black holes using SKS initial data and compare with an analogous simulation using CF initial data. We find that the resultant gravitational-waveform phases agree to within $\delta \phi \laq 10ˆ{-2}$ radians and the amplitudes agree to within $\delta A/A \laq 5 \times 10ˆ{-3}$, which are within the numerical errors of the simulations. Furthermore, we find that the final mass and spin of the remnant black hole agree to one part in $10ˆ{-5}$.

#### Jun 20, 2012

1206.2943 (/preprints)
2012-06-20, 12:18 

## [1206.3015] Simulations of non-equal mass black hole binaries with spectral methods

Authors: Luisa T. Buchman, Harald P. Pfeiffer, Mark A. Scheel, Bela Szilagyi

Date: 14 Jun 2012

Abstract: This paper presents techniques and results for simulations of unequal mass, non-spinning black hole binaries with pseudo-spectral methods. Specifically, we develop an efficient root-finding procedure to ensure the black hole initial data have the desired masses and spins, we extend the dual coordinate frame method and eccentricity removal to asymmetric binaries. Furthermore, we describe techniques to simulate mergers of unequal mass black holes. The second part of the paper presents numerical simulations of non-spinning black hole binaries with mass ratios 2, 3, 4 and 6, covering between 15 and 22 orbits, merger and ringdown. We discuss the accuracy of these simulations, the evolution of the (initially zero) black hole spins, and the remnant black hole properties.

#### Jun 20, 2012

1206.3015 (/preprints)
2012-06-20, 12:17 

## [1206.3077] Can strong gravitational lensing distinguish naked singularities from black holes?

Authors: Satyabrata Sahu, Mandar Patil, D. Narasimha, Pankaj S. Joshi

Date: 14 Jun 2012

Abstract: In this paper we study gravitational lensing in the strong field limit from the perspective of cosmic censorship, to investigate whether or not naked singularities, if at all they exist in nature, can be distinguished from black holes. We study the gravitational lensing in the strong field regime in the JMN spacetime, a spherically symmetric geometry that contains a naked singularity and which matches smoothly with Schwarzschild metric beyond a finite radius. This metric is a toy model which was shown recently to be the end state of gravitational collapse. In the presence of the photon sphere gravitational lensing signature of this spacetime is identical to that of Schwarzschild black hole with infinitely many relativistic images and Einstein rings, all of them located beyond a certain critical angle from optic axis and the inner relativistic images all clumped together. However, in the absence of the photon sphere, which is the case for a wide range of parameter values in this spacetime, we show that we get finitely many relativistic images and Einstein rings spaced reasonably apart from one another, some of which can be formed inside the critical angle for the corresponding Schwarzschild black hole. This study suggests that the observation of relativistic images and rings might, in principle, allow us to unravel the existence of the naked singularity in the absence of the photon sphere. The results obtained here are in contrast with the earlier investigation on JNW naked singularities where relativistic images and rings were always absent in the absence of the photon sphere. We also point out the practical difficulties that might be encountered in the observation of the relativistic images and suggest that new dedicated experiments and techniques must be developed in future for this purpose.

#### Jun 20, 2012

1206.3077 (/preprints)
2012-06-20, 12:17 

## [1206.3803] On the mass radiated by coalescing black-hole binaries

Authors: Enrico Barausse, Viktoriya Morozova, Luciano Rezzolla

Date: 17 Jun 2012

Abstract: We derive a phenomenological expression that predicts the final mass of the black-hole remnant resulting from the merger of a generic binary system of black holes on quasi-circular orbits. Besides recovering the correct test-particle limit for extreme mass-ratio binaries, our formula reproduces well the results of all the numerical-relativity simulations published so far, both when applied at separations of a few gravitational radii, and when applied at separations of tens of thousands of gravitational radii. These validations make our formula a useful tool in a variety of contexts ranging from gravitational-wave physics to cosmology. As representative examples, we first illustrate how it can be used to decrease the phase error of the effective-one-body waveforms during the ringdown phase. Secondly, we show that, when combined with the recently computed self-force correction to the binding energy of nonspinning black-hole binaries, it provides an estimate of the energy emitted during the merger and ringdown. Finally, we use it to calculate the energy radiated in gravitational waves by massive black-hole binaries as a function of redshift, using different models for the seeds of the black-hole population.

#### Jun 20, 2012

1206.3803 (/preprints)
2012-06-20, 12:16 

## [1206.0703] GRB beaming and gravitational-wave observations

Authors: Hsin-Yu Chen, Daniel E. Holz

Date: 4 Jun 2012

Abstract: Using the observed rate of short-duration gamma-ray bursts (GRBs) it is possible to make predictions for the detectable rate of compact binary coalescences in gravitational-wave detectors. These estimates rely crucially on the growing consensus that short gamma-ray bursts are associated with the merger of two neutron stars or a neutron star and a black hole, but otherwise make no assumptions beyond the observed rate of short GRBs. In particular, our results do not assume coincident gravitational wave and electromagnetic observations. We show that the non-detection of mergers in the existing LIGO/Virgo data constrains the progenitor masses and beaming angles of gamma-ray bursts. For future detectors, we find that the first detection of a NS-NS binary coalescence associated with the progenitors of short GRBs is likely to happen within the first 16 months of observation, even in the case of a modest network of observatories (e.g., only LIGO-Hanford and LIGO-Livingston) operating at modest sensitivities (e.g., advanced LIGO design sensitivity, but without signal recycling mirrors), and assuming a conservative distribution of beaming angles (e.g. all GRBs beamed at \theta=30 deg). Less conservative assumptions reduce the waiting time until first detection to weeks to months. Alternatively, the compact binary coalescence model of short GRBs can be ruled out if a binary is not seen within the first two years of operation of a LIGO-Hanford, LIGO-Livingston, and Virgo network at advanced design sensitivity. We also demonstrate that the rate of GRB triggered sources is less than the rate of untriggered events if \theta<30 deg, independent of the noise curve, network configuration, and observed GRB rate. Thus the first detection in GWs of a binary GRB progenitor is unlikely to be associated with a GRB.

#### Jun 07, 2012

1206.0703 (/preprints)
2012-06-07, 01:18 

## [1206.0660] The non-integrability of the Zipoy-Voorhees metric

Authors: Georgios Lukes-Gerakopoulos

Date: 4 Jun 2012

Abstract: The low frequency gravitational wave detectors like eLISA/NGO will give us the opportunity to test whether the supermassive compact objects lying at the centers of galaxies are indeed Kerr black holes. A way to do such a test is to compare the gravitational wave signals with templates of perturbed black hole spacetimes, the so-called bumpy black hole spacetimes. The Zipoy-Voorhees (ZV) spacetime (known also as the $\gamma$ spacetime) can be included in the bumpy black hole family, because it can be considered as a perturbation of the Schwarzschild spacetime background. Several authors have suggested that the ZV metric corresponds to an integrable system. Contrary to this integrability conjecture, in the present article it is shown by numerical examples that in general ZV belongs to the family of non-integrable systems.

#### Jun 07, 2012

1206.0660 (/preprints)
2012-06-07, 01:17 

## [1206.0322] Testing Chern-Simons modified gravity with observations of extreme-mass-ratio binaries

Authors: Priscilla Canizares (1,2), Jonathan R. Gair (1), Carlos F. Sopuerta (2) ((1) IoA, Cambridge, (2) ICE, CSIC-IEEC)

Date: 1 Jun 2012

Abstract: Extreme-Mass-Ratio Inspirals (EMRIs) are one of the most promising sources of gravitational waves (GWs) for space-based detectors like the Laser Interferometer Space Antenna (LISA). EMRIs consist of a compact stellar object orbiting around a massive black hole (MBH). Since EMRI signals are expected to be long lasting (containing of the order of hundred thousand cycles), they will encode the structure of the MBH gravitational potential in a precise way such that features depending on the theory of gravity governing the system may be distinguished. That is, EMRI signals may be used to test gravity and the geometry of black holes. However, the development of a practical methodology for computing the generation and propagation of GWs from EMRIs in theories of gravity different than General Relativity (GR) has only recently begun. In this paper, we present a parameter estimation study of EMRIs in a particular modification of GR, which is described by a four-dimensional Chern-Simons (CS) gravitational term. We focus on determining to what extent a space-based GW observatory like LISA could distinguish between GR and CS gravity through the detection of GWs from EMRIs.

#### Jun 07, 2012

1206.0322 (/preprints)
2012-06-07, 01:16 

## [1206.0331] Scientific Objectives of Einstein Telescope

Authors: B. Sathyaprakash, M. Abernathy, F. Acernese, P. Ajith, B. Allen, P. Amaro-Seoane, N. Andersson, S. Aoudia, K. Arun, P. Astone, B. Krishnan, L. Barack, F. Barone, B. Barr, M. Barsuglia, M. Bassan, R. Bassiri, M. Beker, N. Beveridge, M. Bizouard, C. Bond, S. Bose, L. Bosi, S. Braccini, C. Bradaschia, M. Britzger, F. Brueckner, T. Bulik, H. J. Bulten, O. Burmeister, E. Calloni, P. Campsie, L. Carbone, G. Cella, E. Chalkley, E. Chassande-Mottin, S. Chelkowski, A. Chincarini, A. Di. Cintio, J. Clark, E. Coccia, C. N. Colacino, J. Colas, A. Colla, A. Corsi, A. Cumming, L. Cunningham, E. Cuoco, S. Danilishin, K. Danzmann, E. Daw, R. De. Salvo, W. Del. Pozzo, T. Dent, R. De. Rosa, L. Di. Fiore, M. Di. Paolo. Emilio, A. Di. Virgilio, A. Dietz, M. Doets, J. Dueck, M. Edwards, V. Fafone, S. Fairhurst, P. Falferi, M. Favata, V. Ferrari, F. Ferrini, F. Fidecaro, R. Flaminio, J. Franc, F. Frasconi, A. Freise, D. Friedrich, P. Fulda, J. Gair, M. Galimberti, G. Gemme, E. Genin, A. Gennai, A. Giazotto, K. Glampedakis, S. Gossan, R. Gouaty, C. Graef, W. Graham, M. Granata, H. Grote, G. Guidi, J. Hallam, G. Hammond, M. Hannam, J. Harms, K. Haughian, I. Hawke, D. Heinert, M. Hendry, I. Heng, E. Hennes, S. Hild, J. Hough, D. Huet, S. Husa, S. Huttner, B. Iyer, D. I. Jones, G. Jones, I. Kamaretsos, C. Kant Mishra, F. Kawazoe, F. Khalili, B. Kley, K. Kokeyama, K. Kokkotas, S. Kroker, R. Kumar, K. Kuroda, B. Lagrange, N. Lastzka, T. G. F. Li, M. Lorenzini, G. Losurdo, H. L&#xfc;ck, E. Majorana, V. Malvezzi, I. Mandel, V. Mandic, S. Marka, F. Marin, F. Marion, J. Marque, I. Martin, D. Mc. Leod, D. Mckechan, M. Mehmet, C. Michel, Y. Minenkov, N. Morgado, A. Morgia, S. Mosca, L. Moscatelli, B. Mours, H. M&#xfc;ller-Ebhardt, P. Murray, L. Naticchioni, R. Nawrodt, J. Nelson, R. O&#x27;. Shaughnessy, C. D. Ott, C. Palomba, A. Paoli, G. Parguez, A. Pasqualetti, R. Passaquieti, D. Passuello, M. Perciballi, F. Piergiovanni, L. Pinard, M. Pitkin, W. Plastino, M. Plissi, R. Poggiani, P. Popolizio, E. Porter, M. Prato, G. Prodi, M. Punturo, P. Puppo, D. Rabeling, I. Racz, P. Rapagnani, V. Re, J. Read, T. Regimbau, H. Rehbein, S. Reid, F. Ricci, F. Richard, C. Robinson, A. Rocchi, R. Romano, S. Rowan, A. R&#xfc;diger, A. Samblowski, L. Santamar&#xed;a, B. Sassolas, R. Schilling, P. Schmidt, R. Schnabel, B. Schutz, C. Schwarz, J. Scott, P. Seidel, A. M. Sintes, K. Somiya, C. F. Sopuerta, B. Sorazu, F. Speirits, L. Storchi, K. Strain, S. Strigin, P. Sutton, S. Tarabrin, B. Taylor, A. Th&#xfc;rin, K. Tokmakov, M. Tonelli, H. Tournefier, R. Vaccarone, H. Vahlbruch, J. F. J. van. den. Brand, C. Van. Den. Broeck, S. van. der. Putten, M. van. Veggel, A. Vecchio, J. Veitch, F. Vetrano, A. Vicere, S. Vyatchanin, P. We&#xdf;els, B. Willke, W. Winkler, G. Woan, A. Woodcraft, K. Yamamoto

Date: 2 Jun 2012

Abstract: The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.

#### Jun 07, 2012

1206.0331 (/preprints)
2012-06-07, 01:16 

## [1206.0915] Search for the PN coefficients for the Energy flux through Gravitational Waves from Black-Hole Binaries using Markov Chain Monte Carlo

Authors: Prayush Kumar

Date: 5 Jun 2012

Abstract: In this work, the focus is on the improvement of the existing post-Newtonian approximation for the gravitational flux from Super Massive Black Hole Binaries. In order to improve the existing templates for LISA, we need more accurate post-Newtonian expansions for the gravitational flux. Stochastic search techniques like the Markov Chain Monte Carlo (MCMC) have been used extensively for searching for sky parameters etc. The idea is to combine the two and approach the problem of finding post-Newtonian coefficients using MCMC. It has been shown that matching against a 5.5PN signal, with noise, the last coefficient can be found by MCMC very easily and displays fast convergence. Also the space for higher dimensional searches are explored.

#### Jun 07, 2012

1206.0915 (/preprints)
2012-06-07, 01:14 

## [1206.0744] On the point mass approximation to calculate the gravitational wave signal from white dwarf binaries

Authors: D. van den Broek, G. Nelemans, M. Dan, S. Rosswog

Date: 4 Jun 2012

Abstract: Double white dwarf binaries in the Galaxy dominate the gravitational wave sky and would be detectable for an instrument such as LISA. Most studies have calculated the expected gravitational wave signal under the assumption that the binary white dwarf system can be represented by two point masses in orbit. We discuss the accuracy of this approximation for real astrophysical systems. For non-relativistic binaries in circular orbit the gravitational wave signal can easily be calculated. We show that for these systems the point mass approximation is completely justified when the individual stars are axisymmetric irrespective of their size. We find that the signal obtained from Smoothed-Particle Hydrodynamics simulations of tidally deformed, Roche-lobe filling white dwarfs, including one case when an accretion disc is present, is consistent with the point mass approximation. The difference is typically at the level of one per cent or less in realistic cases, yielding small errors in the inferred parameters of the binaries.

#### Jun 07, 2012

1206.0744 (/preprints)
2012-06-07, 01:12 

## [1206.0818] A New Method for Gravitational Wave Detection with Atomic Sensors

Authors: Peter W. Graham, Jason M. Hogan, Mark A. Kasevich, Surjeet Rajendran

Date: 5 Jun 2012

Abstract: Laser frequency noise is a dominant noise background for the detection of gravitational waves using long-baseline optical interferometry. Amelioration of this noise requires near simultaneous strain measurements on more than one interferometer baseline, necessitating, for example, more than two satellites for a space-based detector, or two interferometer arms for a ground-based detector. We describe a new detection strategy based on recent advances in optical atomic clocks and atom interferometry which can operate at long-baselines and which is immune to laser frequency noise. Laser frequency noise is suppressed because the signal arises strictly from the light propagation time between two ensembles of atoms. This new class of sensor allows sensitive gravitational wave detection with only a single baseline. This approach also has practical applications in, for example, the development of ultra-sensitive gravimeters and gravity gradiometers.

#### Jun 07, 2012

1206.0818 (/preprints)
2012-06-07, 01:12 

## [1206.1225] Cosmology and fundamental physics with the Euclid satellite

Authors: Luca Amendola, Stephen Appleby, David Bacon, Tessa Baker, Marco Baldi, Nicola Bartolo, Alain Blanchard, Camille Bonvin, Stefano Borgani, Enzo Branchini, Clare Burrage, Stefano Camera, Carmelita Carbone, Luciano Casarini, Mark Cropper, Claudia deRham, Cinzia di Porto, Anne Ealet, Pedro G. Ferreira, Fabio Finelli, Juan Garcia-Bellido, Tommaso Giannantonio, Luigi Guzzo, Alan Heavens, Lavinia Heisenberg, Catherine Heymans, Henk Hoekstra, Lukas Hollenstein, Rory Holmes, Ole Horst, Knud Jahnke, Thomas D. Kitching, Tomi Koivisto, Martin Kunz, Giuseppe La Vacca, Marisa March, Elisabetta Majerotto, Katarina Markovic, David Marsh, Federico Marulli, Richard Massey, Yannick Mellier, David F. Mota, Nelson Nunes, Will Percival, Valeria Pettorino, Cristiano Porciani, Claudia Quercellini, Justin Read, Massimiliano Rinaldi, Domenico Sapone, Roberto Scaramella, Constantinos Skordis, Fergus Simpson, Andy Taylor, Shaun Thomas, Roberto Trotta, Licia Verde, Filippo Vernizzi, Adrian Vollmer, Yun Wang, Jochen Weller, Tom Zlosnik

Date: 6 Jun 2012

Abstract: Euclid is a European Space Agency medium class mission selected for launch in 2019 within the Cosmic Vision 2015-2025 programme. The main goal of Euclid is to understand the origin of the accelerated expansion of the Universe. Euclid will explore the expansion history of the Universe and the evolution of cosmic structures by measuring shapes and redshifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid's Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.

#### Jun 07, 2012

1206.1225 (/preprints)
2012-06-07, 01:11 

## [1206.1109] Caustic echoes from a Schwarzschild black hole

Authors: An\il Zengino&#x11f;lu, Chad R. Galley

Date: 6 Jun 2012

Abstract: We present the first numerical construction of the scalar Schwarzschild Green function in the time-domain, which reveals several universal features of wave propagation in black hole spacetimes. We demonstrate the trapping of energy near the photon sphere and confirm its exponential decay. The trapped wavefront propagates through caustics resulting in echoes that propagate to infinity. The arrival times and the decay rate of these caustic echoes are consistent with propagation along null geodesics and the large l-limit of quasinormal modes. We show that the four-fold singularity structure of the retarded Green function is due to the well-known action of a Hilbert transform on the trapped wavefront at caustics. A two-fold cycle is obtained for degenerate source-observer configurations along the caustic line, where the energy amplification increases with an inverse power of the scale of the source. Finally, we discuss the tail piece of the solution due to propagation within the light cone, up to and including null infinity, and argue that, even with ideal instruments, only a finite number of echoes can be observed. Putting these pieces together, we provide a heuristic expression that approximates the Green function with a few free parameters. Accurate calculations and approximations of the Green function are the most general way of solving for wave propagation in curved spacetimes and should be useful in a variety of studies such as the computation of the self-force on a particle.

#### Jun 07, 2012

1206.1109 (/preprints)
2012-06-07, 01:11 

## [1206.1056] White Dwarf Kinematics vs Mass

Authors: Christopher Wegg, E. Sterl Phinney

Date: 5 Jun 2012

Abstract: We have investigated the relationship between the kinematics and mass of young (<3x10ˆ8 years) white dwarfs using proper motions. Our sample is taken from the colour selected catalogues of SDSS (Eisenstein et al. 2006) and the Palomar-Green Survey (Liebert, Bergeron & Holberg 2005), both of which have spectroscopic temperature and gravity determinations. We find that the dispersion decreases with increasing white dwarf mass. This can be explained as a result of less scattering by objects in the Galactic disk during the shorter lifetime of their more massive progenitors. A direct result of this is that white dwarfs with high mass have a reduced scale height, and hence their local density is enhanced over their less massive counterparts. In addition, we have investigated whether the kinematics of the highest mass white dwarfs (>0.95Msun) are consistent with the expected relative contributions of single star evolution and mergers. We find that the kinematics are consistent with the majority of high-mass white dwarfs being formed through single star evolution.

#### Jun 07, 2012

1206.1056 (/preprints)
2012-06-07, 01:09 

## [1206.0028] Design and characteristics of a WEP test in a sounding-rocket payload

Authors: Robert D. Reasenberg, Biju R. Patla, James D. Phillips, Rajesh Thapa

Date: 31 May 2012

Abstract: We describe SR-POEM, a Galilean test of the weak equivalence principle that is to be conducted during the free fall portion of the flight of a sounding rocket payload. This test of a single pair of substances will have a measurement uncertainty of {\sigma}({\eta}) < 2 10ˆ17 after averaging the results of eight separate drops, each of 120 s duration. The entire payload is inverted between successive drops to cancel potential sources of systematic error. The weak equivalence principle measurement is made with a set of four of the SAO laser gauges, which have achieved an Allan deviation of 0.04 pm for an averaging time of 30 s. We discuss aspects of the current design with an emphasis on those that bear on the accuracy of the determination of {\eta}. The discovery of a violation ({\eta} \neq 0) would have profound implications for physics, astrophysics and cosmology.

#### Jun 04, 2012

1206.0028 (/preprints)
2012-06-04, 02:11 

## [1205.5268] The gap closes: a new scenario for the evolution of supermassive black hole binaries with gaseous disks

Authors: Bence Kocsis, Zoltan Haiman, Abraham Loeb

Date: 23 May 2012

Abstract: We study the interaction of a supermassive black hole (SMBH) binary and a standard radiatively efficient thin accretion disk. We examine steady-state configurations of the disk and migrating SMBH system, self-consistently accounting for tidal and viscous torques and heating, radiative diffusion limited cooling, gas and radiation pressure, and the decay of the binary's orbit. We obtain a "phase diagram" of the system as a function of binary parameters, showing regimes in which both the disk structure and migration have a different character. Although massive binaries can create a central gap in the disk at large radii, the tidal barrier of the secondary causes a significant pile-up of gas outside of its orbit, which can lead to the closing of the gap. We find that this spillover occurs at an orbital separation as large as ~200 M_7ˆ{-½} gravitational radii, where M = 10ˆ7 M_7 Msun is the total binary mass. If the secondary is less massive than ~10ˆ6 Msun, then the gap is closed before gravitational waves (GWs) start dominating the orbital decay. In this regime, the disk is still strongly perturbed, but the piled-up gas continuously overflows as in a porous dam, and crosses inside the secondary's orbit. The corresponding migration rate, which we label Type 1.5, is slower than the usual limiting cases known as Type I and II migration. Compared to an unperturbed disk, the steady-state disk in the overflowing regime is up to several hundred times brighter in the optical bands. Surveys such as PanSTARRS or LSST may discover the periodic variability of this population of binaries. Our results imply that the circumbinary disks around SMBHs can extend to small radii during the last stages of their merger, when they are detectable by LISA, and may produce coincident electromagnetic (EM) emission similar to active galactic nuclei (AGN).

#### Jun 01, 2012

1205.5268 (/preprints)
2012-06-01, 18:05 

## [1205.5562] Accurate modeling of intermediate-mass-ratio inspirals: exploring the form of the self-force in the intermediate-mass-ratio regime

Authors: E. A. Huerta, Prayush Kumar, Duncan A. Brown

Date: 24 May 2012

Abstract: The LIGO detector is undergoing a major upgrade that will increase its sensitivity by a factor of 10, and extend its bandwidth from 40 Hz to 10 Hz on the lower frequency end, while also allowing for high-frequency operation due to its tunability. This advanced LIGO (aLIGO) detector will extend the mass range at which compact mass binaries may be detected by a factor of four or more at a fixed signal-to-noise ratio [1]. The inspirals of stellar-mass compact objects into intermediate-mass black holes (IMBHs) of 50-350 solar masses will lie in the frequency band of aLIGO [2]. GW searches for these type of events will provide conclusive evidence for the existence of IMBHs and explore the dynamics of cluster environments. To realize this science we need to develop waveform templates that accurately capture the dynamical evolution of these type of events before aLIGO begins observations. Implementing gravitational self-force (SF) corrections in templates for compact binaries with mass-ratios 1:10-1:1000 will be essential to decode the information contained in the GW signals emitted by these sources. However, these SF corrections have been computed for low-frequency events with extreme mass-ratios 1:10ˆ4-1:10ˆ7. We develop a waveform model that accurately reproduces the dynamical evolution of intermediate mass ratio inspirals, as predicted by the effective-one-body (EOB) model introduced in [3], and which enables us to shed some light on the form of the SF for events with mass-ratio 1:6, 1:10 and 1:100. To complement this study, we make use of SF results in the extreme-mass-ratio regime, and of predictions of the EOB model introduced in [3], to derive a prescription for the shift of the orbital frequency at the innermost stable circular orbit which consistently captures predictions from the extreme, intermediate and comparable mass-ratio regimes.

