**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.

1212.5996
(/preprints)

2012-12-26, 20:24
**[edit]**

**Authors**: Márton Tápai, Zoltán Keresztes, László Á. 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.

1212.4973
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.5202
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.4730
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.5053
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.4357
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.4810
(/preprints)

2012-12-21, 13:03
**[edit]**

**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.

1212.3342
(/preprints)

2012-12-17, 09:41
**[edit]**

**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.

1212.3169
(/preprints)

2012-12-13, 18:40
**[edit]**

**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.

1212.2289
(/preprints)

2012-12-13, 08:46
**[edit]**

**Authors**: Adam Helfer

**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.

1212.2926
(/preprints)

2012-12-13, 08:46
**[edit]**

**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.

1212.1235
(/preprints)

2012-12-13, 08:45
**[edit]**

**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.

1212.2623
(/preprints)

2012-12-13, 08:45
**[edit]**

**Authors**: Orfeu Bertolami, Jorge Páramos

**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.

1212.2177
(/preprints)

2012-12-13, 08:45
**[edit]**

**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.

1212.1191
(/preprints)

2012-12-13, 08:44
**[edit]**

**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.

1212.0837
(/preprints)

2012-12-13, 08:44
**[edit]**

**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.

1211.6427
(/preprints)

2012-12-04, 18:33
**[edit]**

**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.

1212.0232
(/preprints)

2012-12-04, 18:33
**[edit]**

**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.

1211.7099
(/preprints)

2012-12-03, 11:01
**[edit]**

**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.

1211.7090
(/preprints)

2012-12-03, 11:01
**[edit]**

**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.

1211.7183
(/preprints)

2012-12-03, 11:01
**[edit]**

**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.

1211.7095
(/preprints)

2012-12-03, 11:01
**[edit]**

© M. Vallisneri 2012 — last modified on 2010/01/29

*Tantum in modicis, quantum in maximis*