**Authors**: Adam Pound

**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.

1206.6538
(/preprints)

2012-06-28, 22:29
**[edit]**

**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.

1206.6163
(/preprints)

2012-06-28, 10:16
**[edit]**

**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.

1206.6167
(/preprints)

2012-06-28, 10:16
**[edit]**

**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.

1206.5331
(/preprints)

2012-06-27, 10:54
**[edit]**

**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.

1206.4722
(/preprints)

2012-06-26, 11:10
**[edit]**

**Authors**: R. Szcz\keśniak, 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 $R_{1}(p)$.

1206.5531
(/preprints)

2012-06-26, 07:52
**[edit]**

**Authors**: Balázs Mikóczi, Bence Kocsis, Péter Forgács, Mátyás Vasúth

**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 $e_0 \sim 0.3$.

1206.5786
(/preprints)

2012-06-25, 22:38
**[edit]**

**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.

1206.4949
(/preprints)

2012-06-24, 22:55
**[edit]**

**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.

1206.5058
(/preprints)

2012-06-24, 22:54
**[edit]**

**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.

1206.5229
(/preprints)

2012-06-24, 22:54
**[edit]**

**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.

1206.4316
(/preprints)

2012-06-21, 09:42
**[edit]**

**Authors**: Pablo A. Rosado

**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.

1206.1330
(/preprints)

2012-06-20, 12:20
**[edit]**

**Authors**: Jérôme Carré, 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".

1206.2509
(/preprints)

2012-06-20, 12:19
**[edit]**

**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.

1206.2397
(/preprints)

2012-06-20, 12:18
**[edit]**

**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.

1206.3461
(/preprints)

2012-06-20, 12:18
**[edit]**

**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 $10ˆ{-5}$.

1206.2943
(/preprints)

2012-06-20, 12:18
**[edit]**

**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.

1206.3015
(/preprints)

2012-06-20, 12:17
**[edit]**

**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.

1206.3077
(/preprints)

2012-06-20, 12:17
**[edit]**

**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.

1206.3803
(/preprints)

2012-06-20, 12:16
**[edit]**

**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.

1206.0703
(/preprints)

2012-06-07, 01:18
**[edit]**

**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.

1206.0660
(/preprints)

2012-06-07, 01:17
**[edit]**

**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.

1206.0322
(/preprints)

2012-06-07, 01:16
**[edit]**

**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. Lück, 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. Müller-Ebhardt, P. Murray, L. Naticchioni, R. Nawrodt, J. Nelson, R. O'. 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. Rüdiger, A. Samblowski, L. Santamaría, 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. Thürin, 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. Weßels, 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.

1206.0331
(/preprints)

2012-06-07, 01:16
**[edit]**

**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.

1206.0915
(/preprints)

2012-06-07, 01:14
**[edit]**

**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.

1206.0744
(/preprints)

2012-06-07, 01:12
**[edit]**

**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.

1206.0818
(/preprints)

2012-06-07, 01:12
**[edit]**

**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.

1206.1225
(/preprints)

2012-06-07, 01:11
**[edit]**

**Authors**: An\il Zenginoğlu, 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.

1206.1109
(/preprints)

2012-06-07, 01:11
**[edit]**

**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.

1206.1056
(/preprints)

2012-06-07, 01:09
**[edit]**

**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.

1206.0028
(/preprints)

2012-06-04, 02:11
**[edit]**

**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).

1205.5268
(/preprints)

2012-06-01, 18:05
**[edit]**

**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.

1205.5562
(/preprints)

2012-06-01, 18:04
**[edit]**

**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 $\sim (m_1/m_2)ˆ{-5.25}$.

1205.6009
(/preprints)

2012-06-01, 18:03
**[edit]**

**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.

1205.6215
(/preprints)

2012-06-01, 18:03
**[edit]**

**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.

1205.7063
(/preprints)

2012-06-01, 18:02
**[edit]**

**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.

1205.6592
(/preprints)

2012-06-01, 18:02
**[edit]**

**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.

1205.6611
(/preprints)

2012-06-01, 18:02
**[edit]**

**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.

1205.7006
(/preprints)

2012-06-01, 18:01
**[edit]**

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

*Tantum in modicis, quantum in maximis*