#### Jun 01, 2012

1205.5562 (/preprints)
2012-06-01, 18:04 

## [1205.6009] Towards beating the curse of dimensionality for gravitational waves using Reduced Basis

Authors: Frank Herrmann, Scott E. Field, Chad R. Galley, Evan Ochsner, Manuel Tiglio

Date: 27 May 2012

Abstract: Using the Reduced Basis approach, we efficiently compress and accurately represent the space of waveforms for non-precessing binary black hole inspirals, which constitutes a four dimensional parameter space (two masses, two spin magnitudes). Compared to the non-spinning case, we find that only a {\it marginal} increase in the (already relatively small) number of reduced basis elements is required to represent any non-precessing waveform to nearly numerical round-off precision. Most parameters selected by the algorithm are near the boundary of the parameter space, leaving the bulk of its volume sparse. Our results suggest that the full eight dimensional space (two masses, two spin magnitudes, four spin orientation angles on the unit sphere) may be highly compressible and represented with very high accuracy by a remarkably small number of waveforms, thus providing some hope that the number of numerical relativity simulations of binary black hole coalescences needed to represent the entire space of configurations is not intractable. Finally, we find that the {\it distribution} of selected parameters is robust to different choices of seed values starting the algorithm, a property which should be useful for indicating parameters for numerical relativity simulations of binary black holes. In particular, we find that the mass ratios $m_1/m_2$ of non-spinning binaries selected by the algorithm are mostly in the interval $[1,3]$ and that the median of the distribution follows a power-law behavior $\sim (m_1/m_2)ˆ{-5.25}$.

#### Jun 01, 2012

1205.6009 (/preprints)
2012-06-01, 18:03 

## [1205.6215] Probing deviations from General Relativity with the Euclid spectroscopic survey

Authors: Elisabetta Majerotto, Luigi Guzzo, Lado Samushia, Will J. Percival, Yun Wang, Sylvain de la Torre, Bianca Garilli, Paolo Franzetti, Emanuel Rossetti, Andrea Cimatti, Carmelita Carbone, Nathan Roche, Giovanni Zamorani

Date: 28 May 2012

Abstract: We discuss the ability of the planned Euclid mission to detect deviations from General Relativity using its extensive redshift survey of more than 50 Million galaxies. Constraints on the gravity theory are placed measuring the growth rate of structure within 14 redshift bins between z=0.7 and z=2. The growth rate is measured from redshift-space distortions, i.e. the anisotropy of the clustering pattern induced by coherent peculiar motions. This is performed in the overall context of the Euclid spectroscopic survey, which will simultaneously measure the expansion history of the universe, using the power spectrum and its baryonic features as a standard ruler, accounting for the relative degeneracies of expansion and growth parameters. The resulting expected errors on the growth rate in the different redshift bins, expressed through the quantity f\sigma_8, range between 1.3% and 4.4%. We discuss the optimisation of the survey configuration and investigate the important dependence on the growth parameterisation and the assumed cosmological model. We show how a specific parameterisation could actually drive the design towards artificially restricted regions of the parameter space. Finally, in the framework of the popular "\gamma -parameterisation", we show that the Euclid spectroscopic survey alone will already be able to provide substantial evidence (in Bayesian terms) if the growth index differs from the GR value \gamma=0.55 by at least \sim 0.13. This will combine with the comparable inference power provided by the Euclid weak lensing survey, resulting in Euclid's unique ability to provide a decisive test of modified gravity.

#### Jun 01, 2012

1205.6215 (/preprints)
2012-06-01, 18:03 

## [1205.7063] Tests of General Relativity in the Strong Gravity Regime Based on X-Ray Spectropolarimetric Observations of Black Holes in X-Ray Binaries

Authors: Henric Krawczynski (Washington University in St. Louis)

Date: 31 May 2012

Abstract: Although General Relativity (GR) has been tested extensively in the weak gravity regime, similar tests in the strong gravity regime are still missing. In this paper we explore the possibility to use X-ray spectropolarimetric observations of black holes in X-ray binaries to distinguish between the Kerr metric and the phenomenological metrics introduced by Johannsen and Psaltis (2011) (which are not vacuum solutions of Einstein's equation) and thus to test the no-hair theorem of GR. To this end, we have developed a numerical code that calculates the radial brightness profiles of accretion disks and parallel transports the wave vector and polarization vector of photons through the Kerr and non-GR spacetimes. We used the code to predict the observational appearance of GR and non-GR accreting black hole systems. We find that the predicted energy spectra and energy dependent polarization degree and polarization direction do depend strongly on the underlying spacetime. However, for large regions of the parameter space, the GR and non-GR metrics lead to very similar observational signatures, making it difficult to observationally distinguish between the two types of models.

#### Jun 01, 2012

1205.7063 (/preprints)
2012-06-01, 18:02 

## [1205.6592] Spectroscopy of the Schwarzschild Black Hole at Arbitrary Frequencies

Authors: Marc Casals, Adrian C. Ottewill

Date: 30 May 2012

Abstract: Linear field perturbations of a black hole are described by the Green function of the wave equation that they obey. After Fourier decomposing the Green function, its two natural contributions are given by poles (quasinormal modes) and a largely unexplored branch cut in the complex-frequency plane. We present new analytic methods for calculating the branch cut on a Schwarzschild black hole for {\it arbitrary} values of the frequency. The branch cut yields a power-law tail decay for late times in the response of a black hole to an initial perturbation. We determine explicitly the first three orders in the power-law and show that the branch cut also yields a new logarithmic behaviour for late times. Before the tail sets in, the quasinormal modes dominate the black hole response. For electromagnetic perturbations, the quasinormal mode frequencies approach the branch cut at large overtone index $n$. We determine these frequencies up to $nˆ{-5/2}$ and, formally, to {\it arbitrary} order. Highly-damped quasinormal modes are also of interest in that they have been linked to quantum properties of black holes.

#### Jun 01, 2012

1205.6592 (/preprints)
2012-06-01, 18:02 

## [1205.6611] Improved source localization with LIGO India

Authors: Stephen Fairhurst

Date: 30 May 2012

Abstract: A global network of advanced gravitational wave interferometric detectors is under construction. These detectors will offer an order of magnitude improvement in sensitivity over the initial detectors and will usher in the era of gravitational wave astronomy. In this paper, we evaluate the benefits of relocating one of the advanced LIGO detectors to India.

#### Jun 01, 2012

1205.6611 (/preprints)
2012-06-01, 18:02 

## [1205.7006] On the validity of the adiabatic approximation in compact binary inspirals

Authors: A. Maselli, L. Gualtieri, F. Pannarale, V. Ferrari

Date: 31 May 2012

Abstract: Using a semi-analytical approach recently developed to model the tidal deformations of neutron stars in inspiralling compact binaries, we study the dynamical evolution of the tidal tensor, which we explicitly derive at second post-Newtonian order, and of the quadrupole tensor. Since we do not assume a priori that the quadrupole tensor is proportional to the tidal tensor, i.e. the so called "adiabatic approximation", our approach enables us to establish to which extent such approximation is reliable. We find that the ratio between the quadrupole and tidal tensors (i.e., the Love number) increases as the inspiral progresses, but this phenomenon only marginally affects the emitted gravitational waveform. We estimate the frequency range in which the tidal component of the gravitational signal is well described using the stationary phase approximation at next-to-leading post-Newtonian order, comparing different contributions to the tidal phase. We also derive a semi-analytical expression for the Love number, which reproduces within a few percentage points the results obtained so far by numerical integrations of the relativistic equations of stellar perturbations.

#### Jun 01, 2012

1205.7006 (/preprints)
2012-06-01, 18:01 

## [1205.3926] Influence of internal structure on the motion of test bodies in extreme mass ratio situations

Authors: Jan Steinhoff, Dirk Puetzfeld

Date: 17 May 2012

Abstract: We investigate the motion of test bodies with internal structure in General Relativity. With the help of a multipolar approximation method for extended test bodies we derive the equations of motion up to the quadrupolar order. The motion of pole-dipole and quadrupole test bodies is studied in the context of the Kerr geometry. For an explicit quadrupole model, which includes spin and tidal interactions, the motion in the equatorial plane is characterized by an effective potential and by the binding energy. We compare our findings to recent results for the conservative part of the self-force of bodies in extreme mass ratio situations. Possible implications for gravitational wave physics are outlined.

#### May 24, 2012

1205.3926 (/preprints)
2012-05-24, 14:26 

## [1205.4530] On the comparison of results regarding the post-Newtonian approximate treatment of the dynamics of extended spinning compact binaries

Authors: Steven Hergt, Jan Steinhoff, Gerhard Schaefer

Date: 21 May 2012

Abstract: A brief review is given of all the Hamiltonians and effective potentials calculated hitherto covering the post-Newtonian (pN) dynamics of a two body system. A method is presented to compare (conservative) reduced Hamiltonians with nonreduced potentials directly at least up to the next-to-leading-pN order.

#### May 24, 2012

1205.4530 (/preprints)
2012-05-24, 14:25 

## [1205.4620] Single-detector searches for a stochastic background of gravitational radiation

Authors: Massimo Tinto, J. W. Armstrong

Date: 21 May 2012

Abstract: We propose a data processing technique that allows searches for a stochastic background of gravitational radiation with data from a single detector. Our technique exploits the difference between the coherence time of the gravitational wave (GW) signal and that of the instrumental noise affecting the measurements. By estimating the auto-correlation function of the data at an off-set time that is longer than the coherence time of the noise {\underbar {but}} shorter than the coherence time of the GW signal, we can effectively enhance the power signal-to-noise ratio (SNR) by the square-root of the integration time. The resulting SNR is comparable in magnitude to that achievable by cross-correlating the data from two co-located and co-aligned detectors whose noises are uncorrelated. Our method is general and it can be applied to data from ground- and space-based detectors, as well as from pulsar timing experiments.

#### May 24, 2012

1205.4620 (/preprints)
2012-05-24, 14:25 

## [1205.4440] The representation of physical motions by various types of quaternions

Authors: D. H. Delphenich

Date: 20 May 2012

Abstract: It is shown that the groups of Euclidian rotations, rigid motions, proper, orthochronous Lorentz transformations, and the complex rigid motions can be represented by the groups of unit-norm elements in the algebras of real, dual, complex, and complex dual quaternions, respectively. It is shown how someof the physically-useful tensors and spinors can be represented by the various kinds of quaternions. The basic notions of kinematical states are described in each case, except complex dual quaternions, where their possible role in describing the symmetries of the Maxwell equations is discussed.

#### May 24, 2012

1205.4440 (/preprints)
2012-05-24, 14:24 

## [1205.4713] The role of the supermassive black hole spin in the estimation of the EMRI event rate

Authors: Pau Amaro-Seoane, Carlos F. Sopuerta, Marc Dewi Freitag

Date: 21 May 2012

Abstract: One of the main channels of interactions in galactic nuclei between stars and the central massive black hole (MBH) is the gradual inspiral of compact remnants into the MBH due to the emission of gravitational radiation. Previous works about the estimation of how many events space observatories such as LISA will be able to observe during its operational time differ in orders of magnitude, due to the complexity of the problem. Nevertheless, a common result to all investigations is that a plunge is much more likely than a slow adiabatic inspiral, an EMRI. The event rates for plunges are orders of magnitude larger than slow inspirals. On the other hand, nature MBH's are most likely Kerr and the magnitude of the spin has been sized up to be high. We calculate the number of periapsis passages that a compact object set on to an extremely radial orbit goes through before being actually swallowed by the Kerr MBH and we then translate it into an event rate for a LISA-like observatory. We prove that a "plunging" compact object is conceptually indistinguishable from an adiabatic, slow inspiral. This has an important impact on the event rate, enhancing in some cases significantly, depending on the spin of the MBH and the inclination: If the orbit of the EMRI is prograde, the effective size of the MBH becomes smaller the larger the spin is, whilst if retrograde, it becomes bigger. However, this situation is not symmetric, resulting in an effective enhancement of the rates. The effect of vectorial resonant relaxation on the sense of the orbit does not affect the enhancement. The strong dependence on the spin magnitude and orbital orientation of the EMRI on the rates will allow us to study stellar dynamics in a regime which is invisible to photon-based astrophysics.

#### May 24, 2012

1205.4713 (/preprints)
2012-05-24, 14:23 

## [1205.5017] Structure and evolution of circumbinary disks around supermassive black hole (SMBH) binaries

Authors: Roman R. Rafikov (Princeton)

Date: 22 May 2012

Abstract: It is generally believed that gaseous disks around supermassive black hole (SMBH) binaries in centers of galaxies can facilitate binary merger and give rise to observational signatures both in electromagnetic and gravitational wave domains. We explore general properties of circumbinary disks by reformulating standard equations for the viscous disk evolution in terms of the viscous angular momentum flux F_J. In steady state F_J is a linear function of the specific angular momentum, which is a generalization of (but is not equivalent to) the standard constant \dot M disk solution. If the torque produced by the central binary is effective at stopping gas inflow and opening a gap (or cavity) in the disk, then the inner part of the circumbinary disk can be approximated as a constant F_J disk. We compute properties of such disks in different physical regimes relevant for SMBH binaries and use these results to understand the gas-assisted evolution of SMBH pairs starting at separations 10ˆ{-4}-10ˆ{-2} pc. We find the following. (1) Pile-up of matter at the inner edge of the disk leads to continuous growth of the torque acting on the binary and can considerably accelerate its orbital evolution compared to the gravitational wave-driven decay. (2) Torque on the binary is determined non-locally and does not in general reflect the disk properties in the vicinity of the binary. (3) Binary evolution depends on the past history of the disk evolution. (4) Eddington limit can be important in circumbinary disks even if they accrete at sub-Eddington rates at late stages of binary evolution. (5) Circumbinary disk self-consistently evolved under the action of the binary torque emits more power and has spectrum different from the spectrum of constant \dot M disk - it is steeper (\nu F_\nu\propto \nuˆ{12/7}) and extends to shorter wavelength, facilitating its detection.

#### May 24, 2012

1205.5017 (/preprints)
2012-05-24, 14:22 

## [1205.5175] Orbit optimization for ASTROD-GW and its time delay interferometry with two arms using CGC ephemeris

Authors: G. Wang, W.-T. Ni

Date: 23 May 2012

Abstract: ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitation Wave detection) is an optimization of ASTROD to focus on the goal of detection of gravitation waves. The detection sensitivity is shifted 52 times toward larger wavelength compared to that of LISA. The mission orbits of the 3 spacecraft forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and L5. The 3 spacecraft range interferometrically with one another with arm length about 260 million kilometers. In order to attain the requisite sensitivity for ASTROD-GW, laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. For suppressing laser frequency noise, we need to use time delay interferometry (TDI) to match the two different optical paths (times of travel). Since planets and other solar-system bodies perturb the orbits of ASTROD-GW spacecraft and affect the (TDI), we simulate the time delay numerically using CGC 2.7 ephemeris framework. To conform to the ASTROD-GW planning, we work out a set of 20-year optimized mission orbits of ASTROD-GW spacecraft starting at June 21, 2028, and calculate the residual optical path differences in the first and second generation TDI for one-detector case. In our optimized mission orbits for 20 years, changes of arm length are less than 0.0003 AU; the relative Doppler velocities are less than 3m/s. All the second generation TDI for one-detector case satisfies the ASTROD-GW requirement.

#### May 24, 2012

1205.5175 (/preprints)
2012-05-24, 14:21 

## [1205.5240] Stellar dynamics and extreme-mass ratio inspirals

Authors: Pau Amaro-Seoane

Date: 23 May 2012

Abstract: Nowadays it is well-established that in the centre of the Milky Way a massive black hole (MBH) with a mass of about four million solar masses is lurking. While there is an emerging consensus about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses such as the one in our galactic centre remain an understudied enigma. The key to understanding these holes, how some of them grow by orders of magnitude in mass is to understand the dynamics of the stars in the galactic neighborhood. Stars and the central MBH chiefly interact through the gradual inspiral of the stars into the MBH due to the emission of gravitational radiation. Also stars produce gases which will be subsequently accreted by the MBH by collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which will could be surveyed by a millihertz gravitational wave interferometer scrutinizing the range of masses fundamental to the understanding of the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes "eat" stars that happen to be near them.

#### May 24, 2012

1205.5240 (/preprints)
2012-05-24, 14:21 

## [1205.4747] Principles of High-Dimensional Data Visualization in Astronomy

Authors: Alyssa A. Goodman

Date: 21 May 2012

Abstract: Astronomical researchers often think of analysis and visualization as separate tasks. In the case of high-dimensional data sets, though, interactive exploratory data visualization can give far more insight than an approach where data processing and statistical analysis are followed, rather than accompanied, by visualization. This paper attempts to charts a course toward "linked view" systems, where multiple views of high-dimensional data sets update live as a researcher selects, highlights, or otherwise manipulates, one of several open views. For example, imagine a researcher looking at a 3D volume visualization of simulated or observed data, and simultaneously viewing statistical displays of the data set's properties (such as an x-y plot of temperature vs. velocity, or a histogram of vorticities). Then, imagine that when the researcher selects an interesting group of points in any one of these displays, that the same points become a highlighted subset in all other open displays. Selections can be graphical or algorithmic, and they can be combined, and saved. For tabular (ASCII) data, this kind of analysis has long been possible, even though it has been under-used in Astronomy. The bigger issue for Astronomy and several other "high-dimensional" fields is the need systems that allow full integration of images and data cubes within a linked-view environment. The paper concludes its history and analysis of the present situation with suggestions that look toward cooperatively-developed open-source modular software as a way to create an evolving, flexible, high-dimensional, linked-view visualization environment useful in astrophysical research.

#### May 24, 2012

1205.4747 (/preprints)
2012-05-24, 14:21 

## [1205.4020] Secular Dynamical Anti-Friction in Galactic Nuclei

Date: 17 May 2012

Abstract: We identify a gravitational-dynamical process in near-Keplerian potentials of galactic nuclei that occurs when an intermediate-mass black hole (IMBH) is migrating on an eccentric orbit through the stellar cluster towards the central supermassive black hole (SMBH). We find that, apart from conventional dynamical friction, the IMBH experiences an often much stronger systematic torque due to the secular (i.e., orbit-averaged) interactions with the cluster's stars. The force which results in this torque is applied, counterintuitively, in the same direction as the IMBH's precession and we refer to its action as "secular-dynamical anti-friction" (SDAF). We argue that SDAF, and not the gravitational ejection of stars, is responsible for the IMBH's eccentricity increase seen in the initial stages of previous N-body simulations. Our numerical experiments, supported by qualitative arguments, demonstrate that (1) when the IMBH's precession direction is artificially reversed, the torque changes sign as well, which decreases the orbital eccentricity, (2) the rate of eccentricity growth is sensitive to the IMBH migration rate, with zero systematic eccentricity growth for an IMBH whose orbit is artificially prevented from inward migration, and (3) SDAF is the strongest when the central star cluster is rapidly rotating. This leads to eccentricity growth/decrease for the clusters rotating in the opposite/same direction relative to the IMBH's orbital motion.

#### May 21, 2012

1205.4020 (/preprints)
2012-05-21, 10:13 

## [1204.4218] Optimal strategies for continuous gravitational wave detection in pulsar timing arrays

Authors: Justin Ellis, Xavier Siemens, Jolien Creighton

Date: 18 Apr 2012

Abstract: Supermassive black hole binaries (SMBHBs) are expected to emit continuous gravitational waves in the pulsar timing array (PTA) frequency band ($10ˆ{-9}$--$10ˆ{-7}$ Hz). The development of data analysis techniques aimed at efficient detection and characterization of these signals is critical to the gravitational wave detection effort. In this paper we leverage methods developed for LIGO continuous wave gravitational searches, and explore the use of the $\mathcal{F}$-statistic for such searches in pulsar timing data. Babak & Sesana 2012 have already used this approach in the context of PTAs to show that one can resolve multiple SMBHB sources in the sky. Our work improves on several aspects of prior continuous wave search methods developed for PTA data analysis. The algorithm is implemented fully in the time domain, which naturally deals with the irregular sampling typical of PTA data and avoids spectral leakage problems associated with frequency domain methods. We take into account the fitting of the timing model, and have generalized our approach to deal with both correlated and uncorrelated colored noise sources. We also develop an incoherent detection statistic that maximizes over all pulsar dependent contributions to the likelihood. To test the effectiveness and sensitivity of our detection statistics, we perform a number of monte-carlo simulations. We produce sensitivity curves for PTAs of various configurations, and outline an implementation of a fully functional data analysis pipeline. Finally, we present a derivation of the likelihood maximized over the gravitational wave phases at the pulsar locations, which results in a vast reduction of the search parameter space.

#### May 18, 2012

1204.4218 (/preprints)
2012-05-18, 18:17 

## [1204.4340] Light scalar field constraints from gravitational-wave observations of compact binaries

Authors: Emanuele Berti, Leonardo Gualtieri, Michael Horbatsch, Justin Alsing

Date: 19 Apr 2012

Abstract: Scalar-tensor theories are among the simplest extensions of general relativity. In theories with light scalars, deviations from Einstein's theory of gravity are determined by the scalar mass m_s and by a Brans-Dicke-like coupling parameter \omega_{BD}. We show that gravitational-wave observations of nonspinning neutron star-black hole binary inspirals can be used to set upper bounds on the combination m_s/\sqrt{\omega_{BD}}. We estimate via a Fisher matrix analysis that individual observations with signal-to-noise ratio \rho would yield (m_s/\sqrt{\omega_{\rm BD}})(\rho/10)\lesssim 10ˆ{-15}, 10ˆ{-16} and 10ˆ{-19} eV for Advanced LIGO, ET and eLISA, respectively. A statistical combination of multiple observations may further improve this bound.

#### May 18, 2012

1204.4340 (/preprints)
2012-05-18, 18:17 

## [1204.4510] Optimizing optical follow-up of gravitational-wave candidates

Authors: Leo Singer, Larry Price, Antony Speranza

Date: 20 Apr 2012

Abstract: Observations with interferometric gravitational-wave detectors result in probability sky maps that are multimodal and spread over 10-100 degˆ2. We present a scheme for maximizing the probability of imaging optical counterparts to gravitational-wave transients given limited observing resources. Our framework is capable of coordinating many telescopes with different fields of view and limiting magnitudes. We present a case study comparing three different planning algorithms. We find that, with the network of telescopes that was used in the most recent joint LIGO-Virgo science run, a relatively straightforward coordinated approach doubles the detection efficiency relative to each telescope observing independently.

#### May 18, 2012

1204.4510 (/preprints)
2012-05-18, 18:15 

## [1205.3112] Treatment of Calibration Uncertainty in Multi-Baseline Cross-Correlation Searches for Gravitational Waves

Authors: John T. Whelan, Emma L. Robinson, Joseph D. Romano, Eric H. Thrane

Date: 14 May 2012

Abstract: Residual uncertainty in the calibration of gravitational wave (GW) detector data leads to systematic errors which must be accounted for in setting limits on the strength of GW signals. When cross-correlation measurements are made using data from a pair of instruments, as in searches for a stochastic GW background, the calibration uncertainties associated with the two instruments can be combined into an uncertainty associated with the pair. With the advent of multi-baseline GW observation (e.g., networks consisting of multiple detectors such as the LIGO observatories and Virgo), a more sophisticated treatment is called for. We describe how the correlations between calibration factors associated with different pairs can be taken into account by marginalizing over the uncertainty associated with each instrument, defining two methods known as per-baseline and per-instrument marginalization.

#### May 18, 2012

1205.3112 (/preprints)
2012-05-18, 18:13 

## [1205.3403] Tidal effects in binary neutron star coalescence

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Marcus Thierfelder, Bernd Bruegmann

Date: 15 May 2012

Abstract: We compare dynamics and waveforms from binary neutron star coalescence as computed by new long-term ($\sim 10$ orbits) numerical relativity simulations and by the tidal effective-one-body (EOB) model including analytical tidal corrections up to second post-Newtonian order (2PN). The current analytical knowledge encoded in the tidal EOB model is found to be sufficient to reproduce the numerical data up to contact and within their uncertainties. Remarkably, no calibration of any tidal EOB free parameters is required, beside those already fitted to binary black holes data. The inclusion of 2PN tidal corrections minimizes the differences with the numerical data, but it is not possible to significantly distinguish them from the leading-order tidal contribution. The presence of a relevant amplification of tidal effects is likely to be excluded, although it can appear as a consequence of numerical inaccuracies. We conclude that the tidally-completed effective-one-body model provides nowadays the most advanced and accurate tool for modelling gravitational waveforms from binary neutron star inspiral up to contact. This work also points out the importance of extensive tests to assess the uncertainties of the numerical data, and the potential need of new numerical strategies to perform accurate simulations.

#### May 18, 2012

1205.3403 (/preprints)
2012-05-18, 18:12 

## [1205.3365] Everything You Always Wanted To Know About The Cosmological Constant Problem (But Were Afraid To Ask)

Authors: Jerome Martin (Institut d&#x27;Astrophysique de Paris)

Date: 15 May 2012

Abstract: This article aims at discussing the cosmological constant problem at a pedagogical but fully technical level. We review how the vacuum energy can be regularized in flat and curved space-time and how it can be understood in terms of Feynman bubble diagrams. In particular, we show that the properly renormalized value of the zero-point energy density today (for a free theory) is in fact far from being 122 orders of magnitude larger than the critical energy density, as often quoted in the literature. We mainly consider the case of scalar fields but also treat the cases of fermions and gauge bosons which allows us to discuss the question of vacuum energy in super-symmetry. Then, we discuss how the cosmological constant can be measured in cosmology and constrained with experiments such as measurements of planet orbits in our solar system or atomic spectra. We also review why the Lamb shift and the Casimir effect seem to indicate that the quantum zero-point fluctuations are not an artifact of the quantum field theory formalism. We investigate how experiments on the universality of free fall can constrain the gravitational properties of vacuum energy and we discuss the status of the weak equivalence principle in quantum mechanics, in particular the Collela, Overhausser and Werner experiment and the quantum Galileo experiment performed with a Salecker-Wigner-Peres clock. Finally, we briefly conclude with a discussion on the solutions to the cosmological constant problem that have been proposed so far.

#### May 18, 2012

1205.3365 (/preprints)
2012-05-18, 18:12 

## [1205.3751] Tests of the universality of free fall for strongly self-gravitating bodies with radio pulsars

Authors: Paulo C. C. Freire, Michael Kramer, Norbert Wex

Date: 16 May 2012

Abstract: In this paper, we review tests of the strong equivalence principle (SEP) derived from binary pulsar data. The extreme difference in binding energy between both components and the precise measurement of the orbital motion provided by pulsar timing allow the only current precision SEP tests for strongly self-gravitating bodies. We start by highlighting why such tests are conceptually important. We then review previous work where limits on SEP violation are obtained with an ensemble of wide binary systems with small eccentricity orbits. Then we propose a new SEP violation test based on the measurement of the variation of the orbital eccentricity de/dt. This new method has the following advantages: a) unlike previous methods it is not based on probabilistic considerations, b) it can make a direct detection of SEP violation, c) the measurement of de/dt is not contaminated by any known external effects, which implies that this SEP test is only restricted by the measurement precision of de/dt. In the final part of the review, we conceptually compare the SEP test with the test for dipolar radiation damping, a phenomenon closely related to SEP violation, and speculate on future prospects by new types of tests in globular clusters and future triple systems.

#### May 18, 2012

1205.3751 (/preprints)
2012-05-18, 18:11 

## [1205.3842] Radiation reaction at 3.5 post-Newtonian order in effective field theory

Date: 17 May 2012

Abstract: We derive the radiation reaction forces on a compact binary inspiral through 3.5 order in the post-Newtonian expansion using the effective field theory approach. We utilize a recent formulation of Hamilton's variational principle that rigorously extends the usual Lagrangian and Hamiltonian formalisms to dissipative systems, including the inspiral of a compact binary from the emission of gravitational waves. We find agreement with previous results, which thus provides a non-trivial confirmation of the extended variational principle. The results from this work nearly complete the equations of motion for the generic inspiral of a compact binary with spinning constituents through 3.5 post-Newtonian order, as derived entirely with effective field theory, with only the spin-orbit corrections to the potential at 3.5 post-Newtonian remaining.

#### May 18, 2012

1205.3842 (/preprints)
2012-05-18, 18:09 

## [1204.6242] The Electromagnetic Signals of Compact Binary Mergers

Authors: T. Piran, E. Nakar, S. Rosswog

Date: 27 Apr 2012

Abstract: Compact binary mergers are prime sources of gravitational waves (GWs), targeted by current and next generation detectors. The question "what is the observable electromagnetic (EM) signature of a compact binary merger?" is an intriguing one with crucial consequences to the quest for gravitational waves. We present a large set of numerical simulations that focus on the electromagnetic signals that emerge from the dynamically ejected sub-relativistic material. These outflows produce on a time scale of a day macronovae - short-lived optical/UV signals powered by radioactive decay. In addition, the outflow interaction with the surrounding matter inevitably leads to a long-lasting radio emission. We calculate the expected radio signals from these outflows on time scales longer than a year, when the sub-relativistic ejecta dominate the emission. We discuss their detectability in 1.4 GHz and 150 MHz and compare it with an updated estimate of the detectability of short GRBs' orphan afterglows. We find that mergers with characteristics similar to those of the Galactic neutron star binary population (similar masses and typical circum-merger Galactic disk density of $1 {\rm cmˆ{-3}}$) that take place at the detection horizon of advanced GW detectors (300 Mpc) yield 1.4 GHz [150 MHz] signals of $\sim 50$ [300] $\mu$Jy, for several years. The signal on time scales of weeks, is dominated by the mildly and/or ultra relativistic outflow, which is not accounted for by our simulations, and is expected to be even brighter. Upcoming all sky surveys are expected to detect a few dozen, and possibly more, merger remnants at any given time thereby providing robust merger rate estimates even before the advanced GW detectors become operational. The macronovae signals from the same distance peak in the optical/UV at an observed magnitude of 22-23 about 10 hours after the merger.

#### May 11, 2012

1204.6242 (/preprints)
2012-05-11, 18:36 

## [1204.6240] The multi-messenger picture of compact object encounters: binary mergers versus dynamical collisions

Authors: S. Rosswog, T. Piran, E. Nakar

Date: 27 Apr 2012

Abstract: We explore the multi-messenger signatures of encounters between two neutron stars and between a neutron star and a stellar-mass black hole. We focus on the differences between gravitational wave driven binary mergers and dynamical collisions that occur, for example, in globular clusters. For both types of encounters we compare the gravitational wave and neutrino emission properties. We also calculate fallback rates and analyze the properties of the dynamically ejected matter. Last but not least we address the electromagnetic transients that accompany each type of encounter.
The canonical nsns merger case ejects more than 1% of a solar mass of extremely neutron-rich ($Y_e\sim 0.03$) material, an amount that is consistent with double neutron star mergers being a major source of r-process in the galaxy. nsbh collisions eject very large amounts of matter ($\sim 0.15$ \msun) which seriously constrains their admissible occurrence rates. The compact object {\em collision} rate must therefore be less, likely much less, than 10% of the nsns {\em merger} rate. The radioactively decaying ejecta produce optical-UV "macronova" which, for the canonical merger case, peak after $\sim 0.4$ days with a luminosity of $\sim 10ˆ{42}$ erg/s. nsns (nsbh) collisions reach up to 3 (7) times larger peak luminosities. The dynamic ejecta deposit a kinetic energy comparable to a supernova in the ambient medium. The canonical merger case releases approximately $2 \times 10ˆ{50}$ erg, the most extreme (but likely rare) cases deposit kinetic energies of up to $10ˆ{52}$ erg. The deceleration of this mildly relativistic material by the ambient medium produces long lasting radio flares. A canonical ns$ˆ2$ merger at the detection horizon of advanced LIGO/Virgo produces a radio flare that peaks on a time scale of one year with a flux of $\sim$0.1 mJy at 1.4 GHz.

#### May 11, 2012

1204.6240 (/preprints)
2012-05-11, 18:36 

## [1204.6739] Cosmology with the lights off: standard sirens in the Einstein Telescope era

Authors: Stephen R. Taylor, Jonathan R. Gair

Date: 30 Apr 2012

Abstract: We explore the prospects for constraining cosmology using gravitational wave (GW) observations of neutron star binaries by the proposed Einstein Telescope (ET), exploiting the narrowness of the neutron star mass function. Double neutron star (DNS) binaries are expected to be one of the first sources detected after "first-light" of Advanced LIGO and are expected to be detected at a rate of a few tens per year in the advanced era. However the proposed Einstein Telescope (ET) could catalogue tens of thousands per year. Combining the measured source redshift distributions with GW-network distance determinations will permit not only the precision measurement of background cosmological parameters, but will provide an insight into the astrophysical properties of these DNS systems. Of particular interest will be to probe the distribution of delay times between DNS-binary creation and subsequent merger, as well as the evolution of the star-formation rate density within ET's detection horizon. Keeping H_0, Omega_{m,0} and Omega_{\Lambda,0} fixed and investigating the precision with which the dark energy equation-of-state parameters could be recovered, we found that with 10ˆ5 detected DNS binaries we could constrain these parameters to an accuracy similar to forecasted constraints from future CMB+BAO+SNIa measurements. Furthermore, modeling the merger delay-time distribution as a power-law, and the star-formation rate (SFR) density as a parametrised version of the Porciani and Madau SF2 model, we find that the associated astrophysical parameters are constrained to within ~ 10%. All parameter precisions scaled as 1/sqrt(N), where N is the number of catalogued detections. We also investigated how precisions varied with the intrinsic underlying properties of the Universe and with the distance reach of the network (which may be affected by the lower frequency cutoff of the detector).

#### May 11, 2012

1204.6739 (/preprints)
2012-05-11, 18:35 

## [1205.1450] The relativistic pulsar-white dwarf binary PSR J1738 0333 II. The most stringent test of scalar-tensor gravity

Authors: Paulo C. C. Freire, Norbert Wex, Gilles Esposito-Far&#xe8;se, Joris P. W. Verbiest, Matthew Bailes, Bryan A. Jacoby, Michael Kramer, Ingrid H. Stairs, John Antoniadis, Gemma H. Janssen

Date: 7 May 2012

Abstract: (abridged) We report the results of a 10-year timing campaign on PSR J1738+0333, a 5.85-ms pulsar in a low-eccentricity 8.5-hour orbit with a low-mass white dwarf companion (…) The measurements of proper motion and parallax allow for a precise subtraction of the kinematic contribution to the observed orbital decay; this results in a significant measurement of the intrinsic orbital decay: (-25.9 +/- 3.2) \times 10ˆ{-15} s/s. This is consistent with the orbital decay from the emission of gravitational waves predicted by general relativity, (-27.7 +1.5/-1.9) \times 10ˆ{-15} s/s (…). This agreement introduces a tight upper limit on dipolar gravitational wave emission, a prediction of most alternative theories of gravity for asymmetric binary systems such as this. We use this limit to derive the most stringent constraints ever on a wide class of gravity theories, where gravity involves a scalar field contribution. When considering general scalar-tensor theories of gravity, our new bounds are more stringent than the best current solar-system limits over most of the parameter space, and constrain the matter-scalar coupling constant {\alpha}_0ˆ2 to be below the 10ˆ{-5} level. For the special case of the Jordan-Fierz-Brans-Dicke, we obtain the one-sigma bound {\alpha}_0ˆ2 < 2 \times 10ˆ{-5}, which is within a factor two of the Cassini limit. We also use our limit on dipolar gravitational wave emission to constrain a wide class of theories of gravity which are based on a generalization of Bekenstein's Tensor-Vector-Scalar gravity (TeVeS), a relativistic formulation of Modified Newtonian Dynamics (MOND).

#### May 11, 2012

1205.1450 (/preprints)
2012-05-11, 17:12 

## [1205.1253] Testing Chern-Simons Modified Gravity with Gravitational-Wave Detections of Extreme-Mass-Ratio Binaries

Authors: Priscilla Canizares (1,2), Jonathan R. Gair (1), Carlos F. Sopuerta (2) ((1) IoA, Cambridge, (2) ICE, CSIC-IEEC)

Date: 6 May 2012

Abstract: [abridged] The detection of gravitational waves from extreme-mass-ratio (EMRI) binaries, comprising a stellar-mass compact object orbiting around a massive black hole, is one of the main targets for low-frequency gravitational-wave detectors in space, like the Laser Interferometer Space Antenna (LISA or eLISA/NGO). The long-duration gravitational-waveforms emitted by such systems encode the structure of the strong field region of the massive black hole, in which the inspiral occurs. The detection and analysis of EMRIs will therefore allow us to study the geometry of massive black holes and determine whether their nature is as predicted by General Relativity and even to test whether General Relativity is the correct theory to describe the dynamics of these systems. To achieve this, EMRI modeling in alternative theories of gravity is required to describe the generation of gravitational waves. In this paper, we explore to what extent EMRI observations with LISA or eLISA/NGO might be able to distinguish between General Relativity and a particular modification of it, known as Dynamical Chern-Simons Modified Gravity. Our analysis is based on a parameter estimation study that uses approximate gravitational waveforms obtained via a radiative-adiabatic method and is restricted to a five-dimensional subspace of the EMRI configuration space. This includes a Chern-Simons parameter that controls the strength of gravitational deviations from General Relativity. We find that, if Dynamical Chern-Simons Modified Gravity is the correct theory, an observatory like LISA or even eLISA/NGO should be able to measure the Chern-Simons parameter with fractional errors below 5%. If General Relativity is the true theory, these observatories should put bounds on this parameter at the level xiˆ(¼) < 10ˆ4 km, which is four orders of magnitude better than current Solar System bounds.

#### May 11, 2012

1205.1253 (/preprints)
2012-05-11, 17:11 

## [1205.1236] Self-force as probe of internal structure

Authors: Soichiro Isoyama, Eric Poisson

Date: 6 May 2012

Abstract: The self-force acting on a (scalar or electric) charge held in place outside a massive body contains information about the body's composition, and can therefore be used as a probe of internal structure. We explore this theme by computing the (scalar or electromagnetic) self-force when the body is a spherical ball of perfect fluid in hydrostatic equilibrium, under the assumption that its rest-mass density and pressure are related by a polytropic equation of state. The body is strongly self-gravitating, and all computations are performed in exact general relativity. The dependence on internal structure is best revealed by expanding the self-force in powers of 1/r, with r denoting the radial position of the charge outside the body. To the leading order, the self-force scales as 1/rˆ3 and depends only on the square of the charge and the body's mass; the leading self-force is universal. The dependence on internal structure is seen at the next order, 1/rˆ5, through a structure factor that depends on the equation of state. We compute this structure factor for relativistic polytropes, and show that for a fixed mass, it increases linearly with the body's radius in the case of the scalar self-force, and quadratically with the body's radius in the case of the electromagnetic self-force. In both cases we find that for a fixed mass and radius, the self-force is smaller if the body is more centrally dense, and larger if the mass density is more uniformly distributed.

#### May 11, 2012

1205.1236 (/preprints)
2012-05-11, 17:11 

## [1205.1124] Swift follow-up observations of candidate gravitational-wave transient events

Date: 5 May 2012

Abstract: We present the first multi-wavelength follow-up observations of two candidate gravitational-wave (GW) transient events recorded by LIGO and Virgo in their 2009-2010 science run. The events were selected with low latency by the network of GW detectors and their candidate sky locations were observed by the Swift observatory. Image transient detection was used to analyze the collected electromagnetic data, which were found to be consistent with background. Off-line analysis of the GW data alone has also established that the selected GW events show no evidence of an astrophysical origin; one of them is consistent with background and the other one was a test, part of a "blind injection challenge". With this work we demonstrate the feasibility of rapid follow-ups of GW transients and establish the sensitivity improvement joint electromagnetic and GW observations could bring. This is a first step toward an electromagnetic follow-up program in the regime of routine detections with the advanced GW instruments expected within this decade. In that regime multi-wavelength observations will play a significant role in completing the astrophysical identification of GW sources. We present the methods and results from this first combined analysis and discuss its implications in terms of sensitivity for the present and future instruments.

#### May 11, 2012

1205.1124 (/preprints)
2012-05-11, 17:10 

## [1205.1512] Large-Scale Structure with Gravitational Waves I: Galaxy Clustering

Authors: Donghui Jeong, Fabian Schmidt

Date: 7 May 2012

Abstract: Observed angular positions and redshifts of large-scale structure tracers such as galaxies are affected by gravitational waves through volume distortion and magnification effects. Thus, a gravitational wave background can in principle be probed through clustering statistics of large-scale structure. We calculate the observed angular clustering of galaxies in the presence of a gravitational wave background at linear order including all relativistic effects. For a scale-invariant spectrum of gravitational waves, the effects are most significant at the smallest multipoles (2 <= l <= 5), but typically suppressed by six or more orders of magnitude with respect to scalar contributions for currently allowed amplitudes of the inflationary gravitational wave background. We also discuss the most relevant second-order terms, corresponding to the distortion of tracer correlation functions by gravitational waves. These provide a natural application of the approach recently developed in arXiv:1204.3625.

#### May 11, 2012

1205.1512 (/preprints)
2012-05-11, 17:09 

## [1205.1613] Constraining massive gravity with recent cosmological data

Authors: Vincenzo F. Cardone, Ninfa Radicella, Luca Parisi

Date: 8 May 2012

Abstract: A covariant formulation of a theory with a massive graviton and no negative energy state has been recently proposed as an alternative to the usual General Relativity framework. For a spatially flat homogenous and isotropic universe, the theory introduces modified Friedmann equations where the standard matter term is supplemented by four effective fluids mimicking dust, cosmological constant, quintessence and stiff matter, respectively. We test the viability of this massive gravity formulation by contrasting its theoretical prediction to the Hubble diagram as traced by Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the $H(z)$ measurements from passively evolving galaxies, Baryon Acoustic Oscillations (BAOs) from galaxy surveys and the distance priors from the Cosmic Microwave Background Radiation (CMBR) anisotropy spectrum. It turns out that the model is indeed able to very well fit this large dataset thus offering a viable alternative to the usual dark energy framework. We finally set stringent constraints on its parameters also narrowing down the allowed range for the graviton mass.

#### May 11, 2012

1205.1613 (/preprints)
2012-05-11, 17:09 

## [1205.1514] Large-Scale Structure with Gravitational Waves II: Shear

Authors: Fabian Schmidt, Donghui Jeong

Date: 7 May 2012

Abstract: The B-(curl-)mode of the correlation of galaxy ellipticities (shear) can be used to detect a stochastic gravitational wave background, such as that predicted by inflation. In this paper, we derive the tensor mode contributions to shear from both gravitational lensing and intrinsic alignments, using the gauge-invariant, full-sky results of arXiv:1204.3625. We find that the intrinsic alignment contribution, calculated using the linear alignment model, is larger than the lensing contribution by an order of magnitude or more, if the alignment strength for tensor modes is of the same order as for scalar modes. This contribution also extends to higher multipoles. These results make the prospects for probing tensor modes using galaxy surveys less pessimistic than previously thought, though still very challenging.

#### May 11, 2012

1205.1514 (/preprints)
2012-05-11, 17:09 

## [1205.2287] Asymptotic frame selection for binary black hole spacetimes II: Post-Newtonian limit

Authors: Evan Ochsner, Richard O&#x27;Shaughnessy (UWM)

Date: 10 May 2012

Abstract: One way to select a preferred frame from gravitational radiation is via the principal axes of < L L>, an average of the action of rotation group generators on the Weyl tensor at asymptotic infinity. In this paper we evaluate this time-domain average for a quasicircular binary using approximate (post-Newtonian) waveforms. For nonprecessing unequal-mass binaries, we show the dominant eigenvector of this tensor lies along the orbital angular momentum. For precessing binaries, this frame is not generally aligned with either the orbital or total angular momentum, working to leading order in the spins. The difference between these two quantities grows with time, as the binary approaches the end of the inspiral and both precession and higher harmonics become more significant.

#### May 11, 2012

1205.2287 (/preprints)
2012-05-11, 16:56 

## [1204.4321] The optimal schedule for pulsar timing array observations

Authors: K. J. Lee, C. G. Bassa, R. Karuppusamy, M. Kramer, R. Smits, B. W.Stappers

Date: 19 Apr 2012

Abstract: In order to maximize the sensitivity of pulsar timing arrays to a stochastic gravitational wave background, we present computational techniques to optimize observing schedules. The techniques are applicable to both single and multi-telescope experiments. The observing schedule is optimized for each telescope by adjusting the observing time allocated to each pulsar while keeping the total amount of observing time constant. The optimized schedule depends on the timing noise characteristics of each individual pulsar as well as the performance of instrumentation. Several examples are given to illustrate the effects of different types of noise. A method to select the most suitable pulsars to be included in a pulsar timing array project is also presented.

#### Apr 23, 2012

1204.4321 (/preprints)
2012-04-23, 16:40 

## [1204.3858] Binary Neutron Star Mergers

Authors: Joshua A. Faber, Frederic A. Rasio

Date: 17 Apr 2012

Abstract: We review the current status of studies of the coalescence of binary neutron star systems. We begin with a discussion of the formation channels of merging binaries and we discuss the most recent theoretical predictions for merger rates. Next, we turn to the quasi-equilibrium formalisms that are used to study binaries prior to the merger phase and to generate initial data for fully dynamical simulations. The quasi-equilibrium approximation has played a key role in developing our understanding of the physics of binary coalescence and, in particular, of the orbital instability processes that can drive binaries to merger at the end of their lifetimes. We then turn to the numerical techniques used in dynamical simulations, including relativistic formalisms, (magneto-)hydrodynamics, gravitational-wave extraction techniques, and nuclear microphysics treatments. This is followed by a summary of the simulations performed across the field to date, including the most recent results from both fully relativistic and microphysically detailed simulations. Finally, we discuss the likely directions for the field as we transition from the first to the second generation of gravitational-wave interferometers and while supercomputers reach the petascale frontier.

#### Apr 19, 2012

1204.3858 (/preprints)
2012-04-19, 11:19 

## [1204.4110] Gravitational waves and gamma-ray bursts

Authors: Alessandra Corsi, for the LIGO Scientific Collaboration, for the Virgo Collaboration

Date: 18 Apr 2012

Abstract: Gamma-Ray Bursts are likely associated with a catastrophic energy release in stellar mass objects. Electromagnetic observations provide important, but indirect information on the progenitor. On the other hand, gravitational waves emitted from the central source, carry direct information on its nature. In this context, I give an overview of the multi-messenger study of gamma-ray bursts that can be carried out by using electromagnetic and gravitational wave observations. I also underline the importance of joint optical and gravitational wave searches, in the absence of a gamma-ray trigger. Finally, I discuss how multi-messenger observations may probe alternative gamma-ray burst progenitor models, such as the magnetar scenario.

#### Apr 19, 2012

1204.4110 (/preprints)
2012-04-19, 11:18 

## [1204.3781] Gravitational waves from color-magnetic mountains' in neutron stars

Authors: K. Glampedakis, D.I. Jones, L. Samuelsson

Date: 17 Apr 2012

Abstract: Neutron stars may harbour the true ground state of matter in the form of strange quark matter. If present, this type of matter is expected to be a color superconductor, a consequence of quark pairing with respect to the color/flavor degrees of freedom. The stellar magnetic field threading the quark core becomes a color-magnetic admixture and, in the event that superconductivity is of type II, leads to the formation of color-magnetic vortices. In this Letter we show that the volume-averaged color-magnetic vortex tension force should naturally lead to a significant degree of non-axisymmetry in systems like radio pulsars. We show that gravitational radiation from such color-magnetic ‘mountains’ in young pulsars like the Crab and Vela could be observable by the future Einstein Telescope, thus becoming a probe of paired quark matter in neutron stars. The detectability threshold can be pushed up toward the sensitivity level of Advanced LIGO if we invoke an interior magnetic field about a factor ten stronger than the surface polar field.

#### Apr 19, 2012

1204.3781 (/preprints)
2012-04-19, 11:18 

## [1204.3948] The relativistic pulsar-white dwarf binary PSR J1738 0333 I. Mass determination and evolutionary history

Authors: J. Antoniadis, M. H. van Kerkwijk, D. Koester, P. C. C. Freire, N. Wex, T. M. Tauris, M. Kramer, C. G. Bassa

Date: 18 Apr 2012

Abstract: PSR J1738+0333 is one of the four millisecond pulsars known to be orbited by a white dwarf companion bright enough for optical spectroscopy. Of these, it has the shortest orbital period, making it especially interesting for a range of astrophysical and gravity related questions. We present a spectroscopic and photometric study of the white dwarf companion and infer its radial velocity curve, effective temperature, surface gravity and luminosity. We find that the white dwarf has properties consistent with those of low-mass white dwarfs with thick hydrogen envelopes, and use the corresponding mass-radius relation to infer its mass; M_WD = 0.181 +/- +0.007/-0.005 solar masses. Combined with the mass ratio q=8.1 +/- 0.2 inferred from the radial velocities and the precise pulsar timing ephemeris, the neutron star mass is constrained to M_PSR = 1.47 +/- +0.07/-0.06 solar masses. Contrary to expectations, the latter is only slightly above the Chandrasekhar limit. We find that, even if the birth mass of the neutron star was only 1.20 solar masses, more than 60% of the matter that left the surface of the white dwarf progenitor escaped the system. The accurate determination of the component masses transforms this system in a laboratory for fundamental physics by constraining the orbital decay predicted by general relativity. Currently, the agreement is within 1 sigma of the observed decay. Further radio timing observations will allow precise tests of white dwarf models, assuming the validity of general relativity.

#### Apr 19, 2012

1204.3948 (/preprints)
2012-04-19, 11:17 

## [1204.2507] Support for the thermal origin of the Pioneer anomaly

Authors: Slava G. Turyshev, Viktor T. Toth, Gary Kinsella, Siu-Chun Lee, Shing M. Lok, Jordan Ellis

Date: 11 Apr 2012

Abstract: We investigate the possibility that the anomalous acceleration of the Pioneer 10 and 11 spacecraft is due to the recoil force associated with an anisotropic emission of thermal radiation off the vehicles. To this end, relying on the project and spacecraft design documentation, we constructed a comprehensive finite-element thermal model of the two spacecraft. Then, we numerically solve thermal conduction and radiation equations using the actual flight telemetry as boundary conditions. We use the results of this model to evaluate the effect of the thermal recoil force on the Pioneer 10 spacecraft at various heliocentric distances. We found that the magnitude, temporal behavior, and direction of the resulting thermal acceleration are all similar to the properties of the observed anomaly. As a novel element of our investigation, we develop a parameterized model for the thermal recoil force and estimate the coefficients of this model independently from navigational Doppler data. We find no statistically significant difference between the two estimates and conclude that once the thermal recoil force is properly accounted for, no anomalous acceleration remains.

#### Apr 16, 2012

1204.2507 (/preprints)
2012-04-16, 12:11 

## [1204.2585] Model-Independent Test of General Relativity: An Extended post-Einsteinian Framework with Complete Polarization Content

Authors: Katerina Chatziioannou, Nicolas Yunes, Neil Cornish

Date: 11 Apr 2012

Abstract: We develop a model-independent test of General Relativity that allows for the constraint of the gravitational wave (GW) polarization content with GW detections of binary compact object inspirals. We first consider three modified gravity theories (Brans-Dicke theory, Rosen's theory and Lightman-Lee theory) and calculate the response function of ground-based detectors to gravitational waves in the inspiral phase. This allows us to see how additional polarizations predicted in these theories modify the General Relativistic prediction of the response function. We then consider general power-law modifications to the Hamiltonian and radiation-reaction force and study how these modify the time-domain and Fourier response function when all polarizations are present. From these general arguments and specific modified gravity examples, we infer an improved parameterized post-Einsteinian template family with complete polarization content. This family enhances General Relativity templates through the inclusion of new theory parameters, reducing to the former when these parameters acquire certain values, and recovering modified gravity predictions for other values, including all polarizations. We conclude by discussing detection strategies to constrain these new, polarization theory parameters by constructing certain null channels through the combination of output from multiple detectors.

#### Apr 16, 2012

1204.2585 (/preprints)
2012-04-16, 12:11 

## [1204.0028] The ELM Survey. IV. 24 White Dwarf Merger Systems

Authors: Mukremin Kilic, Warren R. Brown, Carlos Allende Prieto, S. J. Kenyon, Craig O. Heinke, M. A. Agueros, S. J. Kleinman

Date: 30 Mar 2012

Abstract: We present new radial velocity and X-ray observations of extremely low-mass (ELM, 0.2 Msol) white dwarf candidates in the Sloan Digital Sky Survey (SDSS) Data Release 7 area. We identify seven new binary systems with 1-18 h orbital periods. Five of the systems will merge due to gravitational wave radiation within 10 Gyr, bringing the total number of merger systems found in the ELM Survey to 24. The ELM Survey has now quintupled the known merger white dwarf population. It has also discovered the eight shortest period detached binary white dwarf systems currently known. We discuss the characteristics of the merger and non-merger systems observed in the ELM Survey, including their future evolution. About half of the systems have extreme mass ratios. These are the progenitors of the AM Canum Venaticorum systems and supernovae .Ia. The remaining targets will lead to the formation of extreme helium stars, subdwarfs, or massive white dwarfs. We identify three targets that are excellent gravitational wave sources. These should be detected by the Laser Interferometer Space Antenna (LISA)-like missions within the first year of operation. The remaining targets are important indicators of what the Galactic foreground may look like for gravitational wave observatories.

#### Apr 16, 2012

1204.0028 (/preprints)
2012-04-16, 08:53 

## [1204.1073] Circumbinary MHD Accretion into Inspiraling Binary Black Holes

Authors: Scott C. Noble (1), Bruno C. Mundim (1), Hiroyuki Nakano (1), Julian H. Krolik (2), Manuela Campanelli (1), Yosef Zlochower (1), Nicol&#xe1;s Yunes (3) ((1) Rochester Institute of Technology, (2) Johns Hopkins University, (3) Montana State University)

Date: 4 Apr 2012

Abstract: As 2 black holes bound to each other in a close binary approach merger their inspiral time becomes shorter than the characteristic inflow time of surrounding orbiting matter. Using an innovative technique in which we represent the changing spacetime in the region occupied by the orbiting matter with a 2.5PN approximation and the binary orbital evolution with 3.5PN, we have simulated the MHD evolution of a circumbinary disk surrounding an equal-mass non-spinning binary. Prior to the beginning of the inspiral, the structure of the circumbinary disk is predicted well by extrapolation from Newtonian results. The binary opens a low-density gap whose radius is roughly two binary separations, and matter piles up at the outer edge of this gap as inflow is retarded by torques exerted by the binary; nonetheless, the accretion rate is diminished relative to its value at larger radius by only about a factor of 2. During inspiral, the inner edge of the disk at first moves inward in coordination with the shrinking binary, but as the orbital evolution accelerates, the rate at which the inner edge moves toward smaller radii falls behind the rate of binary compression. In this stage, the rate of angular momentum transfer from the binary to the disk slows substantially, but the net accretion rate decreases by only 10-20%. When the binary separation is tens of gravitational radii, the rest-mass efficiency of disk radiation is a few percent, suggesting that supermassive binary black holes in galactic nuclei could be very luminous at this stage of their evolution. If the luminosity were optically thin, it would be modulated at a frequency that is a beat between the orbital frequency of the disk's surface density maximum and the binary orbital frequency. However, a disk with sufficient surface density to be luminous should also be optically thick; as a result, the periodic modulation may be suppressed.

#### Apr 11, 2012

1204.1073 (/preprints)
2012-04-11, 09:27 

## [1204.1888] Equation-of-state dependence of the gravitational-wave signal from the ring-down phase of neutron-star mergers

Authors: A. Bauswein (1), H.-T. Janka (1), K. Hebeler (2), A. Schwenk (3,4) ((1) MPI for Astrophysics, Garching, (2) Ohio State University, Columbus, (3) ExtreMe Matter Institute EMMI, Darmstadt, (4) Technische Universita&#xe4;t Darmstadt)

Date: 9 Apr 2012

Abstract: Neutron-star (NS) merger simulations are conducted for 38 representative microphysical descriptions of high-density matter in order to explore the equation-of-state dependence of the postmerger ring-down phase. The formation of a deformed, oscillating, differentially rotating very massive NS is the typical outcome of the coalescence of two stars with 1.35 $M_{\odot}$ for most candidate EoSs. The oscillations of this object imprint a pronounced peak in the gravitational-wave (GW) spectra, which is used to characterize the emission for a given model. The peak frequency of this postmerger GW signal correlates very well with the radii of nonrotating NSs, and thus allows to constrain the high-density EoS by a GW detection. In the case of 1.35-1.35 $M_{\odot}$ mergers the peak frequency scales particularly well with the radius of a NS with 1.6 $M_{\odot}$, where the maximum deviation from this correlation is only 60 meters for fully microphysical EoSs which are compatible with NS observations. Combined with the uncertainty in the determination of the peak frequency it appears likely that a GW detection can measure the radius of a 1.6 $M_{\odot}$ NS with an accuracy of about 100 to 200 meters. We also uncover relations of the peak frequency with the radii of nonrotating NSs with 1.35 $M_{\odot}$ or 1.8 $M_{\odot}$, with the radius or the central energy density of the maximum-mass Tolman-Oppenheimer-Volkoff configuration, and with the pressure or sound speed at a fiducial rest-mass density of about twice nuclear saturation density. Furthermore, it is found that a determination of the dominant postmerger GW frequency can provide an upper limit for the maximum mass of nonrotating NSs. The prospects for a detection of the postmerger GW signal and a determination of the dominant GW frequency are estimated to be in the range of 0.015 to 1.2 events per year with the upcoming Advanced LIGO detector.

#### Apr 11, 2012

1204.1888 (/preprints)
2012-04-11, 09:25 

## [1204.1859] Equivalence Principles, Lense-Thirring Effects, and Solar-System Tests of Cosmological Models

Authors: Wei-Tou Ni

Date: 9 Apr 2012

Abstract: In this talk, we review the empirical status for modern gravitational theories with emphases on (i) Equivalence Principles; (ii) Lense-Thirring effects and the implications of Gravity Probe B experiment; (iii) Solar-System Tests of Cosmological Models.

#### Apr 11, 2012

1204.1859 (/preprints)
2012-04-11, 09:25 

## [1204.1670] Probing the Inhomogeneous Universe with Gravitational Wave Cosmology

Authors: Kent Yagi, Atsushi Nishizawa, Chul-Moon Yoo

Date: 7 Apr 2012

Abstract: If we assume that we live in the center of a spherical inhomogeneous universe, we can explain the apparent accelerating expansion of the universe without introducing the unknown dark energy or modifying gravitational theory. Direct measurement of the cosmic acceleration can be a powerful tool in distinguishing $\Lambda$CDM and the inhomogeneous models. If $\Lambda$CDM is the correct model, we have shown that DECIGO/BBO has sufficient ability to detect the positive redshift drift of the source by observing gravitational waves from neutron star binaries for 5-10 years. This enables us to rule out any Lema\ˆitre-Tolman-Bondi (LTB) void model with monotonically increasing density profile. Furthermore, by detecting the positive redshift drift at $z\sim 0$, we can even rule out generic LTB models unless we allow unrealistically steep density gradient at $z\sim 0$. We also show that the measurement accuracy is slightly improved when we consider the joint search of DECIGO/BBO and the third generation Einstein Telescope. This test can be performed with GW observations alone without any reference to electromagnetic observations.

#### Apr 11, 2012

1204.1670 (/preprints)
2012-04-11, 09:24 

## [1204.2000] Gravitational Wave Astronomy: Needle in a Haystack

Authors: Neil J. Cornish

Date: 9 Apr 2012

Abstract: A world-wide array of highly sensitive interferometers stands poised to usher in a new era in astronomy with the first direct detection of gravitational waves. The data from these instruments will provide a unique perspective on extreme astrophysical phenomena such as neutron stars and black holes, and will allow us to test Einstein's theory of gravity in the strong field, dynamical regime. To fully realize these goals we need to solve some challenging problems in signal processing and inference, such as finding rare and weak signals that are buried in non-stationary and non-Gaussian instrument noise, dealing with high-dimensional model spaces, and locating what are often extremely tight concentrations of posterior mass within the prior volume. Gravitational wave detection using space based detectors and Pulsar Timing Arrays bring with them the additional challenge of having to isolate individual signals that overlap one another in both time and frequency. Promising solutions to these problems will be discussed, along with some of the challenges that remain.

#### Apr 11, 2012

1204.2000 (/preprints)
2012-04-11, 09:23 

## [1203.6603] Compact binary coalescence parameter estimations for 2.5 post-Newtonian aligned spinning waveforms

Authors: Alex B. Nielsen

Date: 29 Mar 2012

Abstract: We examine the parameter accuracy that can be achieved by advanced ground-based detectors for binary inspiralling black holes and neutron stars. We use the 2.5 PN spinning waveforms of Arun et al. (2009). Our main result is that the errors are noticeably different from existing 2PN studies for aligned spins. While the masses can be determined more accurately, the individual spins are measured less accurately compared to previous work at lower PN order. We also examine several regions of parameter space relevant to expected sources and the impact of simple priors. A combination of the spins is measurable to higher accuracy and we examine what this can tell us about spinning systems.

#### Apr 05, 2012

1203.6603 (/preprints)
2012-04-05, 09:28 

## [1203.6443] Continuum and Discrete Initial-Boundary-Value Problems and Einstein's Field Equations

Authors: Olivier Sarbach, Manuel Tiglio

Date: 29 Mar 2012

Abstract: Many evolution problems in physics are described by partial differential equations on an infinite domain; therefore, one is interested in the solutions to such problems for a given initial dataset. A prominent example is the binary black hole problem within Einstein's theory of gravitation, in which one computes the gravitational radiation emitted from the inspiral of the two black holes, merger and ringdown. Powerful mathematical tools can be used to establish qualitative statements about the solutions, such as their existence, uniqueness, continuous dependence on the initial data, or their asymptotic behavior over large time scales. However, one is often interested in computing the solution itself, and unless the partial differential equation is very simple, or the initial data possesses a high degree of symmetry, this computation requires approximation by numerical discretization. When solving such discrete problems on a machine, one is faced with a finite limit to computational resources, which leads to the replacement of the infinite continuum domain with a finite computer grid. This, in turn, leads to a discrete initial-boundary value problem. The hope is to recover, with high accuracy, the exact solution in the limit where the grid spacing converges to zero with the boundary being pushed to infinity.
The goal of this article is to review some of the theory necessary to understand the continuum and discrete initial-boundary value problems arising from hyperbolic partial differential equations and to discuss its applications to numerical relativity; in particular, we present well-posed initial and initial-boundary value formulations of Einstein's equations, and we discuss multi-domain high-order finite difference and spectral methods to solve them.

#### Apr 05, 2012

1203.6443 (/preprints)
2012-04-05, 09:28 

## [1203.6352] No Evidence for Intermediate-Mass Black Holes in Globular Clusters: Strong Constraints from the JVLA

Authors: Jay Strader, Laura Chomiuk, Thomas Maccarone, James Miller-Jones, Anil Seth, Craig Heinke, Gregory Sivakoff

Date: 28 Mar 2012

Abstract: With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky VLA radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 uJy/beam at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3-sigma upper limits on IMBHs from 360-980 M_sun. These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (a) IMBHs ~> 1000 M_sun are rare in globular clusters, or (b) when present, IMBHs accrete in an extraordinarily inefficient manner.

#### Apr 05, 2012

1203.6352 (/preprints)
2012-04-05, 09:28 

## [1204.1043] The third and a half post-Newtonian gravitational wave quadrupole mode for quasi-circular inspiralling compact binaries

Authors: Guillaume Faye, Sylvain Marsat, Luc Blanchet, Bala R. Iyer

Date: 4 Apr 2012

Abstract: We compute the quadrupole mode of the gravitational waveform of inspiralling compact binaries at the third and a half post-Newtonian (3.5PN) approximation of general relativity. The computation is performed using the multipolar post-Newtonian formalism, and restricted to binaries without spins moving on quasi-circular orbits. The new inputs mainly include the 3.5PN terms in the mass quadrupole moment of the source, and the control of required subdominant corrections to the contributions of hereditary integrals (tails and non-linear memory effect). The result is given in the form of the quadrupolar mode (2,2) in a spin-weighted spherical harmonic decomposition of the waveform, and will allow a more accurate comparison with the outcome of numerical relativity simulations.

#### Apr 05, 2012

1204.1043 (/preprints)
2012-04-05, 09:25 

## [1203.6685] Binary Disruption by Massive Black Holes: Hypervelocity Stars, S Stars, and Tidal Disruption Events

Authors: Benjamin C. Bromley (1), Scott J. Kenyon (2), Margaret J. Geller (2), Warren R. Brown (2) ((1) University of Utah (2) Smithsonian Astrophysical Observatory)

Date: 29 Mar 2012

Abstract: We examine whether disrupted binary stars can fuel black hole growth. In this mechanism, tidal disruption produces a single hypervelocity star (HVS) ejected at high velocity and a former companion star bound to the black hole. After a cluster of bound stars forms, orbital diffusion allows the black hole to accrete stars by tidal disruption at a rate comparable to the capture rate. In the Milky Way, HVSs and the S star cluster imply similar rates of 10ˆ{-5}--10ˆ{-3} yrˆ{-1} for binary disruption. These rates are consistent with estimates for the tidal disruption rate in nearby galaxies and imply significant black hole growth from disrupted binaries on 10 Gyr time scales.

#### Apr 01, 2012

1203.6685 (/preprints)
2012-04-01, 23:03 

## [1201.1508] An observational test of the Vainshtein mechanism

Authors: Lam Hui, Alberto Nicolis

Date: 6 Jan 2012

Abstract: Modified gravity theories capable of genuine self-acceleration typically invoke a galileon scalar which mediates a long range force, but is screened by the Vainshtein mechanism on small scales. In such theories, non-relativistic stars carry the full scalar charge (proportional to their mass), while black holes carry none. Thus, for a galaxy free-falling in some external gravitational field, its central massive black hole is expected to lag behind the stars. To look for this effect, and to distinguish it from other astrophysical effects, one can correlate the gravitational pull from the surrounding structure with the offset between the stellar center and the black hole. The expected offset depends on the central density of the galaxy, and ranges up to ~0.1 kpc for small galaxies. The observed offset in M87 cannot be explained by this effect unless the scalar force is significantly stronger than gravity. We also discuss the systematic offset of compact objects from the galactic plane as another possible signature.

#### Mar 29, 2012

1201.1508 (/preprints)
2012-03-29, 09:49 

## [1203.6075] The Formation of the First Massive Black Holes

Authors: Zolt&#xe1;n Haiman

Date: 27 Mar 2012

Abstract: Supermassive black holes (SMBHs) are common in local galactic nuclei, and SMBHs as massive as several billion solar masses already exist at redshift z=6. These earliest SMBHs may grow by the combination of radiation-pressure-limited accretion and mergers of stellar-mass seed BHs, left behind by the first generation of metal-free stars, or may be formed by more rapid direct collapse of gas in rare special environments where dense gas can accumulate without first fragmenting into stars. This chapter offers a review of these two competing scenarios, as well as some more exotic alternative ideas. It also briefly discusses how the different models may be distinguished in the future by observations with JWST, (e)LISA and other instruments.

#### Mar 29, 2012

1203.6075 (/preprints)
2012-03-29, 09:49 

## [1203.6108] General Relativistic Simulations of Magnetized Plasmas around Merging Supermassive Black Holes

Authors: Bruno Giacomazzo, John G. Baker, M. Coleman Miller, Christopher S. Reynolds, James R. van Meter

Date: 27 Mar 2012

Abstract: Coalescing supermassive black hole binaries are produced by the mergers of galaxies and are the most powerful sources of gravitational waves accessible to space-based gravitational observatories. Some such mergers may occur in the presence of matter and magnetic fields and hence generate an electromagnetic counterpart. In this paper we present the first general relativistic simulations of magnetized plasma around merging supermassive black holes using the general relativistic magnetohydrodynamic code Whisky. By considering different magnetic field strengths, going from non-magnetically dominated to magnetically dominated regimes, we explore how magnetic fields affect the dynamics of the plasma and the possible emission of electromagnetic signals. In particular we observe a total amplification of the magnetic field of ~2 orders of magnitude which is driven by the accretion onto the binary and that leads to much stronger electromagnetic signals, more than a factor of 10ˆ4 larger than comparable calculations done in the force-free regime where such amplifications are not possible.

#### Mar 29, 2012

1203.6108 (/preprints)
2012-03-29, 09:49 

## [1203.6060] Nonspinning searches for spinning binaries in ground-based detector data: Amplitude and mismatch predictions in the constant precession cone approximation

Authors: D. Brown (1), A. Lundgren (1,2,3), R. O&#x27;Shaughnessy (2,4) ((1) Syracuse University, (2) Penn State University, (3) Albert Einstein Institute, Hannover, (4) University of Wisconsin-Milwaukee)

Date: 27 Mar 2012

Abstract: Current searches for compact binary mergers by ground-based gravitational-wave detectors assume for simplicity the two bodies are not spinning. If the binary contains compact objects with significant spin, then this can reduce the sensitivity of these searches, particularly for black hole--neutron star binaries. In this paper we investigate the effect of neglecting precession on the sensitivity of searches for spinning binaries using non-spinning waveform models. We demonstrate that in the sensitive band of Advanced LIGO, the angle between the binary's orbital angular momentum and its total angular momentum is approximately constant. Under this \emph{constant precession cone} approximation, we show that the gravitational-wave phasing is modulated in two ways: a secular increase of the gravitational-wave phase due to precession and an oscillation around this secular increase. We show that this secular evolution occurs in precisely three ways, corresponding to physically different apparent evolutions of the binary's precession about the line of sight. We estimate the best possible fitting factor between \emph{any} non-precessing template model and a single precessing signal, in the limit of a constant precession cone. Our closed form estimate of the fitting-factor depends only the geometry of the in-band precession cone; it does not depend explicitly on binary parameters, detector response, or details of either signal model. The precessing black hole--neutron star waveforms least accurately matched by nonspinning waveforms correspond to viewing geometries where the precession cone sweeps the orbital plane repeatedly across the line of sight, in an unfavorable polarization alignment.

#### Mar 29, 2012

1203.6060 (/preprints)
2012-03-29, 09:49 

## [1203.5892] Determining gravitational wave radiation from close galaxy pairs using a binary population synthesis approach

Authors: Jinzhong Liu, Yu Zhang, Hailong Zhang, Yutao Sun, Na Wang

Date: 27 Mar 2012

Abstract: Context. The early phase of the coalescence of supermassive black hole (SMBH) binaries from their host galaxies provides a guaranteed source of low-frequency (nHz-$\mu$Hz) gravitational wave (GW) radiation by pulsar timing observations. These types of GW sources would survive the coalescing and be potentially identifiable. Aims. We aim to provide an outline of a new method for detecting GW radiation from individual SMBH systems based on the Sloan Digital Sky Survey (SDSS) observational results, which can be verified by future observations. Methods. Combining the sensitivity of the international Pulsar Timing Array (PTA) and the Square Kilometer Array (SKA) detectors, we used a binary population synthesis (BPS) approach to determine GW radiation from close galaxy pairs under the assumption that SMBHs formed at the core of merged galaxies. We also performed second post-Newtonian approximation methods to estimate the variation of the strain amplitude with time. Results. We find that the value of the strain amplitude \emph{h} varies from about $10ˆ{-14}$ to $10ˆ{-17}$ using the observations of 20 years, and we estimate that about 100 SMBH sources can be detected with the SKA detector.

#### Mar 29, 2012

1203.5892 (/preprints)
2012-03-29, 09:48 

## [1203.5192] Multimessenger astronomy with gravitational waves and high-energy neutrinos

Authors: S. Ando, B. Baret (APC), B. Bouhou (APC), E. Chassande-Mottin (APC), A. Kouchner (APC), L. Moscoso (APC, SEDI), Veronique Van Elewyck (APC), I. Bartos, S. M&#xe1;rka, Z. M&#xe1;rka, A. Corsi, I. Di Palma, M. A. Papa, A. Dietz (LAPP), C. Donzaud (APC), D. Eichler, C. Finley, D. Guetta, F. Halzen, G. Jones, P. J. Sutton, S. Kandhasamy, V. Mandic, E. Thrane, K. Kotake, T. Piran, T. Pradier (IPHC), G. E. Romero, E. Waxman

Date: 23 Mar 2012

Abstract: Many of the astrophysical sources and violent phenomena observed in our Universe are potential emitters of gravitational waves (GW) and high-energy neutrinos (HEN). Both GWs and HENs may escape very dense media and travel unaffected over cosmological distances, carrying information from the innermost regions of the astrophysical engines. Such messengers could also reveal new, hidden sources that have not been observed by conventional photon-based astronomy. Coincident observation of GWs and HENs may thus play a critical role in multimessenger astronomy. This is particularly true at the present time owing to the advent of a new generation of dedicated detectors: IceCube, ANTARES, VIRGO and LIGO. Given the complexity of the instruments, a successful joint analysis of this data set will be possible only if the expertise and knowledge of the data is shared between the two communities. This review aims at providing an overview of both theoretical and experimental state-of-the-art and perspectives for such a GW+HEN multimessenger astronomy.

#### Mar 29, 2012

1203.5192 (/preprints)
2012-03-29, 09:48 

## [1203.4663] Observable Spectra of Induced Gravitational Waves from Inflation

Authors: Laila Alabidi, Kazunori Kohri, Misao Sasaki, Yuuiti Sendouda

Date: 21 Mar 2012

Abstract: Measuring the primordial power spectrum on small scales is a powerful tool in inflation model building, yet constraints from Cosmic Microwave Background measurements alone are insufficient to place bounds stringent enough to be appreciably effective. For the very small scale spectrum, those which subtend angles of less than 0.3 degrees on the sky, an upper bound can be extracted from the astrophysical constraints on the possible production of primordial black holes in the early universe. A recently discovered observational by-product of an enhanced power spectrum on small scales, induced gravitational waves, have been shown to be within the range of proposed space based gravitational wave detectors; such as NASA's LISA and BBO detectors, and the Japanese DECIGO detector. In this paper we explore the impact such a detection would have on models of inflation known to lead to an enhanced power spectrum on small scales, namely the Hilltop-type and running mass models. We find that the Hilltop-type model can produce observable induced gravitational waves within the range of BBO and DECIGO for integral and fractional powers of the potential within a reasonable number of e-folds. We also find that the running mass model can produce a spectrum within the range of these detectors, but require that inflation terminates after an unreasonably small number of e-folds. Finally, we argue that if the thermal history of the Universe were to accomodate such a small number of e-folds the Running Mass Model can produce Primordial Black Holes within a mass range compatible with Dark Matter, i.e. within a mass range 10ˆ{20} g< M_{BH}<10ˆ{27} g.

#### Mar 27, 2012

1203.4663 (/preprints)
2012-03-27, 13:12 

## [1203.5166] Numerical simulations of compact object binaries

Authors: Harald P. Pfeiffer

Date: 23 Mar 2012

Abstract: Coalescing compact object binaries consisting of black holes and/or Neutron stars are a prime target for ground-based gravitational wave detectors. This article reviews the status of numerical simulations of these systems, with an emphasis on recent progress.

#### Mar 26, 2012

1203.5166 (/preprints)
2012-03-26, 12:03 

## [1203.4105] Lorentz breaking Effective Field Theory and observational tests

Authors: Stefano Liberati

Date: 19 Mar 2012

Abstract: Analogue models of gravity have provided an experimentally realizable test field for our ideas on quantum field theory in curved spacetimes but they have also inspired the investigation of possible departures from exact Lorentz invariance at microscopic scales. In this role they have joined, and sometime anticipated, several quantum gravity models characterized by Lorentz breaking phenomenology. A crucial difference between these speculations and other ones associated to quantum gravity scenarios, is the possibility to carry out observational and experimental tests which have nowadays led to a broad range of constraints on departures from Lorentz invariance. We shall review here the effective field theory approach to Lorentz breaking in the matter sector, present the constraints provided by the available observations and finally discuss the implications of the persisting uncertainty on the composition of the ultra high energy cosmic rays for the constraints on the higher order, analogue gravity inspired, Lorentz violations.

#### Mar 21, 2012

1203.4105 (/preprints)
2012-03-21, 13:46 

## [1203.3914] Prospects for an advanced Kennedy-Thorndike experiment in low Earth orbit

Authors: J. A. Lipa, S. Buchman, S. Saraf, J. Zhou, A. Alfauwaz, J. Conklin, G. D. Cutler, R. L. Byer

Date: 18 Mar 2012

Abstract: We discuss the potential for a small space mission to perform an advanced Kennedy-Thorndike test of Special Relativity using the large and rapid velocity modulation available in low Earth orbit. An improvement factor of ~100 over present ground results is expected, with an additional factor of 10 possible using more advanced technology.

#### Mar 21, 2012

1203.3914 (/preprints)
2012-03-21, 13:45 

## [1203.4352] Measurability of the tidal polarizability of neutron stars in late-inspiral gravitational-wave signals

Authors: Thibault Damour, Alessandro Nagar, Loic Villain

Date: 20 Mar 2012

Abstract: The gravitational wave signal from a binary neutron star inspiral contains information on the nuclear equation of state. This information is contained in a combination of the tidal polarizability parameters of the two neutron stars and is clearest in the late inspiral, just before merger. We use the recently defined tidal extension of the effective one-body formalism to construct a controlled analytical description of the frequency-domain phasing of neutron star inspirals up to merger. Exploiting this analytical description we find that the tidal polarizability parameters of neutron stars can be measured by the advanced LIGO-Virgo detector network from gravitational wave signals having a reasonable signal-to-noise ratio of $\rho=16$. This measurability result seems to hold for all the nuclear equations of state leading to a maximum mass larger than $1.97M_\odot$. We also propose a promising new way of extracting information on the nuclear equation of state from a coherent analysis of an ensemble of gravitational wave observations of separate binary merger events.

#### Mar 21, 2012

1203.4352 (/preprints)
2012-03-21, 13:44 

## [1203.3077] Investigating stellar-mass black hole kicks

Authors: Serena Repetto, Melvyn B. Davies, Steinn Sigurdsson

Date: 14 Mar 2012

Abstract: We investigate whether stellar-mass black holes have to receive natal kicks in order to explain the observed distribution of low-mass X-ray binaries containing black holes within our Galaxy. Such binaries are the product of binary evolution, where the massive primary has exploded forming a stellar-mass black hole, probably after a common envelope phase where the system contracted down to separations of order 10-30 Rsun. We perform population synthesis calculations of these binaries, applying both kicks due to supernova mass-loss and natal kicks to the newly-formed black hole. We then integrate the trajectories of the binary systems within the Galactic potential. We find that natal kicks are in fact necessary to reach the large distances above the Galactic plane achieved by some binaries. Further, we find that the distribution of natal kicks would seem to be similar to that of neutron stars, rather than one where the kick velocities are reduced by the ratio of black hole to neutron-star mass (i.e. where the kicks have the same momentum). This result is somewhat surprising; in many pictures of stellar-mass black-hole formation, one might have expected black holes to receive kicks having the same momentum (rather than the same speed) as those given to neutron stars.

#### Mar 16, 2012

1203.3077 (/preprints)
2012-03-16, 18:13 

## [1203.2920] Effects of post-Newtonian Spin Alignment on the Distribution of Black-Hole Recoils

Authors: Emanuele Berti, Michael Kesden, Ulrich Sperhake

Date: 13 Mar 2012

Abstract: Recent numerical relativity simulations have shown that the final black hole produced in a binary merger can recoil with a velocity as large as 5,000 km/s. Because of enhanced gravitational-wave emission in the so-called "hang-up" configurations, this maximum recoil occurs when the black-hole spins are partially aligned with the orbital angular momentum. We revisit our previous statistical analysis of post-Newtonian evolutions of black-hole binaries in the light of these new findings. We demonstrate that despite these new configurations with enhanced recoil velocities, spin alignment during the post-Newtonian stage of the inspiral will still significantly suppress (or enhance) kick magnitudes when the initial spin of the more massive black hole is more (or less) closely aligned with the orbital angular momentum than that of the smaller hole. We present a preliminary study of how this post-Newtonian spin alignment affects the ejection probabilities of supermassive black holes from their host galaxies with astrophysically motivated mass ratio and initial spin distributions. We find that spin alignment suppresses (enhances) ejection probabilities by ~ 40% (20%) for an observationally motivated mass-dependent galactic escape velocity, and by an even greater amount for a constant escape velocity of 1,000 km/s. Kick suppression is thus at least a factor two more efficient than enhancement.

#### Mar 16, 2012

1203.2920 (/preprints)
2012-03-16, 18:12 

## [1203.3090] Thoughts about a conceptual framework for relativistic gravity

Authors: Bernard F. Schutz

Date: 14 Mar 2012

Abstract: I consider the isolation of general relativity research from the rest of theoretical physics during the 1930s-1950s, and the subsequent reinvigoration of the field. I suggest that the main reason for the isolation was that relativists of the time did not develop heuristic concepts about the physics of the theory with which they could communicate with other physicists, and that the revival happened when they began to develop such concepts. A powerful heuristic today is the concept of a black hole, which is a robust and stable component of many astronomical systems. During the 1930s relativists could only offer the "Schwarzschild singularity". I argue that the change occurred at least partly because key theoretical physicists schooled in quantum theory entered relativity research and began to approach problematic issues by asking questions about observable effects and the outcomes of thought experiments. The result was the development of a physical intuition about such things as black holes, which could then be communicated to non-specialists. Only then was it possible to integrate general relativity fully into the rest of physics.

#### Mar 16, 2012

1203.3090 (/preprints)
2012-03-16, 18:12 

## [1203.2856] A new code for parameter estimation in searches for gravitational waves from known pulsars

Authors: M. Pitkin, C. Gill, J. Veitch, E. Macdonald, G. Woan

Date: 13 Mar 2012

Abstract: We describe the consistency testing of a new code for gravitational wave signal parameter estimation in known pulsar searches. The code uses an implementation of nested sampling to explore the likelihood volume. Using fake signals and simulated noise we compare this to a previous code that calculated the signal parameter posterior distributions on both a grid and using a crude Markov chain Monte Carlo (MCMC) method. We define a new parameterisation of two orientation angles of neutron stars used in the signal model (the initial phase and polarisation angle), which breaks a degeneracy between them and allows more efficient exploration of those parameters. Finally, we briefly describe potential areas for further study and the uses of this code in the future.

#### Mar 16, 2012

1203.2856 (/preprints)
2012-03-16, 18:12 

## [1203.2962] Spin induced multipole moments for the gravitational wave amplitude from binary inspirals to 2.5 Post-Newtonian order

Authors: Rafael A. Porto, Andreas Ross, Ira Z. Rothstein

Date: 13 Mar 2012

Abstract: Using the NRGR effective field theory formalism we calculate the remaining source multipole moments necessary to obtain the spin contributions to the gravitational wave amplitude to 2.5 Post-Newtonian (PN) order. We also reproduce the tail contribution to the waveform linear in spin at 2.5PN arising from the nonlinear interaction between the current quadrupole and the mass monopole.

#### Mar 16, 2012

1203.2962 (/preprints)
2012-03-16, 18:12 

## [1203.2938] Secular evolution of compact binaries near massive black holes: Gravitational wave sources and other exotica

Authors: Fabio Antonini, Hagai Perets

Date: 13 Mar 2012

Abstract: The environment near super massive black holes (SMBHs) in galactic nuclei contain a large number of stars and compact objects. A fraction of these are likely to be members of binaries. Here we discuss the binary population of stellar black holes and neutron stars near SMBHs and focus on the secular evolution of such binaries, due to the perturbation by the SMBH. Binaries with highly inclined orbits in respect to their orbit around the SMBH are strongly affected by secular Kozai processes, which periodically change their eccentricities and inclinations (Kozai-cycles). During periapsis approach, at the highest eccentricities during the Kozai-cycles, gravitational wave emission becomes highly efficient. Some binaries in this environment can inspiral and coalesce at timescales much shorter than a Hubble time and much shorter than similar binaries which do not reside near a SMBH. The close environment of SMBHs could therefore serve as catalyst for the inspiral and coalescence of binaries, and strongly affect their orbital properties. Such compact binaries would be detectable as gravitational wave (GW) sources by the next generation of GW detectors (e.g. advanced- LIGO). About 0.5% of such nuclear merging binaries will enter the LIGO observational window while on orbit that are still very eccentric (e>~0.5). The efficient gravitational wave analysis for such systems would therefore require the use of eccentric templates. We also find that binaries very close to the MBH could evolve through a complex dynamical (non-secular) evolution leading to emission of several GW pulses during only a few yrs (though these are likely to be rare). Finally, we note that the formation of close stellar binaries, X-ray binaries and their merger products could be induced by similar secular processes, combined with tidal friction rather than GW emission as in the case of compact object binaries.

#### Mar 16, 2012

1203.2938 (/preprints)
2012-03-16, 18:10 

## [1203.2150] Lunar Laser Ranging Tests of the Equivalence Principle

Authors: James G. Williams, Slava G. Turyshev, Dale Boggs

Date: 9 Mar 2012

Abstract: The Lunar Laser Ranging (LLR) experiment provides precise observations of the lunar orbit that contribute to a wide range of science investigations. In particular, time series of highly accurate measurements of the distance between the Earth and Moon provide unique information that determine whether, in accordance with the Equivalence Principle (EP), both of these celestial bodies are falling towards the Sun at the same rate, despite their different masses, compositions, and gravitational self-energies. Analyses of precise laser ranges to the Moon continue to provide increasingly stringent limits on any violation of the EP. Current LLR solutions give (-0.8 +/- 1.3) x 10ˆ{-13} for any possible inequality in the ratios of the gravitational and inertial masses for the Earth and Moon, (m_G/m_I)_E - (m_G/m_I)_M. Such an accurate result allows other tests of gravitational theories. Focusing on the tests of the EP, we discuss the existing data and data analysis techniques. The robustness of the LLR solutions is demonstrated with several different approaches to solutions. Additional high accuracy ranges and improvements in the LLR data analysis model will further advance the research of relativistic gravity in the solar system, and will continue to provide highly accurate tests of the Equivalence Principle.

#### Mar 12, 2012

1203.2150 (/preprints)
2012-03-12, 18:32 

## [1203.0317] Gravitational Wave Heating of Stars and Accretion Disks

Authors: Gongjie Li, Bence Kocsis, Abraham Loeb

Date: 1 Mar 2012

Abstract: We investigate the electromagnetic (EM) counterpart of gravitational waves (GWs) emitted by a supermassive black hole binary (SMBHB) through the viscous dissipation of the GW energy in an accretion disk and stars surrounding the SMBHB. We account for the suppression of the heating rate if the forcing period is shorter than the turnover time of the largest turbulent eddies. We find that the viscous heating luminosity in 0.1 solar mass stars can be significantly higher than their intrinsic luminosity. The relative brightening is small for accretion disks.

#### Mar 06, 2012

1203.0317 (/preprints)
2012-03-06, 11:11 

## [1202.4901] Double Compact Objects I: The Significance Of The Common Envelope On Merger Rates

Authors: Michal Dominik, Krzysztof Belczynski, Christopher Fryer, Daniel Holz, Emanuele Berti, Tomasz Bulik, Ilya Mandel, Richard O&#x27;Shaughnessy

Date: 22 Feb 2012

Abstract: The development of gravitational wave observatories (Advanced LIGO/Virgo, Einstein Telescope) is proceeding apace, and the direct detection of gravitational waves should be imminent. The last decade of observational and theoretical developments in stellar and binary evolution provides us with improvements to the predictions from populations synthesis models. Among the most important revisions in the formation and evolution of double compact objects are: updated wind mass loss rates (allowing for stellar mass black holes up to 80 Msun), a realistic treatment of the common envelope phase (that can affect merger rates by 2--3 orders of magnitude), and a qualitatively new neutron star/black hole mass distribution (consistent with the observed "mass gap"). We present a parameter study with these major physical updates included, focusing on the most important factors that set the DCO merger rates. A few of our more interesting findings are: the binding energy of the envelope and our description of natal kicks from supernovae play an important role in determining the formation and merger rate of DCOs. Also, models incorporating delayed (SASI) supernovae do not agree with the observed NS/BH "mass gap", in accordance with our previous work. And, finally, we find enhanced rates for BH-BH mergers as compared to previous estimates, with an expectation of ~100 such mergers per year in Advanced LIGO/Virgo detectors (although this rate is sensitive to factors, such as the natal kick distribution). This is the first in a series of three papers. The second paper will study the merger rates of double compact objects as a function of cosmological redshift, star formation rate, and metallicity. In the third paper we will present the detection rates for future gravitational wave observatories, using up-to-date signal waveforms and sensitivity curves. (abridged)

#### Mar 06, 2012

1202.4901 (/preprints)
2012-03-06, 11:09 

## [1202.5336] Pseudo-Newtonian Potentials for Nearly Parabolic Orbits

Authors: Christopher Wegg

Date: 23 Feb 2012

Abstract: We describe a pseudo-Newtonian potential which, to within 1% error at all angular momenta, reproduces the precession due to general relativity of particles whose specific orbital energy is small compared to cˆ2 in the Schwarzschild metric. For bound orbits the constraint of low energy is equivalent to requiring the apoapsis of a particle to be large compared to the Schwarzschild radius. Such low energy orbits are ubiquitous close to supermassive black holes in galactic nuclei, but the potential is relevant in any context containing particles on low energy orbits. Like the more complex post-Newtonian expressions, the potential correctly reproduces the precession in the far-field, but also correctly reproduces the position and magnitude of the logarithmic divergence in precession for low angular momentum orbits. An additional advantage lies in its simplicity, both in computation and implementation. We also provide two simpler, but less accurate potentials, for cases where orbits always remain at large angular momenta, or when the extra accuracy is not needed. In all of the presented cases the accuracy in precession in low energy orbits exceeds that of the well known potential of Paczynski & Wiita (1980), which has ~30% error in the precession at all angular momenta.

#### Mar 06, 2012

1202.5336 (/preprints)
2012-03-06, 11:09 

## [1202.5932] Understanding and analysing time-correlated stochastic signals in pulsar timing

Authors: Rutger van Haasteren (AEI), Yuri Levin (Monash)

Date: 27 Feb 2012

Abstract: Although it is widely understood that pulsar timing observations generally contain time-correlated stochastic signals (TCSSs; red timing noise is of this type), most data analysis techniques that have been developed make an assumption that the stochastic uncertainties in the data are uncorrelated, i.e. "white". Recent work has pointed out that this can introduce severe bias in determination of timing-model parameters, and that better analysis methods should be used. This paper presents a detailed investigation of timing-model fitting in the presence of TCSSs, and gives closed expressions for the post-fit signals in the data. This results in a Bayesian technique to obtain timing-model parameter estimates in the presence of TCSSs, as well as computationally more efficient expressions of their marginalised posterior distribution. A new method to analyse hundreds of mock dataset realisations simultaneously without significant computational overhead is presented, as well as a statistically rigorous method to check the internal consistency of the results. As a by-product of the analysis, closed expressions of the rms introduced by a stochastic background of gravitational-waves in timing-residuals are obtained. Using $T$ as the length of the dataset, and $h_c(1\rm{yr}ˆ{-1})$ as the characteristic strain, this is: $\sigma_{\rm GWB}ˆ2 = h_{c}(1\rm{yr}ˆ{-1})ˆ2 (9\sqrt[3]{2\piˆ4}\Gamma(-10/3) / 8008) \rm{yr}ˆ{-4/3} Tˆ{10/3}$.

#### Mar 06, 2012

1202.5932 (/preprints)
2012-03-06, 11:08 

## [1202.5911] Generic bounds on dipolar gravitational radiation from inspiralling compact binaries

Authors: K. G. Arun (Chennai Mathematical Instt)

Date: 27 Feb 2012

Abstract: Various alternative theories of gravity predict dipolar gravitational radiation in addition to quadrupolar radiation. We show that gravitational wave (GW) observations of inspiralling compact binaries can put interesting constraints on the strengths of the dipole modes of GW polarizations. We put forward a physically motivated gravitational waveform for dipole modes, in the Fourier domain, in terms of two parameters: one which captures the relative amplitude of the dipole mode with respect to the quadrupole mode ($\alpha$) and the other a dipole term in the phase ($\beta$). We then use this two parameter representation to discuss typical bounds on their values using GW measurements. We obtain the expected bounds on the amplitude parameter $\alpha$ and the phase parameter $\beta$ for Advanced LIGO (AdvLIGO) and Einstein Telescope (ET) noise power spectral densities using Fisher information matrix. AdvLIGO and ET may at best bound $\alpha$ to an accuracy of $\sim10ˆ{-2}$ and $\sim10ˆ{-3}$ and $\beta$ to an accuracy of $\sim10ˆ{-5}$ and $\sim10ˆ{-6}$ respectively.

#### Mar 06, 2012

1202.5911 (/preprints)
2012-03-06, 11:08 

## [1202.5699] The physical foundations for the geometric structure of relativistic theories of gravitation. From General Relativity to Extended Theories of Gravity through Ehlers-Pirani-Schild approach

Authors: S. Capozziello, M. De Laurentis, L. Fatibene, M. Francaviglia

Date: 25 Feb 2012

Abstract: We discuss in a critical way the physical foundations of geometric structure of relativistic theories of gravity by the so-called Ehlers-Pirani-Schild formalism. This approach provides a natural interpretation of the observables showing how relate them to General Relativity and to a large class of Extended Theories of Gravity. In particular we show that, in such a formalism, geodesic and causal structures of space-time can be safely disentangled allowing a correct analysis in view of observations and experiment. As specific case, we take into account the case of f(R) gravity.

#### Mar 06, 2012

1202.5699 (/preprints)
2012-03-06, 11:07 

## [1202.6311] Theoretical Aspects of the Equivalence Principle

Authors: Thibault Damour

Date: 28 Feb 2012

Abstract: We review several theoretical aspects of the Equivalence Principle (EP). We emphasize the unsatisfactory fact that the EP maintains the absolute character of the coupling constants of physics while General Relativity, and its generalizations (Kaluza-Klein,…, String Theory), suggest that all absolute structures should be replaced by dynamical entities. We discuss the EP-violation phenomenology of dilaton-like models, which is likely to be dominated by the linear superposition of two effects: a signal proportional to the nuclear Coulomb energy, related to the variation of the fine-structure constant, and a signal proportional to the surface nuclear binding energy, related to the variation of the light quark masses. We recall the various theoretical arguments (including a recently proposed anthropic argument) suggesting that the EP be violated at a small, but not unmeasurably small level. This motivates the need for improved tests of the EP. These tests are probing new territories in physics that are related to deep, and mysterious, issues in fundamental physics.

#### Mar 06, 2012

1202.6311 (/preprints)
2012-03-06, 11:07 

## [1202.6069] Testing the No-Hair Theorem with Observations in the Electromagnetic Spectrum. IV. Relativistically Broadened Iron Lines

Authors: Tim Johannsen, Dimitrios Psaltis (Arizona)

Date: 27 Feb 2012

Abstract: According to the no-hair theorem, astrophysical black holes are fully characterized by their masses and spins and are described by the Kerr metric. This theorem can be tested observationally by measuring (at least) three different multipole moments of the spacetimes of black holes. In this paper, we calculate the profiles of fluorescent iron lines emitted from the accretion flows around black holes within a framework that allows us to perform the calculation as a function of the mass and spin of a black hole as well as of a free parameter that measures potential deviations from the Kerr metric. We show that such deviations lead to line profiles that are significantly altered and exhibit a modified flux ratio of the two peaks in their characteristic double-peaked shape. We estimate the precision that near-future X-ray missions such as Astro-H and ATHENA are required to achieve in order to resolve deviations from the Kerr metric in iron line profiles and show that constraints on such deviations will be strongest for rapidly spinning black holes. More generally, we show that measuring the line profile with a precision of ~5% at a disk inclination of 30{\deg} constraints the deviation parameter to order unity irrespectively of the spin of the black hole.

#### Mar 06, 2012

1202.6069 (/preprints)
2012-03-06, 11:06 

## [1202.6063] Evolution of binary black holes in self gravitating discs: dissecting the torques

Authors: Constanze Roedig, Alberto Sesana, Massimo Dotti, Jorge Cuadra, Pau Amaro-Seoane, Francesco Haardt

Date: 27 Feb 2012

Abstract: We analyse 3D SPH simulations of the evolution of initially quasi-circular massive black hole binaries (BHBs) residing in the central hollow (cavity) of self-gravitating circumbinary discs. We perform a set of simulations adopting different thermodynamics for the gas within the cavity and for the 'numerical size' of the black holes. We study the interplay between gas accretion and gravity torques in changing the binary elements (semi-major axis and eccentricity) and its total angular momentum budget. We pay special attention to the gravity torques, by analysing their physical origin and location. We show that (i) the BHB eccentricity grows due to gravity torques from the inner edge of the disc, independently of the accretion and the adopted thermodynamics; (ii) the semi-major axis decay depends not only on the gravity torques but also on their subtle interplay with the disc-binary angular momentum transfer due to accretion; (iii) the spectral structure of the gravity torques is predominately caused by disc edge overdensities and spiral arms developing in the body of the disc; (iv) the net gravity torque changes sign across the BHB corotation radius: gas inside this radius exerts a net positive torque, while streams located outside this radius (but within the cavity) exert a net negative torque. The relative importance of the two might depend on the thermodynamical properties of the instreaming gas and is crucial in assessing the disc--binary angular momentum transfer; (v) the net torque manifests as a purely kinematic effect as it stems from the low density cavity, where the material flows in and out in highly eccentric orbits. Thus both accretion onto the black holes and the interaction with gas streams inside the cavity must be taken into account to assess the fate of the binary.

#### Mar 06, 2012

1202.6063 (/preprints)
2012-03-06, 11:05 

## [1203.0401] Prospects for transient gravitational waves at r-mode frequencies associated with pulsar glitches

Authors: I. Santiago-Prieto, I. S. Heng, D. I. Jones, J. Clark

Date: 2 Mar 2012

Abstract: Glitches in pulsars are likely to trigger oscillation modes in the fluid interior of neutron stars. We examined these oscillations specifically at r-mode frequencies. The excited r-modes will emit gravitational waves and can have long damping time scales O(minutes - days). We use simple estimates of how much energy the glitch might put into the r-mode and assess the detectability of the emitted gravitational waves with future interferometers.

#### Mar 06, 2012

1203.0401 (/preprints)
2012-03-06, 11:03 

## [1203.0398] Effective action approach to cosmological perturbations in dark energy and modified gravity

Authors: Richard A. Battye, Jonathan A. Pearson

Date: 2 Mar 2012

Abstract: In light of upcoming observations modelling perturbations in dark en- ergy and modified gravity models has become an important topic of research. We develop an effective action to construct the components of the perturbed dark energy momentum tensor which appears in the perturbed generalized gravitational field equations, {\delta}G_{\mu\nu} = 8{\pi}G{\delta}T_{\mu\nu} + {\delta}U_{\mu\nu} for linearized perturbations. Our method does not require knowledge of the Lagrangian density of the dark sector to be provided, only its field content. The method is based on the fact that it is only necessary to specify the perturbed Lagrangian to quadratic order and couples this with the assumption of global statistical isotropy of spatial sections to show that the model can be specified completely in terms of a finite number of background dependent functions. We present our formalism in a coordinate independent fashion and provide explicit formulae for the perturbed conservation equation and the components of {\delta}U_{\mu\nu} for two explicit generic examples: (i) the dark sector does not contain extra fields, L = L(g_{\mu\nu}) and (ii) the dark sector contains a scalar field and its first derivative L = L(g_{\mu\nu}, {\phi}, \nabla_{\mu}{\phi}). We discuss how the formalism can be applied to modified gravity models containing derivatives of the metric, curvature tensors, higher derivatives of the scalar fields and vector fields.

#### Mar 06, 2012

1203.0398 (/preprints)
2012-03-06, 11:03 

## [1203.1010] Periodic Orbits and Escapes in Dynamical Systems

Authors: George Contopoulos, Mirella Harsoula, Georgios Lukes-Gerakopoulos

Date: 5 Mar 2012

Abstract: We study the periodic orbits and the escapes in two different dynamical systems, namely (1) a classical system of two coupled oscillators, and (2) the Manko-Novikov metric (1992) which is a perturbation of the Kerr metric (a general relativistic system). We find their simple periodic orbits, their characteristics and their stability. Then we find their ordered and chaotic domains. As the energy goes beyond the escape energy, most chaotic orbits escape. In the first case we consider escapes to infinity, while in the second case we emphasize escapes to the central "bumpy" black hole. When the energy reaches its escape value a particular family of periodic orbits reaches an infinite period and then the family disappears (the orbit escapes). As this family approaches termination it undergoes an infinity of equal period and double period bifurcations at transitions from stability to instability and vice versa. The bifurcating families continue to exist beyond the escape energy. We study the forms of the phase space for various energies, and the statistics of the chaotic and escaping orbits. The proportion of these orbits increases abruptly as the energy goes beyond the escape energy.

#### Mar 05, 2012

1203.1010 (/preprints)
2012-03-05, 18:12 

## [1202.4951] Advance of Planetary Perihelion in Post-Newtonian Gravity

Authors: Alexis Larranaga, Luis Cabarique

Date: 22 Feb 2012

Abstract: We present an elementary derivation of the planetary advance of the perihelion for a general spherically symmetric line element in the post- newtonian approximation.

#### Feb 23, 2012

1202.4951 (/preprints)
2012-02-23, 08:46 

## [1202.4202] Two New Tidally Distorted White Dwarfs

Authors: J. J. Hermes, Mukremin Kilic, Warren R. Brown, M. H. Montgomery, D. E. Winget

Date: 20 Feb 2012

Abstract: We identify two new tidally distorted white dwarfs (WDs), SDSS J174140.49+652638.7 and J211921.96-001825.8 (hereafter J1741 and J2119). Both stars are extremely low mass (ELM, < 0.2 Msun) WDs in short-period, detached binary systems. High-speed photometric observations obtained at the McDonald Observatory reveal ellipsoidal variations and Doppler beaming in both systems; J1741, with a minimum companion mass of 1.1 Msun, has one of the strongest Doppler beaming signals ever observed in a binary system (0.59 \pm 0.06% amplitude). We use the observed ellipsoidal variations to constrain the radius of each WD. For J1741, the star's radius must exceed 0.074 Rsun. For J2119, the radius exceeds 0.10 Rsun. These indirect radius measurements are comparable to the radius measurements for the bloated WD companions to A-stars found by the Kepler spacecraft, and they constitute some of the largest radii inferred for any WD. Surprisingly, J1741 also appears to show a 0.23 \pm 0.06% reflection effect, and we discuss possible sources for this excess heating. Both J1741 and J2119 are strong gravitational wave sources, and the time-of-minimum of the ellipsoidal variations can be used to detect the orbital period decay. This may be possible on a timescale of a decade or less.

#### Feb 23, 2012

1202.4202 (/preprints)
2012-02-23, 08:46 

## [1202.4750] Multipole expansion at the level of the action

Authors: Andreas Ross

Date: 21 Feb 2012

Abstract: Sources of long wavelength radiation are naturally described by an effective field theory (EFT) which takes the form of a multipole expansion. Its action is given by a derivative expansion where higher order terms are suppressed by powers of the ratio of the size of the source over the wavelength. In order to determine the Wilson coefficients of the EFT, i.e. the multipole moments, one needs the mapping between a linear source term action and the multipole expansion form of the action of the EFT. In this paper we perform the multipole expansion to all orders by Taylor expanding the field in the source term and then decomposing the action into symmetric trace free tensors which form irreducible representations of the rotation group. We work at the level of the action, and we obtain the action to all orders in the multipole expansion and the exact expressions for the multipole moments for a scalar field, electromagnetism and linearized gravity. Our results for the latter two cases are manifestly gauge invariant. We also give expressions for the energy flux and the (gauge dependent) radiation field to all orders in the multipole expansion. The results for linearized gravity are a component of the EFT framework NRGR and will greatly simplify future calculations of gravitational wave observables in the radiation sector of NRGR.

#### Feb 23, 2012

1202.4750 (/preprints)
2012-02-23, 08:46 

## [1202.4688] Mergers and ejections of black holes in globular clusters

Authors: Sverre Aarseth (IoA, Cambridge)

Date: 21 Feb 2012

Abstract: We report on results of fully consistent N-body simulations of globular cluster models with N = 100 000 members containing neutron stars and black holes. Using the improved ‘algorithmic regularization’ method of Hellstrom and Mikkola for compact subsystems, the new code NBODY7 enables for the first time general relativistic coalescence to be achieved for post-Newtonian terms and realistic parameters. Following an early stage of mass segregation, a few black holes form a small dense core which usually leads to the formation of one dominant binary. The subsequent evolution by dynamical shrinkage involves the competing processes of ejection and mergers by radiation energy loss. Unless the binary is ejected, long-lived triple systems often exhibit Kozai cycles with extremely high inner eccentricity (e > 0.999) which may terminate in coalescence at a few Schwarzschild radii. A characteristic feature is that ordinary stars as well as black holes and even BH binaries are ejected with high velocities. On the basis of the models studied so far, the results suggest a limited growth of a few remaining stellar mass black holes in globular clusters.

#### Feb 23, 2012

1202.4688 (/preprints)
2012-02-23, 08:46 

## [1202.4031] Prospects for early localization of gravitational-wave signals from compact binary coalescences with advanced detectors

Authors: Alessandro Manzotti, Alexander Dietz

Date: 17 Feb 2012

Abstract: A leading candidate source of detectable gravitational waves is the inspiral and merger of pairs of stellar-mass compact objects. The advanced LIGO and advanced Virgo detectors will allow scientists to detect inspiral signals from more massive systems and at earlier times in the detector band, than with first generation detectors. The signal from a coalescence of two neutron stars is expected to stay in the sensitive band of advanced detectors for several minutes, thus allowing detection before the final coalescence of the system. In this work, the prospects of detecting inspiral signals prior to coalescence, and the possibility to derive a suitable sky area for source locations are investigated. As a large fraction of the signal is accumulated in the last ~10 seconds prior to coalescence, bandwidth and timing accuracy are largely accrued in the very last moments prior to coalescence. We use Monte Carlo techniques to estimate the accuracy of sky localization through networks of ground-based interferometers such as aLIGO and aVirgo. With the addition of the Japanese KAGRA detector, it is shown that the detection and triangulation before coalescence may be feasible.

#### Feb 23, 2012

1202.4031 (/preprints)
2012-02-23, 08:45 

## [1202.3565] Effective action approach to higher-order relativistic tidal interactions in binary systems and their effective one body description

Authors: Donato Bini, Thibault Damour, Guillaume Faye

Date: 16 Feb 2012

Abstract: The gravitational-wave signal from inspiralling neutron-star--neutron-star (or black-hole--neutron-star) binaries will be influenced by tidal coupling in the system. An important science goal in the gravitational-wave detection of these systems is to obtain information about the equation of state of neutron star matter via the measurement of the tidal polarizability parameters of neutron stars. To extract this piece of information will require to have accurate analytical descriptions of both the motion and the radiation of tidally interacting binaries. We improve the analytical description of the late inspiral dynamics by computing the next-to-next-to-leading order relativistic correction to the tidal interaction energy. Our calculation is based on an effective-action approach to tidal interactions, and on its transcription within the effective-one-body formalism. We find that second-order relativistic effects (quadratic in the relativistic gravitational potential $u=G(m_1 +m_2)/(cˆ2 r)$) significantly increase the effective tidal polarizability of neutron stars by a distance-dependent amplification factor of the form $1 + \alpha_1 \, u + \alpha_2 \, uˆ2 +…$ where, say for an equal-mass binary, $\alpha_1=5/4=1.25$ (as previously known) and $\alpha_2=85/14\simeq6.07143$ (as determined here for the first time). We argue that higher-order relativistic effects will lead to further amplification, and we suggest a Padé-type way of resumming them. We recommend to test our results by comparing resolution-extrapolated numerical simulations of inspiralling-binary neutron stars to their effective one body description.

#### Feb 23, 2012

1202.3565 (/preprints)
2012-02-23, 08:45 

## [1202.3512] Gravitational wave observations of galactic intermediate-mass black hole binaries with DECIGO Path Finder

Authors: Kent Yagi

Date: 16 Feb 2012

Abstract: DECIGO Path Finder (DPF) is a space-borne gravitational wave (GW) detector with sensitivity in the frequency band 0.1--100Hz. As a first step mission to DECIGO, it is aiming for launching in 2016--2017. Although its main objective is to demonstrate technology for GW observation in space, DPF still has a chance of detecting GW signals and performing astrophysical observations. With an observable range up to 50 kpc, its main targets are GW signals from galactic intermediate mass black hole (IMBH) binaries. By using inspiral-merger-ringdown phenomenological waveforms, we perform both pattern-averaged analysis and Monte Carlo simulations including the effect of detector motion to find that the masses and (effective) spins of the IMBHs could be determined with errors of a few percent, should the signals be detected. Since GW signals from IMBH binaries with masses above $10ˆ4 M_\odot$ cannot be detected by ground-based detectors, these objects can be unique sources for DPF. If the inspiral signal of a $10ˆ3M_\odot$ IMBH binary is detected with DPF, it can give alert to the ringdown signal for the ground-based detectors $10ˆ2$--$10ˆ3$s before coalescence. We also estimate the possible bound on the graviton Compton wavelength from a possible IMBH binary in $\omega$ Centauri. We obtain a slightly weaker constraint than the solar system experiment and an about 2 orders of magnitude stronger constraint than the one from binary pulsar tests. Unfortunately, the detection rate of IMBH binaries is rather small.

#### Feb 23, 2012

1202.3512 (/preprints)
2012-02-23, 08:45 

## [1202.3990] A Bayesian Approach to Calibrating Period-Luminosity Relations of RR Lyrae Stars in the Mid-Infrared

Authors: Christopher R. Klein, Joseph W. Richards, Nathaniel R. Butler, Joshua S. Bloom

Date: 17 Feb 2012

Abstract: A Bayesian approach to calibrating period-luminosity (PL) relations has substantial benefits over generic least-squares fits. In particular, the Bayesian approach takes into account the full prior distribution of the model parameters, such as the a priori distances, and refits these parameters as part of the process of settling on the most highly-constrained final fit. Additionally, the Bayesian approach can naturally ingest data from multiple wavebands and simultaneously fit the parameters of PL relations for each waveband in a procedure that constrains the parameter posterior distributions so as to minimize the scatter of the final fits appropriately in all wavebands. Here we describe the generalized approach to Bayesian model fitting and then specialize to a detailed description of applying Bayesian linear model fitting to the mid-infrared PL relations of RR Lyrae variable stars. For this example application we quantify the improvement afforded by using a Bayesian model fit. We also compare distances previously predicted in our example application to recently published parallax distances measured with the Hubble Space Telescope and find their agreement to be a vindication of our methodology. Our intent with this article is to spread awareness of the benefits and applicability of this Bayesian approach and encourage future PL relation investigations to consider employing this powerful analysis method.

#### Feb 23, 2012

1202.3990 (/preprints)
2012-02-23, 08:45 

## [1202.3595] Detecting Cosmic Gravitational-wave Background from Super-heavy Cosmic Strings with LISA

Authors: Alf Tang, Timothy J. Sumner

Date: 16 Feb 2012

Abstract: Although cosmic string scenario for galaxy formation is disfavored by CMB data, it is of great interest in the generation of cosmic gravitational-wave background. This research aims to develop an algorithm to extract cosmic gravitational-wave background produced by cosmic strings from the LISA data stream, and apply the algorithm to the simulated data stream containing the background produced by cosmic strings with various strength to study the detection threshold for this source. For 1-yr observation, It is found that the detection threshold of G{\mu} is 3.12 \times 10ˆ-16 in the standard scenario. In the case that p and {\epsilon} are adjustable, the detectable region in parameter space is defined by (G{\mu})ˆ2/3 {\epsilon}ˆ-1/3 / p> 4.6 \times 10-11.

#### Feb 23, 2012

1202.3595 (/preprints)
2012-02-23, 08:45 

## [1202.4893] Black hole perturbation in the most general scalar-tensor theory with second-order field equations I: the odd-parity sector

Authors: Tsutomu Kobayashi, Hayato Motohashi, Teruaki Suyama

Date: 22 Feb 2012

Abstract: We perform a fully relativistic analysis of odd-type linear perturbations around a static and spherically symmetric solution in the most general scalar-tensor theory with second-order field equations. It is shown that, as in the case of general relativity, the quadratic action for the perturbations reduces to the one having only a single dynamical variable, from which concise formulas for no-ghost and no-gradient instability conditions are derived. Our result is applicable to all the theories of gravity with an extra scalar degree of freedom. We demonstrate how the generic formulas can be applied to some particular examples such as the Brans-Dicke theory, $f(R)$ models, and Galileon gravity.

#### Feb 23, 2012

1202.4893 (/preprints)
2012-02-23, 08:39 

## [1202.2179] The Swift short gamma-ray burst rate density: implications for binary neutron star merger rates

Authors: David Coward, Eric Howell, Tsvi Piran, Giulia Stratta, Marica Branchesi, Omer Bromberg, Bruce Gendre, Ronald Burman, Dafne Guetta

Date: 10 Feb 2012

Abstract: Short gamma-ray bursts (SGRBs) observed by {\it Swift} are potentially revealing the first insight into cataclysmic compact object mergers. To ultimately acquire a fundamental understanding of these events requires pan-spectral observations and knowledge of their spatial distribution to differentiate between proposed progenitor populations. Presently (late 2011) there are only some 30% of SGRBs with reasonably firm redshifts, and this sample is highly biased by the limited sensitivity of {\it Swift} to detect SGRBs. We account for the dominant biases to calculate a realistic SGRB rate density out to $z\approx0.5$ using the {\it Swift} sample of peak fluxes, redshifts, and those SGRBs with a beaming angle constraint from X-ray/optical observations. We find an SGRB lower rate density of $7.1ˆ{+4.9}_{-3.2}$ $\mathrm{Gpc}ˆ{-3}\mathrm{yr}ˆ{-1}$ (assuming isotropic emission), and a beaming corrected upper limit of $1200ˆ{+840}_{-550}$ $\mathrm{Gpc}ˆ{-3}\mathrm{yr}ˆ{-1}$. Assuming a significant fraction of binary neutron star mergers produce SGRBs, we calculate lower and upper detection rate limits of $(1-200)$ yr$ˆ{-1}$ by an ALIGO and Virgo coincidence search. Our detection rate is similar to the lower and realistic rates inferred from extrapolations using Galactic pulsar observations and population synthesis.

#### Feb 12, 2012

1202.2179 (/preprints)
2012-02-12, 23:17 

## [1202.1986] Perturbations in Massive Gravity Cosmology

Authors: Marco Crisostomi, Denis Comelli, Luigi Pilo

Date: 9 Feb 2012

Abstract: We study cosmological perturbations for a ghost free massive gravity theory formulated with a dynamical extra metric that is needed to massive deform GR. In this formulation FRW background solutions fall in two branches. In the dynamics of perturbations around the first branch solutions, no extra degree of freedom with respect to GR ispresent at linearized level, likewise what is found in the Stuckelberg formulation of massive gravity where the extra metric isflat and non dynamical. In the first branch, perturbations are probably strongly coupled. On the contrary, for perturbations around the second branch solutions all expected degrees of freedom propagate. While tensor and vector perturbations of the physical metric that couples with matter follow closely the ones of GR, scalars develop an exponential Jeans-like instability on sub-horizon scales. On the other hand, around a de Sitter background there is no instability. We argue that one could get rid of the instabilities by introducing a mirror dark matter sector minimally coupled to only the second metric.

#### Feb 09, 2012

1202.1986 (/preprints)
2012-02-09, 20:42 

## [1202.1977] Recoiling black holes: electromagnetic signatures, candidates, and astrophysical implications

Authors: S. Komossa (TUM/ExCU/IPP)

Date: 9 Feb 2012

Abstract: Supermassive black holes (SMBHs) may not always reside right at the centers of their host galaxies. This is a prediction of numerical relativity simulations, which imply that the newly formed single SMBH, after binary coalescence in a galaxy merger, can receive kick velocities up to several 1000 km/s due to anisotropic emission of gravitational waves. Long-lived oscillations of the SMBHs in galaxy cores, and in rare cases even SMBH ejections from their host galaxies, are the consequence. Observationally, accreting recoiling SMBHs would appear as quasars spatially and/or kinematically off-set from their host galaxies. The presence of the "kicks" has a wide range of astrophysical implications which only now are beginning to be explored, including consequences for black hole and galaxy assembly at the epoch of structure formation, black hole feeding, and unified models of Active Galactic Nuclei (AGN). Here, we review the observational signatures of recoiling SMBHs and the properties of the first candidates which have emerged, including follow-up studies of the candidate recoiling SMBH of SDSSJ092712.65+294344.0.

#### Feb 09, 2012

1202.1977 (/preprints)
2012-02-09, 20:42 

## [1202.0839] Low-frequency gravitational-wave science with eLISA/NGO

Authors: Pau Amaro-Seoane, Sofiane Aoudia, Stanislav Babak, Pierre Binetruy, Emanuele Berti, Alejandro Bohe, Chiara Caprini, Monica Colpi, Neil J. Cornish, Karsten Danzmann, Jean-Francois Dufaux, Jonathan Gair, Oliver Jennrich, Philippe Jetzer, Antoine Klein, Ryan N. Lang, Alberto Lobo, Tyson Littenberg, Sean T. McWilliams, Gijs Nelemans, Antoine Petiteau, Edward K. Porter, Bernard F. Schutz, Alberto Sesana, Robin Stebbins, Tim Sumner, Michele Vallisneri, Stefano Vitale, Marta Volonteri, Henry Ward

Date: 3 Feb 2012

Abstract: We review the expected science performance of the New Gravitational-Wave Observatory (NGO, a.k.a. eLISA), a mission under study by the European Space Agency for launch in the early 2020s. eLISA will survey the low-frequency gravitational-wave sky (from 0.1 mHz to 1 Hz), detecting and characterizing a broad variety of systems and events throughout the Universe, including the coalescences of massive black holes brought together by galaxy mergers; the inspirals of stellar-mass black holes and compact stars into central galactic black holes; several millions of ultracompact binaries, both detached and mass transferring, in the Galaxy; and possibly unforeseen sources such as the relic gravitational-wave radiation from the early Universe. eLISA's high signal-to-noise measurements will provide new insight into the structure and history of the Universe, and they will test general relativity in its strong-field dynamical regime.

#### Feb 07, 2012

1202.0839 (/preprints)
2012-02-07, 12:01 

## [1202.0790] A prototype effective-one-body model for non-precessing spinning inspiral-merger-ringdown waveforms

Authors: Andrea Taracchini, Yi Pan, Alessandra Buonanno, Enrico Barausse, Michael Boyle, Tony Chu, Geoffrey Lovelace, Harald P. Pfeiffer, Mark A. Scheel

Date: 3 Feb 2012

Abstract: We first use five non-spinning and two mildly spinning (chi_i \simeq -0.44, +0.44) numerical-relativity waveforms of black-hole binaries and calibrate an effective-one-body (EOB) model for non-precessing spinning binaries, notably its dynamics and the dominant (2,2) gravitational-wave mode. Then, we combine the above results with recent outcomes of small-mass-ratio simulations produced by the Teukolsky equation and build a prototype EOB model for detection purposes, which is capable of generating inspiral-merger-ringdown waveforms for non-precessing spinning black-hole binaries with any mass ratio and individual black-hole spins -1 \leq chi_i \lesssim 0.7. We compare the prototype EOB model to two equal-mass highly spinning numerical-relativity waveforms of black holes with spins chi_i = -0.95, +0.97, which were not available at the time the EOB model was calibrated. In the case of Advanced LIGO we find that the mismatch between prototype-EOB and numerical-relativity waveforms is always smaller than 0.003 for total mass 20-200 M_\odot, the mismatch being computed by maximizing only over the initial phase and time. To successfully generate merger waveforms for individual black-hole spins chi_i \gtrsim 0.7, the prototype-EOB model needs to be improved by (i) better modeling the plunge dynamics and (ii) including higher-order PN spin terms in the gravitational-wave modes and radiation-reaction force.

#### Feb 05, 2012

1202.0790 (/preprints)
2012-02-05, 22:35 

## [1202.0808] Practical Methods for Continuous Gravitational Wave Detection using Pulsar Timing Data

Authors: J. A. Ellis, F. A. Jenet, M. A. McLaughlin

Date: 3 Feb 2012

Abstract: Gravitational Waves (GWs) are tiny ripples in the fabric of space-time predicted by Einstein's General Relativity. Pulsar timing arrays (PTAs) are well poised to detect low frequency ($10ˆ{-9}$ -- $10ˆ{-7}$ Hz) GWs in the near future. There has been a significant amount of research into the detection of a stochastic background of GWs from supermassive black hole binaries (SMBHBs). Recent work has shown that single continuous sources standing out above the background may be detectable by PTAs operating at a sensitivity sufficient to detect the stochastic background. The most likely sources of continuous GWs in the pulsar timing frequency band are extremely massive and/or nearby SMBHBs. In this paper we present detection strategies including various forms of matched filtering and power spectral summing. We determine the efficacy and computational cost of such strategies. It is shown that it is computationally infeasible to use an optimal matched filter including the poorly constrained pulsar distances with a grid based method. We show that an Earth-term-matched filter constructed using only the correlated signal terms is both computationally viable and highly sensitive to GW signals. This technique is only a factor of two less sensitive than the computationally unrealizable optimal matched filter and a factor of two more sensitive than a power spectral summing technique. We further show that a pairwise matched filter, taking the pulsar distances into account is comparable to the optimal matched filter for the single template case and comparable to the Earth-term-matched filter for many search templates. Finally, using simulated data optimal quality, we place a theoretical minimum detectable strain amplitude of $h>2\times 10ˆ{-15}$ from continuous GWs at frequencies on the order $\sim1/T_{\rm obs}$.

#### Feb 05, 2012

1202.0808 (/preprints)
2012-02-05, 22:35 

## [1202.0804] Compact object coalescence rate estimation from short gamma-ray burst observations

Authors: Carlo Enrico Petrillo, Alexander Dietz

Date: 3 Feb 2012

Abstract: Recent observational and theoretical work increase the confidence that short-duration gamma-ray bursts are created by the coalescence of compact objects, like neutron stars and/or black holes. From the observation of short-duration gamma-ray bursts with know distances it is possible to infer their rate in the local universe, and draw conclusions for the rate of compact binary coalescences. Although the sample of such events with reliable redshift measurements is very small, we try to model the distribution with a luminosity function and a rate function. The analysis performed with a sample of 15 short gamma-ray bursts yields a range for the merger rate of 75 to 660 Gpc$ˆ{-3}$yr$ˆ{-1}$, with a median rate of 180 Gpc$ˆ{-3}$yr$ˆ{-1}$. This result is in general agreement with similar investigations using gamma-ray burst observations. Furthermore, we estimate the number of coincident observations of gravitational wave signals with short gamma-ray bursts in the advanced detector era. Assuming each short gamma-ray burst is created by a double neutron star merger, the expected rate of coincident observations is 0.1 to 1.1 per year, when assuming each short gamma-ray burst is created by a merger of a neutron star and a black hole, this rate becomes 0.4 to 4.0 per year.

#### Feb 05, 2012

1202.0804 (/preprints)
2012-02-05, 22:35 

## [1202.0394] Black holes and stellar structures in f(R)-gravity

Authors: M. De Laurentis, S. Capozziello

Date: 2 Feb 2012

Abstract: We review black hole solutions and self-gravitating structures in f(R)-gravity.

#### Feb 02, 2012

1202.0394 (/preprints)
2012-02-02, 18:22 

## [1201.5319] The NINJA-2 catalog of hybrid post-Newtonian/numerical-relativity waveforms for non-precessing black-hole binaries

Authors: P. Ajith, Michael Boyle, Duncan A. Brown, Bernd Br&#xfc;gmann, Luisa T. Buchman, Laura Cadonati, Manuela Campanelli, Tony Chu, Zachariah B. Etienne, Stephen Fairhurst, Mark Hannam, James Healy, Ian Hinder, Sascha Husa, Lawrence E. Kidder, Badri Krishnan, Pablo Laguna, Yuk Tung Liu, Lionel London, Carlos O. Lousto, Geoffrey Lovelace, Ilana MacDonald, Pedro Marronetti, Satya Mohapatra, Philipp M&#xf6;sta, Doreen M&#xfc;ller, Bruno C. Mundim, Hiroyuki Nakano, Frank Ohme, Vasileios Paschalidis, Larne Pekowsky, Denis Pollney, Harald P. Pfeiffer, Marcelo Ponce, Michael P&#xfc;rrer, George Reifenberger, Christian Reisswig, Luc&#xed;a Santamar&#xed;a, Mark A. Scheel, Stuart L. Shapiro, Deirdre Shoemaker, Carlos F. Sopuerta, Ulrich Sperhake, B&#xe9;la Szil&#xe1;gyi, Nicholas W. Taylor, Wolfgang Tichy, Petr Tsatsin, Yosef Zlochower

Date: 25 Jan 2012

Abstract: The Numerical INJection Analysis (NINJA) project is a collaborative effort between members of the numerical relativity and gravitational wave data analysis communities. The purpose of NINJA is to study the sensitivity of existing gravitational-wave search and parameter-estimation algorithms using numerically generated waveforms, and to foster closer collaboration between the numerical relativity and data analysis communities. The first NINJA project used only a small number of injections of short numerical-relativity waveforms, which limited its ability to draw quantitative conclusions. The goal of the NINJA-2 project is to overcome these limitations with long post-Newtonian - numerical relativity hybrid waveforms, large numbers of injections, and the use of real detector data. We report on the submission requirements for the NINJA-2 project and the construction of the waveform catalog. Eight numerical relativity groups have contributed 63 hybrid waveforms consisting of a numerical portion modelling the late inspiral, merger, and ringdown stitched to a post-Newtonian portion modelling the early inspiral. We summarize the techniques used by each group in constructing their submissions. We also report on the procedures used to validate these submissions, including examination in the time and frequency domains and comparisons of waveforms from different groups against each other. These procedures have so far considered only the $(\ell,m)=(2,2)$ mode. Based on these studies we judge that the hybrid waveforms are suitable for NINJA-2 studies. We note some of the plans for these investigations.

#### Feb 02, 2012

1201.5319 (/preprints)
2012-02-02, 16:16 

## [1201.5244] An F-statistic based multi-detector veto for detector artifacts in continuous-wave gravitational wave data

Authors: David Keitel, Reinhard Prix, Maria Alessandra Papa, Maham Siddiqi

Date: 25 Jan 2012

Abstract: Continuous gravitational waves (CW) are expected from spinning neutron stars with non-axisymmetric deformations. A network of interferometric detectors (LIGO, Virgo and GEO600) is looking for these signals. They are predicted to be very weak and retrievable only by integration over long observation times. One of the standard methods of CW data analysis is the multi-detector F-statistic. In a typical search, the F-statistic is computed over a range in frequency, spin-down and sky position, and the candidates with highest F values are kept for further analysis. However, this detection statistic is susceptible to a class of noise artifacts, strong monochromatic lines in a single detector. By assuming an extended noise model - standard Gaussian noise plus single-detector lines - we can use a Bayesian odds ratio to derive a generalized detection statistic, the line veto (LV-) statistic. In the absence of lines, it behaves similarly to the F-statistic, but it is more robust against line artifacts. In the past, ad-hoc post-processing vetoes have been implemented in searches to remove these artifacts. Here we provide a systematic framework to develop and benchmark this class of vetoes. We present our results from testing this LV-statistic on simulated data.

#### Feb 02, 2012

1201.5244 (/preprints)
2012-02-02, 16:15 

## [1201.5599] Performance of an externally triggered gravitational-wave burst search

Authors: Michal Was, Patrick J. Sutton, Gareth Jones, Isabel Leonor

Date: 26 Jan 2012

Abstract: We present the performance of searches for gravitational wave bursts associated with external astrophysical triggers as a function of the search sky region. We discuss both the case of Gaussian noise and real noise of gravitational wave detectors for arbitrary detector networks. We demonstrate the ability to reach Gaussian limited sensitivity in real non-Gaussian data, and show the conditions required to attain it. We find that a single sky position search is ~20% more sensitive than an all-sky search of the same data.

#### Feb 02, 2012

1201.5599 (/preprints)
2012-02-02, 16:15 

## [1201.5888] The evolution of massive black holes and their spins in their galactic hosts

Authors: Enrico Barausse

Date: 27 Jan 2012

Abstract: [Abridged] […] In this paper, we study the mass and spin evolution of massive black holes within a semianalytical galaxy-formation model that follows the evolution of dark-matter halos along merger trees, as well as that of the baryonic components (hot gas, stellar and gaseous bulges, and stellar and gaseous galactic disks). This allows us to study the mass and spin evolution of massive black holes in a self-consistent way, by taking into account the effect of the gas present in galactic nuclei both during the accretion phases and during mergers. Also, we present predictions, as a function of redshift, for the fraction of gas-rich black-hole mergers -- in which the spins prior to the merger are aligned due to the gravito-magnetic torques exerted by the circumbinary disk -- as opposed to gas-poor mergers, in which the orientation of the spins before the merger is roughly isotropic. These predictions may be tested by LISA or similar spaced-based gravitational-wave detectors such as eLISA/NGO or SGO.

#### Feb 02, 2012

1201.5888 (/preprints)
2012-02-02, 16:14 

## [1201.5715] Approximate Waveforms for Extreme-Mass-Ratio Inspirals: The Chimera Scheme

Authors: Carlos F. Sopuerta, Nicolas Yunes

Date: 27 Jan 2012

Abstract: We describe a new kludge scheme to model the dynamics of generic extreme-mass-ratio inspirals (EMRIs; stellar compact objects spiraling into a spinning supermassive black hole) and their gravitational-wave emission. The Chimera scheme is a hybrid method that combines tools from different approximation techniques in General Relativity: (i) A multipolar, post-Minkowskian expansion for the far-zone metric perturbation (the gravitational waveforms) and for the local prescription of the self-force; (ii) a post-Newtonian expansion for the computation of the multipole moments in terms of the trajectories; and (iii) a BH perturbation theory expansion when treating the trajectories as a sequence of self-adjusting Kerr geodesics. The EMRI trajectory is made out of Kerr geodesic fragments joined via the method of osculating elements as dictated by the multipolar post-Minkowskian radiation-reaction prescription. We implemented the proper coordinate mapping between Boyer-Lindquist coordinates, associated with the Kerr geodesics, and harmonic coordinates, associated with the multipolar post-Minkowskian decomposition. The Chimera scheme is thus a combination of approximations that can be used to model generic inspirals of systems with extreme to intermediate mass ratios, and hence, it can provide valuable information for future space-based gravitational-wave observatories, like LISA, and even for advanced ground detectors. The local character in time of our multipolar post-Minkowskian self-force makes this scheme amenable to study the possible appearance of transient resonances in generic inspirals.

#### Feb 02, 2012

1201.5715 (/preprints)
2012-02-02, 16:13 

## [1201.5656] Comparison of Atom Interferometers and Light Interferometers as Space-Based Gravitational Wave Detectors

Authors: John G. Baker, James Ira Thorpe

Date: 26 Jan 2012

Abstract: We consider a class of proposed gravitational wave detectors based on multiple atomic interferometers separated by large baselines and referenced by common laser systems. We compute the sensitivity limits of these detectors due to intrinsic phase noise of the light sources, non-inertial motion of the light sources, and atomic shot noise and compare them to sensitivity limits for traditional light interferometers. We find that atom interferometers and light interferometers are limited in a nearly identical way by intrinsic phase noise and that both require similar mitigation strategies (e.g. multiple arm instruments) to reach interesting sensitivities. The sensitivity limit from motion of the light sources is slightly different and favors the atom interferometers in the low-frequency limit, although the limit in both cases is severe.

#### Feb 02, 2012

1201.5656 (/preprints)
2012-02-02, 16:13 

## [1201.5999] Search for Gravitational Waves from Intermediate Mass Binary Black Holes

Date: 28 Jan 2012

Abstract: We present the results of a weakly modeled burst search for gravitational waves from mergers of non-spinning intermediate mass black holes (IMBH) in the total mass range 100--450 solar masses and with the component mass ratios between 1:1 and 4:1. The search was conducted on data collected by the LIGO and Virgo detectors between November of 2005 and October of 2007. No plausible signals were observed by the search which constrains the astrophysical rates of the IMBH mergers as a function of the component masses. In the most efficiently detected bin centered on 88+88 solar masses, for non-spinning sources, the rate density upper limit is 0.13 per Mpcˆ3 per Myr at the 90% confidence level.

#### Feb 02, 2012

1201.5999 (/preprints)
2012-02-02, 16:11 

## [1201.5089] Second-order gravitational self-force

Date: 24 Jan 2012

Abstract: Using a rigorous method of matched asymptotic expansions, I derive the equation of motion of a small, compact body in an external vacuum spacetime through second order in the body's mass (neglecting effects of internal structure). The motion is found to be geodesic in a certain locally defined regular geometry satisfying Einstein's equation at second order. I provide a practical scheme for numerically obtaining both the metric of that regular geometry and the complete second-order metric perturbation produced by the body.

#### Jan 25, 2012

1201.5089 (/preprints)
2012-01-25, 10:34 

## [1201.4873] Magnetically-levitating disks around supermassive black holes

Authors: Evghenii Gaburov, Anders Johansen, Yuri Levin

Date: 23 Jan 2012

Abstract: In this paper we report on the formation of magnetically-levitating accretion disks around supermassive black holes. The structure of these disks is calculated by numerically modelling tidal disruption of magnetized interstellar gas clouds. We find that the resulting disks are entirely supported by the pressure of the magnetic fields against the component of gravitational force directed perpendicular to the disks. The magnetic field shows ordered large-scale geometry that remains stable for the duration of our numerical experiments extending over 10% of the disk lifetime. Strong magnetic pressure allows high accretion and inhibits disk fragmentation. This in combination with the repeated feeding of manetized molecular clouds to a supermassive black hole yields a possible solution to the long-standing puzzle of black hole growth in the centres of galaxies.

#### Jan 25, 2012

1201.4873 (/preprints)
2012-01-25, 10:34 

## [1201.5041] Radioscience simulations in General Relativity and in alternative theories of gravity

Authors: A. Hees, B. Lamine, S. Reynaud, M.-T. Jaekel, C. Le Poncin-Lafitte, V. Lainey, A. F&#xfc;zfa, J.-M. Courty, V. Dehant, P. Wolf

Date: 24 Jan 2012

Abstract: In this paper, we focus on the possibility to test General Relativity in the Solar System with radioscience measurements. To this aim, we present a new software that simulates Range and Doppler signals directly from the space-time metric. This flexible approach allows one to perform simulations in General Relativity and in alternative metric theories of gravity. In a second step, a least-squares fit of the different initial conditions involved in the situation is performed in order to compare anomalous signals produced by a given alternative theory with the ones obtained in General Relativity. This software provides orders of magnitude and signatures stemming from hypothetical alternative theories of gravity on radioscience signals. As an application, we present some simulations done for the Cassini mission in Post-Einsteinian Gravity and in the context of MOND External Field Effect. We deduce constraints on the Post-Einsteinian parameters but find that the considered arc of the Cassini mission is not useful to constrain the MOND External Field Effect.

#### Jan 25, 2012

1201.5041 (/preprints)
2012-01-25, 10:33 

## [1201.4656] Coherent follow-up of Continuous Gravitational Wave candidates: minimal required observation time

Authors: Miroslav Shaltev

Date: 23 Jan 2012

Abstract: We derive two different methods to compute the minimal required integration time of a fully coherent follow-up of candidates produced in wide parameter space semi-coherent searches, such as global correlation StackSlide searches using Einstein@Home. We numerically compare these methods in terms of integration duration and computing cost. In a Monte Carlo study we confirm that we can achieve the required detection probability.

#### Jan 24, 2012

1201.4656 (/preprints)
2012-01-24, 17:13 

## [1201.4413] Implications For The Origin Of GRB 051103 From LIGO Observations

Date: 21 Jan 2012

Abstract: We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.

#### Jan 24, 2012

1201.4413 (/preprints)
2012-01-24, 17:00 

## [1201.4389] Tidal Disruptions of White Dwarfs from Ultra-Close Encounters with Intermediate Mass Spinning Black Holes

Authors: Roland Haas, Roman V. Shcherbakov, Tanja Bode, Pablo Laguna

Date: 20 Jan 2012

Abstract: We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate mass black hole. These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole spin. However, the late-time accretion onto the black hole follows the same decay, $\dot{M}$ ~ tˆ{-5/3}, estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yrs after the disruption. For arbitrary black hole spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of ~3.2 Hz and strain amplitudes of ~10ˆ{-18} for galactic intermediate mass black holes. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in ROSAT all-sky survey. The future missions like Wide-Field X-ray Telescope (WFXT) could observe dozens of events.

#### Jan 24, 2012

1201.4389 (/preprints)
2012-01-24, 16:59 

## [1201.4321] Search for Continuous Gravitational Waves: Optimal StackSlide method at fixed computing cost

Authors: Reinhard Prix, Miroslav Shaltev

Date: 20 Jan 2012

Abstract: Coherent wide parameter-space searches for continuous gravitational waves are typically limited in sensitivity by their prohibitive computing cost. Therefore semi-coherent methods (such as StackSlide) can often achieve a better sensitivity. We develop an analytical method for finding optimal StackSlide parameters at fixed computing cost under ideal conditions of gapless data with Gaussian stationary noise. This solution separates two regimes: an unbounded regime, where it is always optimal to use all the data, and a bounded regime with a finite optimal observation time. Our analysis of the sensitivity scaling reveals that both the fine- and coarse-grid mismatches contribute equally to the average StackSlide mismatch, an effect that had been overlooked in previous studies. We discuss various practical examples for the application of this optimization framework, illustrating the potential gains in sensitivity compared to previous searches.

#### Jan 22, 2012

1201.4321 (/preprints)
2012-01-22, 22:47 

## [1201.3573] Extending burst searches with pulsar timing arrays

Authors: Matthew Pitkin

Date: 17 Jan 2012

Abstract: Pulsar timing arrays (PTAs) are being used to search for very low frequency gravitational waves. Gravitational waves imprint their signal in the observed pulse time of arrivals from when they passed the pulsar and as they pass the Earth. In searches for gravitational wave bursts with PTAs (e.g. Finn & Lommen, 2010) the pulsar term is generally ignored as only the Earth term will be coherent between all pulsars in the array, whereas signals in the pulsar terms may be separated by delays on the order of the pulsar distance. However, we show that for a set of pulsars (made up from those in the International Pulsar Timing Array) there are areas of the sky where the alignment between pairs, or more, of pulsars and a source are serendipitously placed to give pulsar terms that are separated by feasible (10-20 year) observing times. The data from these pulsars can therefore be coherently combined, with the appropriate sky position delay, to search for gravitational wave bursts. This increases the time-span over which bursts could be observed to be many times that covered by the PTA observation span. Assuming perfectly known pulsar distances we show that sources over approximately 70 per cent of the sky produce pulsar term signals separated by less than 10 years within at least one pair of pulsars. We study the effect of pulsar distance uncertainties on the sky coverage. We also assess a simplified method for detecting burst sources from these sky positions with a toy two-pulsar array.

#### Jan 19, 2012

1201.3573 (/preprints)
2012-01-19, 13:10 

## [1201.3563] A Mock Data Challenge for the Einstein Gravitational-Wave Telescope

Authors: Tania Regimbau, Thomas Dent, Walter Del Pozzo, Stefanos Giampanis, Tjonnie G. F. Li, Craig Robinson, Chris Van Den Broeck, Duncan Meacher, Carl Rodriguez, Bangalore S. Sathyaprakash, Katarzyna W&#xf3;jcik

Date: 17 Jan 2012

Abstract: Einstein Telescope (ET) is conceived to be a third generation gravitational-wave observatory. Its amplitude sensitivity would be a factor ten better than advanced LIGO and Virgo and it could also extend the low-frequency sensitivity down to 1--3\,Hz, compared to the 10--20\,Hz of advanced detectors. Such an observatory will have the potential to observe a variety of different GW sources, including compact binary systems at cosmological distances. ET's expected reach for binary neutron star (BNS) coalescences is out to redshift $z\simeq 2$ and the rate of detectable BNS coalescences could be as high as one every few tens or hundreds of seconds, each lasting up to several days. %in the sensitive frequency band of ET. With such a signal-rich environment, a key question in data analysis is whether overlapping signals can be discriminated. In this paper we simulate the GW signals from a cosmological population of BNS and ask the following questions: Does this population create a confusion background that limits ET's ability to detect foreground sources? How efficient are current algorithms in discriminating overlapping BNS signals? Is it possible to discern the presence of a population of signals in the data by cross-correlating data from different detectors in the ET observatory? We find that algorithms currently used to analyze LIGO and Virgo data are already powerful enough to detect the sources expected in ET, but new algorithms are required to fully exploit ET data.

#### Jan 19, 2012

1201.3563 (/preprints)
2012-01-19, 13:10 

## [1201.3407] Interaction of Recoiling Supermassive Black Holes with Stars in Galactic Nuclei

Authors: Shuo Li, F. K. Liu, Peter Berczik, Xian Chen, Rainer Spurzem

Date: 17 Jan 2012

Abstract: Supermassive black hole binaries (SMBHBs) are the products of frequent galaxy mergers. The coalescence of the SMBHBs is a distinct source of gravitational wave (GW) radiation. The detections of the strong GW radiation and their possible electromagnetic counterparts are essential. Numerical relativity suggests that the post-merger supermassive black hole (SMBH) gets a kick velocity up to 4000 km/s due to the anisotropic GW radiations. Here we investigate the dynamical co-evolution and interaction of the recoiling SMBHs and their galactic stellar environments with one million direct N-body simulations including the stellar tidal disruption by the recoiling SMBHs. Our results show that the accretion of disrupted stars does not significantly affect the SMBH dynamical evolution. We investigate the stellar tidal disruption rates as a function of the dynamical evolution of oscillating SMBHs in the galactic nuclei. Our simulations show that most of stellar tidal disruptions are contributed by the unbound stars and occur when the oscillating SMBHs pass through the galactic center. The averaged disruption rate is ~10ˆ{-6} M_\odot yrˆ{-1}, which is about an order of magnitude lower than that by a stationary SMBH at similar galactic nuclei. Our results also show that a bound star cluster is around the oscillating SMBH of about ~ 0.7% the black hole mass. In addition, we discover a massive cloud of unbound stars following the oscillating SMBH. We also investigate the dependence of the results on the SMBH masses and density slopes of the galactic nuclei.

#### Jan 19, 2012

1201.3407 (/preprints)
2012-01-19, 13:07 

## [1201.3621] eLISA: Astrophysics and cosmology in the millihertz regime

Authors: Pau Amaro-Seoane, Sofiane Aoudia, Stanislav Babak, Pierre Bin&#xe9;truy, Emanuele Berti, Alejandro Boh&#xe9;, Chiara Caprini, Monica Colpi, Neil J. Cornish, Karsten Danzmann, Jean-Fran&#xe7;ois Dufaux, Jonathan Gair, Oliver Jennrich, Philippe Jetzer, Antoine Klein, Ryan N. Lang, Alberto Lobo, Tyson Littenberg, Sean T. McWilliams, Gijs Nelemans, Antoine Petiteau, Edward K. Porter, Bernard F. Schutz, Alberto Sesana, Robin Stebbins, Tim Sumner, Michele Vallisneri, Stefano Vitale, Marta Volonteri, Henry Ward

Date: 17 Jan 2012

Abstract: This document introduces the exciting and fundamentally new science and astronomy that the European New Gravitational Wave Observatory (NGO) mission (derived from the previous LISA proposal) will deliver. The mission (which we will refer to by its informal name "eLISA") will survey for the first time the low-frequency gravitational wave band (about 0.1 mHz to 1 Hz), with sufficient sensitivity to detect interesting individual astrophysical sources out to z = 15. The eLISA mission will discover and study a variety of cosmic events and systems with high sensitivity: coalescences of massive black holes binaries, brought together by galaxy mergers; mergers of earlier, less-massive black holes during the epoch of hierarchical galaxy and black-hole growth; stellar-mass black holes and compact stars in orbits just skimming the horizons of massive black holes in galactic nuclei of the present era; extremely compact white dwarf binaries in our Galaxy, a rich source of information about binary evolution and about future Type Ia supernovae; and possibly most interesting of all, the uncertain and unpredicted sources, for example relics of inflation and of the symmetry-breaking epoch directly after the Big Bang. eLISA's measurements will allow detailed studies of these signals with high signal-to-noise ratio, addressing most of the key scientific questions raised by ESA's Cosmic Vision programme in the areas of astrophysics and cosmology. They will also provide stringent tests of general relativity in the strong-field dynamical regime, which cannot be probed in any other way. This document not only describes the science but also gives an overview on the mission design and orbits.

#### Jan 19, 2012

1201.3621 (/preprints)
2012-01-19, 13:04 

## [1201.1446] Hypervelocity Planets and Transits Around Hypervelocity Stars

Authors: Idan Ginsburg, Abraham Loeb, Gary A. Wegner

Date: 6 Jan 2012

Abstract: The disruption of a binary star system by the massive black hole at the Galactic Centre, SgrA*, can lead to the capture of one star around SgrA* and the ejection of its companion as a hypervelocity star (HVS). We consider the possibility that these stars may have planets and study the dynamics of these planets. Using a direct $N$-body integration code, we simulated a large number of different binary orbits around SgrA*. For some orbital parameters, a planet is ejected at a high speed. In other instances, a HVS is ejected with one or more planets orbiting around it. In these cases, it may be possible to observe the planet as it transits the face of the star. A planet may also collide with its host star. In such cases the atmosphere of the star will be enriched with metals. In other cases, a planet is tidally disrupted by SgrA*, leading to a bright flare.

#### Jan 17, 2012

1201.1446 (/preprints)
2012-01-17, 14:55 

## [1201.1414] Physics of the Galactic Center Cloud G2, on its Way towards the Super-Massive Black Hole

Authors: Andreas Burkert, Mark Schartmann, Christian Alig, Stefan Gillessen, Reinhard Genzel, Tobias Fritz, Frank Eisenhauer

Date: 6 Jan 2012

Abstract: The origin, structure and evolution of the small gas cloud, G2, is investigated, that is on an orbit almost straight into the Galactic central supermassive black hole (SMBH). G2 is a sensitive probe of the hot accretion zone of Sgr A*, requiring gas temperatures and densities that agree well with models of captured shock-heated stellar winds. Its mass is equal to the critical mass below which cold clumps would be destroyed quickly by evaporation. Its mass is also constrained by the fact that at apocenter its sound crossing timescale was equal to its orbital timescale. Our numerical simulations show that the observed structure and evolution of G2 can be well reproduced if it formed in pressure equilibrium with the surrounding in 1995 at a distance from the SMBH of 7.6e16 cm. If the cloud would have formed at apocenter in the 'clockwise' stellar disk as expected from its orbit, it would be torn into a very elongated spaghetti-like filament by 2011 which is not observed. This problem can be solved if G2 is the head of a larger, shell-like structure that formed at apocenter. Our numerical simulations show that this scenario explains not only G2's observed kinematical and geometrical properties but also the Br_gamma observations of a low surface brightness gas tail that trails the cloud. In 2013, while passing the SMBH G2 will break up into a string of droplets that within the next 30 years mix with the surrounding hot gas and trigger cycles of AGN activity.

#### Jan 17, 2012

1201.1414 (/preprints)
2012-01-17, 14:54 

## [gr-qc/0508052] In an expanding universe, what doesn't expand?

Authors: Richard H. Price, Joseph D. Romano

Date: 12 Aug 2005

Abstract: The expansion of the universe is often viewed as a uniform stretching of space that would affect compact objects, atoms and stars, as well as the separation of galaxies. One usually hears that bound systems do not take part in the general expansion, but a much more subtle question is whether bound systems expand partially. In this paper, a very definitive answer is given for a very simple system: a classical "atom" bound by electrical attraction. With a mathemical description appropriate for undergraduate physics majors, we show that this bound system either completely follows the cosmological expansion, or -- after initial transients -- completely ignores it. This "all or nothing" behavior can be understood with techniques of junior-level mechanics. Lastly, the simple description is shown to be a justifiable approximation of the relativistically correct formulation of the problem.

#### Jan 17, 2012

0508052 (/preprints/gr-qc)
2012-01-17, 14:53 

## [1201.3238] Science performance of Gaia, ESA's space-astrometry mission

Authors: J. H. J. de Bruijne

Date: 16 Jan 2012

Abstract: Gaia is the next astrometry mission of the European Space Agency (ESA), following up on the success of the Hipparcos mission. With a focal plane containing 106 CCD detectors, Gaia will survey the entire sky and repeatedly observe the brightest 1,000 million objects, down to 20th magnitude, during its 5-year lifetime. Gaia's science data comprises absolute astrometry, broad-band photometry, and low-resolution spectro-photometry. Spectroscopic data with a resolving power of 11,500 will be obtained for the brightest 150 million sources, down to 17th magnitude. The thermo-mechanical stability of the spacecraft, combined with the selection of the L2 Lissajous point of the Sun-Earth/Moon system for operations, allows stellar parallaxes to be measured with standard errors less than 10 micro-arcsecond (muas) for stars brighter than 12th magnitude, 25 muas for stars at 15th magnitude, and 300 muas at magnitude 20. Photometric standard errors are in the milli-magnitude regime. The spectroscopic data allows the measurement of radial velocities with errors of 15 km/s at magnitude 17. Gaia's primary science goal is to unravel the kinematical, dynamical, and chemical structure and evolution of the Milky Way. In addition, Gaia's data will touch many other areas of science, e.g., stellar physics, solar-system bodies, fundamental physics, and exo-planets. The Gaia spacecraft is currently in the qualification and production phase. With a launch in 2013, the final catalogue is expected in 2021. The science community in Europe, organised in the Data Processing and Analysis Consortium (DPAC), is responsible for the processing of the data.

#### Jan 17, 2012

1201.3238 (/preprints)
2012-01-17, 14:49 

## [1201.3176] Searches for continuous gravitational wave signals and stochastic backgrounds in LIGO and Virgo data

Authors: C. Palomba, for the LIGO Scientific Collaboration, for the Virgo Collaboration

Date: 16 Jan 2012

Abstract: We present results from searches of recent LIGO and Virgo data for continuous gravitational wave signals (CW) from spinning neutron stars and for a stochastic gravitational wave background (SGWB). The first part of the talk is devoted to CW analysis with a focus on two types of searches. In the targeted search of known neutron stars a precise knowledge of the star parameters is used to apply optimal filtering methods. In the absence of a signal detection, in a few cases, an upper limit on strain amplitude can be set that beats the spindown limit derived from attributing spin-down energy loss to the emission of gravitational waves. In contrast, blind all-sky searches are not directed at specific sources, but rather explore as large a portion of the parameter space as possible. Fully coherent methods cannot be used for these kind of searches which pose a non trivial computational challenge. The second part of the talk is focused on SGWB searches. A stochastic background of gravitational waves is expected to be produced by the superposition of many incoherent sources of cosmological or astrophysical origin. Given the random nature of this kind of signal, it is not possible to distinguish it from noise using a single detector. A typical data analysis strategy relies on cross-correlating the data from a pair or several pairs of detectors, which allows discriminating the searched signal from instrumental noise. Expected sensitivities and prospects for detection from the next generation of interferometers are also discussed for both kind of sources.

#### Jan 17, 2012

1201.3176 (/preprints)
2012-01-17, 14:49 

## [1201.2959] Likelihood-ratio ranking of gravitational-wave candidates in a non-Gaussian background

Authors: Rahul Biswas, Patrick R. Brady, Jordi Burguet-Castell, Kipp Cannon, Jessica Clayton, Alexander Dietz, Nickolas Fotopoulos, Lisa M. Goggin, Drew Keppel, Chris Pankow, Larry R. Price, Ruslan Vaulin

Date: 13 Jan 2012

Abstract: There is a broad class of astrophysical sources that produce detectable, transient, gravitational waves. Some searches for transient gravitational waves are tailored to known features of these sources. Other searches make few assumptions about the sources. Typically events are observable with multiple search techniques. This work describes how to combine the results of searches that are not independent, treating each search as a classifier for a given event. This will be shown to improve the overall sensitivity to gravitational-wave events while directly addressing the problem of consistent interpretation of multiple trials.

#### Jan 17, 2012

1201.2959 (/preprints)
2012-01-17, 14:49 

## [1201.2079] The information paradox: conflicts and resolutions

Authors: Samir D. Mathur

Date: 10 Jan 2012

Abstract: Many relativists have been long convinced that black hole evaporation leads to information loss or remnants. String theorists have however not been too worried about the issue, largely due to a belief that the Hawking argument for information loss is flawed in its details. A recently derived inequality shows that the Hawking argument for black holes with horizon can in fact be made rigorous. What happens instead is that in string theory black hole microstates have no horizons. Thus the evolution of radiation quanta with E ~ kT is modified by order unity at the horizon, and we resolve the information paradox. We discuss how it is still possible for E >> kT objects to see an approximate black hole like geometry. We also note some possible implications of this physics for the early Universe.

#### Jan 17, 2012

1201.2079 (/preprints)
2012-01-17, 14:49 

## [1201.2858] Gravitational wave diagnosis of a circumbinary disk

Authors: Kimitake Hayasaki, Kent Yagi, Takahiro Tanaka, Shin Mineshige

Date: 13 Jan 2012

Abstract: When binary black holes are embedded in a gaseous environment, a rotating disk surrounding them, the so-called circumbinary disk, will be formed. The binary exerts a gravitational torque on the circumbinary disk and thereby the orbital angular momentum is transferred to it, while the angular momentum of the circumbinary disk is transferred to the binary through the mass accretion. The binary undergoes an orbital decay due to both the gravitational wave emission and the binary-disk interaction. This causes the phase evolution of the gravitational wave signal. The precise measurement of the gravitational wave phase thus may provide information regarding the circumbinary disk. In this paper, we assess the detectability of the signature of the binary-disk interaction using the future space-borne gravitational wave detectors such as DECIGO and BBO by the standard matched filtering analysis. We find that the effect of the circumbinary disk around binary black holes in the mass range $6M_sun\le{M}\lesssim3\times10ˆ3M_sun$ is detectable at a statistically significant level in five year observation, provided that gas accretes onto the binary at a rate greater than $\dot{M}\sim1.4\times10ˆ{17} [gsˆ{-1}] jˆ{-1}(M/10M_sun)ˆ{33/23}$ with 10% mass-to-energy conversion efficiency, where j represents the efficiency of the angular momentum transfer from the binary to the circumbinary disk. We show that $O(0.1)$ coalescence events are expected to occur in sufficiently dense molecular clouds in five year observation. We also point out that the circumbinary disk is detectable, even if its mass at around the inner edge is by over 10 orders of magnitude less than the binary mass.

#### Jan 17, 2012

1201.2858 (/preprints)
2012-01-17, 14:49 

## [1201.2759] Tensor-vector-scalar-modified gravity: from small scale to cosmology

Authors: Jacob D. Bekenstein

Date: 13 Jan 2012

Abstract: The impressive success of the standard cosmological model has suggested to many that its ingredients are all one needs to explain galaxies and their systems. I summarize a number of known problems with this program. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the MOND paradigm which has proved an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the nonrelativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first sidestepped with the formulation of TeVeS, a covariant modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in face of galaxy phenomenology. I also summarize features of TeVeS cosmology and describe the confrontation with data from strong and weak gravitational lensing

#### Jan 17, 2012

1201.2759 (/preprints)
2012-01-17, 14:49 

## [1201.2964] Detecting transient gravitational waves in non-Gaussian noise with partially redundant analysis methods

Authors: Rahul Biswas, Patrick R. Brady, Jordi Burguet-Castell, Kipp Cannon, Jessica Clayton, Alexander Dietz, Nickolas Fotopoulos, Lisa M. Goggin, Drew Keppel, Chris Pankow, Larry R. Price, Ruslan Vaulin

Date: 13 Jan 2012

Abstract: There is a broad class of astrophysical sources that produce detectable, transient, gravitational waves. Some searches for transient gravitational waves are tailored to known features of these sources. Other searches make few assumptions about the sources. Typically events are observable with multiple search techniques. This work describes how to combine the results of searches that are not independent, treating each search as a classifier for a given event. This will be shown to improve the overall sensitivity to gravitational-wave events while directly addressing the problem of consistent interpretation of multiple trials.

#### Jan 17, 2012

1201.2964 (/preprints)
2012-01-17, 14:49 

## [1201.1923] Gravitational Recoil From Accretion-Aligned Black-Hole Binaries

Authors: Carlos O. Lousto, Yosef Zlochower, Massimo Dotti, Marta Volonteri

Date: 9 Jan 2012

Abstract: We explore the newly discovered "hangup-kick" effect, which greatly amplifies the recoil for configuration with partial spin- orbital-angular momentum alignment, by studying a set of 48 new simulations of equal-mass, spinning black-hole binaries. We propose a phenomenological model for the recoil that takes this new effect into account and then use this model, in conjunction with statistical distributions for the spin magnitude and orientations, based on accretion simulations, to find the probabilities for observing recoils of several thousand km/s. In addition, we provide initial parameters, eccentricities, radiated linear and angular momentum, precession rates and remnant mass, spin, and recoils for all 48 configurations. Our results indicate that surveys exploring peculiar (redshifted or blueshifted) differential line-of-sight velocities should observe at least one case above 2000 km/s out of four thousand merged galaxies. The probability that a remnant BH receives a total recoil exceeding the ~2000 km/s escape velocity of large elliptical galaxies is ten times larger. Probabilities of recoils exceeding the escape velocity quickly rise to 5% for galaxies with escape velocities of 1000 km/s and nearly 20% for galaxies with escape velocities of 500 km/s. In addition the direction of these large recoils is strongly peaked toward the angular momentum axis, with very low probabilities of recoils exceeding 350 km/s for angles larger than 45 deg. with respect to the orbital angular momentum axis.

#### Jan 17, 2012

1201.1923 (/preprints)
2012-01-17, 14:49 

## [1201.2101] Constraining the physics of the r-mode instability in neutron stars with X-ray and UV observations

Authors: Brynmor Haskell, Nathalie Degenaar, Wynn C.G. Ho

Date: 10 Jan 2012

Abstract: Rapidly rotating Neutron Stars in Low Mass X-ray Binaries (LMXBs) may be an interesting source of Gravitational Waves (GWs). In particular, several modes of stellar oscillation may be driven unstable by GW emission, and this can lead to a detectable signal. Here we illustrate how current X-ray and ultra-violet (UV) observations can constrain the physics of the r-mode instability. We show that the core temperatures inferred from the data would place many systems well inside the unstable region predicted by standard physical models. However, this is at odds with theoretical expectations. We discuss different mechanisms that could be at work in the stellar interior, and we show how they can modify the instability window and make it consistent with the inferred temperatures.

#### Jan 17, 2012

1201.2101 (/preprints)
2012-01-17, 14:49 

## [1201.2113] Is J enough? Comparison of gravitational waves emitted along the total angular momentum direction with other preferred orientations

Authors: R. O&#x27;Shaughnessy (1), J. Healy (2), L. London (2), Z. Meeks (2), D. Shoemaker (2) ((1) Center for Gravitation and Cosmology, University of Wisconsin-Milwaukee, (2) Center for Relativistic Astrophysics, Georgia Tech)

Date: 10 Jan 2012

Abstract: The gravitational wave signature emitted from a merging binary depends on the orientation of an observer relative to the binary. Previous studies suggest that emission along the total initial or total final angular momenta leads to both the strongest and simplest signal from a precessing compact binary. In this paper we describe a concrete counterexample: a binary with $m_1/m_2=4$, $a_1=0.6 \hat{x} = -a_2$, placed in orbit in the x,y plane. We extract the gravitational wave emission along several proposed emission directions, including the initial (Newtonian) orbital angular momentum; the final (~ initial) total angular momentum; and the dominant principal axis of $<L_a L_b>_M$. Using several diagnostics, we show that the suggested preferred directions are not representative. For example, only for a handful of other directions (< 15%) will the gravitational wave signal have comparable shape to the one extracted along each of these fiducial directions, as measured by a generalized overlap (>0.95). We conclude that the information available in just one direction (or mode) does not adequately encode the complexity of orientation-dependent emission for even short signals from merging black hole binaries. Future investigations of precessing, unequal-mass binaries should carefully explore and model their orientation-dependent emission.

#### Jan 17, 2012

1201.2113 (/preprints)
2012-01-17, 14:48 

## [1201.1739] Use of Singular-Value Decomposition in Gravitational-Wave Data Analysis

Authors: Drew Keppel

Date: 9 Jan 2012

Abstract: Singular-value decomposition is a powerful technique that has been used in the analysis of matrices in many fields. In this paper, we summarize how it has been applied to the analysis of gravitational-wave data. These include producing basis waveforms for matched filtering, decreasing the computational cost of searching for many waveforms, improving parameter estimation, and providing a method of waveform interpolation.

#### Jan 17, 2012

1201.1739 (/preprints)
2012-01-17, 14:48 

## [1201.1697] Modifying Gravity: You Can't Always Get What You Want

Authors: Glenn D. Starkman

Date: 9 Jan 2012

Abstract: The combination of GR and the Standard Model disagrees with numerous observations on scales from our Solar System up. In the concordance model of cosmology, these contradictions are removed or alleviated by the introduction of three completely independent new components of stress-energy -- the inflaton, dark matter, and dark energy. Each of these in its turn is meant to have (or to currently) dominate the dynamics of the universe. There is still no non-gravitational evidence for any of these dark sectors; nor for the required extensions of the standard model. An alternative is to imagine that GR itself must be modified. Certain coincidences of scale even suggest that one might expect not to have to make three independent. Because they must address the most different types of data, attempts to replace dark matter with modified gravity are the most controversial. A phenomenological model (or family of models), Modified Newtonian Dynamics, has, over the last few years seen several covariant realizations. We discuss a number of challenges that any model that seeks to replace dark matter with modified gravity must face: the loss of Birkhoff's Theorem, and the calculational simplifications it implies; the failure to explain clusters, whether static or interacting, and the consequent need to introduce dark matter of some form, whether hot dark matter neutrinos, or dark fields that arise in new sectors of the modified gravity theory; the intrusion of cosmological expansion into the modified force law, that arises precisely because of the coincidence in scale between the centripetal acceleration at which Newtonian gravity fails in galaxies, and the cosmic acceleration. We conclude with the observation that, although modified gravity may indeed manage to replace dark matter, it is likely to do so by becoming or incorporating, a dark matter theory itself.

#### Jan 17, 2012

1201.1697 (/preprints)
2012-01-17, 14:48 

## [1201.1006] On the Mass Distribution and Birth Masses of Neutron Stars

Authors: Feryal Ozel (Arizona), Dimitrios Psaltis (Arizona), Ramesh Narayan (Harvard), Antonio Santos Villarreal (Arizona)

Date: 4 Jan 2012

Abstract: We investigate the distribution of neutron star masses in different populations of binaries, employing Bayesian statistical techniques. In particular, we explore the differences in neutron star masses between sources that have experienced distinct evolutionary paths and accretion episodes. We find that the distribution of neutron star masses in non-recycled eclipsing high-mass binaries as well as of slow pulsars, which are all believed to be near their birth masses, has a mean of 1.28 M_solar and a dispersion of 0.24 M_solar. These values are consistent with expectations for neutron star formation in core-collapse supernovae. On the other hand, double neutron stars, which are also believed to be near their birth masses, have a much narrower mass distribution, peaking at 1.33 M_solar but with a dispersion of only 0.06 M_solar. Such a small dispersion cannot easily be understood and perhaps points to a particular and rare formation channel. The mass distribution of neutron stars that have been recycled has a mean of 1.48 M_solar and a dispersion of 0.2 M_solar, consistent with the expectation that they have experienced extended mass accretion episodes. The fact that only a very small fraction of recycled neutron stars in the inferred distribution have masses that exceed ~2 M_solar suggest that only a few of these neutron stars cross the mass threshold to form low mass black holes.

#### Jan 06, 2012

1201.1006 (/preprints)
2012-01-06, 10:27 

## [1201.1195] Estimating parameters of coalescing compact binaries with proposed advanced detector networks

Authors: J. Veitch, I. Mandel, B. Aylott, B. Farr, V. Raymond, C. Rodriguez, M. van der Sluys, V. Kalogera, A. Vecchio

Date: 5 Jan 2012

Abstract: The advanced versions of the LIGO and Virgo ground-based gravitational-wave detectors are expected to operate from three sites: Hanford, Livingston, and Cascina. Recent proposals have been made to place a fourth site in Australia or India; and there is the possibility of using the Large Cryogenic Gravitational Wave Telescope in Japan to further extend the network. Using Bayesian parameter-estimation analyses of simulated gravitational-wave signals from a range of coalescing-binary locations and orientations at fixed distance or signal-to-noise ratio, we study the improvement in parameter estimation for the proposed networks. We find that a fourth detector site can break degeneracies in several parameters; in particular, the localization of the source on the sky is improved by a factor of ~ 3--4 for an Australian site, or ~ 2.5--3.5 for an Indian site, with more modest improvements in distance and binary inclination estimates. This enhanced ability to localize sources on the sky will be crucial in any search for electromagnetic counterparts to detected gravitational-wave signals.

#### Jan 06, 2012

1201.1195 (/preprints)
2012-01-06, 10:27 

## [1201.0983] Cosmological Backgrounds of Gravitational Waves and eLISA/NGO: Phase Transitions, Cosmic Strings and Other Sources

Authors: Pierre Bin&#xe9;truy, Alejandro Boh&#xe9;, Chiara Caprini, Jean-Fran&#xe7;ois Dufaux

Date: 4 Jan 2012

Abstract: We review the main cosmological backgrounds of gravitational waves accessible to detectors in space sensitive to the range $10ˆ{-4}$ to $10ˆ{-1}$ Hz, with a special emphasis on those backgrounds due to phase transitions or networks of cosmic strings. We apply this to identify the scientific potential of the NGO/eLISA mission of ESA, regarding the detectability of such cosmological backgrounds.

#### Jan 05, 2012

1201.0983 (/preprints)
2012-01-05, 09:41 

## [1112.4903] Gravitational radiation from compact binary systems in the massive Brans-Dicke theory of gravity

Authors: Justin Alsing, Emanuele Berti, Clifford Will, Helmut Zaglauer

Date: 21 Dec 2011

Abstract: We derive the equations of motion, the periastron shift, and the gravitational radiation damping for quasicircular compact binaries in a massive variant of the Brans-Dicke theory of gravity. We also study the Shapiro time delay and the Nordtvedt effect in this theory. By comparing with recent observational data, we put bounds on the two parameters of the theory: the Brans-Dicke coupling parameter \omega_{BD} and the scalar mass m_s. We find that the most stringent bounds come from Cassini measurements of the Shapiro time delay in the Solar System, that yield a lower bound \omega_{BD}>40000 for scalar masses m_s<2.5x10ˆ{-20} eV, to 95% confidence. In comparison, observations of the Nordtvedt effect using Lunar Laser Ranging (LLR) experiments yield \omega_{BD}>1000 for m_s<2.5x10ˆ{-20} eV. Observations of the orbital period derivative of the quasicircular white dwarf-neutron star binary PSR J1012+5307 yield \omega_{BD}>1250 for m_s<10ˆ{-20} eV. A first estimate suggests that bounds comparable to the Shapiro time delay may come from observations of radiation damping in the eccentric white dwarf-neutron star binary PSR J1141-6545, but a quantitative prediction requires the extension of our work to eccentric orbits.

#### Jan 03, 2012

1112.4903 (/preprints)
2012-01-03, 08:44 

## [1112.6355] Generic effective source for scalar self-force calculations

Authors: Barry Wardell, Ian Vega, Jonathan Thornburg, Peter Diener

Date: 29 Dec 2011

Abstract: A leading approach to the modelling of extreme mass ratio inspirals involves the treatment of the smaller mass as a point particle and the computation of a regularized self-force acting on that particle. In turn, this computation requires knowledge of the regularized retarded field generated by the particle. A direct calculation of this regularized field may be achieved by replacing the point particle with an effective source and solving directly a wave equation for the regularized field. This has the advantage that all quantities are finite and require no further regularization. In this work, we present a method for computing an effective source which is finite and continuous everywhere, and which is valid for a scalar point particle in arbitrary geodesic motion in an arbitrary background spacetime. We explain in detail various technical and practical considerations that underlie its use in several numerical self-force calculations. We consider as examples the cases of a particle in a circular orbit about Schwarzschild and Kerr black holes, and also the case of a particle following a generic time-like geodesic about a highly spinning Kerr black hole. We provide numerical C code for computing an effective source for various orbital configurations about Schwarzschild and Kerr black holes.

#### Jan 03, 2012

1112.6355 (/preprints)
2012-01-03, 08:42 

## [1112.6005] First Low-Latency LIGO Virgo Search for Binary Inspirals and their Electromagnetic Counterparts

Authors: The LIGO Scientific Collaboration, The Virgo Collaboration

Date: 27 Dec 2011

Abstract: Aims. The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy.
Methods. During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere.
Results. Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data.

#### Jan 03, 2012

1112.6005 (/preprints)
2012-01-03, 08:42