## [0801.4185] Polarization analysis of gravitational-wave backgrounds from the correlation signals of ground-based interferometers: measuring a circular-polarization mode

Authors: Naoki Seto, Atsushi Taruya

Date: 28 Jan 2008

Abstract: The Stokes V parameter characterizes asymmetry of amplitudes between right- and left-handed waves, and non-vanishing value of the V parameter yields a circularly polarized signal. Cosmologically, V parameter may be a direct probe for parity violation in the universe. In this paper, we theoretically investigate a measurement of this parameter, particularly focusing on the gravitational-wave backgrounds observed via ground-based interferometers. In contrast to the traditional analysis that only considers the total amplitude (or equivalently $\Omega_{GW}$), the signal analysis including a circular-polarized mode has a rich structure due to the multi-dimensionality of target parameters. We show that, by using the network of next-generation detectors, separation between polarized and unpolarized modes can be performed with small statistical loss induced by their correlation.

#### Jan 31, 2008

0801.4185 (/preprints)
2008-01-31, 10:11 

## [0712.2332] From Geometry to Numerics: interdisciplinary aspects in mathematical and numerical relativity

Authors: J.L. Jaramillo, J.A. Valiente Kroon, E. Gourgoulhon

Date: 14 Dec 2007

Abstract: This article reviews some aspects in the current relationship between mathematical and numerical General Relativity. Focus is placed on the description of isolated systems, with a particular emphasis on recent developments in the study of black holes. Ideas concerning asymptotic flatness, the initial value problem, the constraint equations, evolution formalisms, geometric inequalities and quasi-local black hole horizons are discussed on the light of the interaction between numerical and mathematical relativists.

#### Jan 31, 2008

0712.2332 (/preprints)
2008-01-31, 10:11 

## [0801.4313] A Bayesian approach to the follow-up of candidate gravitational wave signals

Authors: John Veitch, Alberto Vecchio

Date: 28 Jan 2008

Abstract: Ground-based gravitational wave laser interferometers (LIGO, GEO-600, Virgo and Tama-300) have now reached high sensitivity and duty cycle. We present a Bayesian evidence-based approach to the search for gravitational waves, in particular aimed at the followup of candidate events generated by the analysis pipeline. We introduce and demonstrate an efficient method to compute the evidence and odds ratio between different models, and illustrate this approach using the specific case of the gravitational wave signal generated during the inspiral phase of binary systems, modelled at the leading quadrupole Newtonian order, in synthetic noise. We show that the method is effective in detecting signals at the detection threshold and it is robust against (some types of) instrumental artefacts. The computational efficiency of this method makes it scalable to the analysis of all the triggers generated by the analysis pipelines to search for coalescing binaries in surveys with ground-based interferometers, and to a whole variety of signal waveforms, characterised by a larger number of parameters.

#### Jan 28, 2008

0801.4313 (/preprints)
2008-01-28, 21:32 

## [0801.4297] Method to estimate ISCO and ring-down frequencies in binary systems and consequences for gravitational wave data analysis

Authors: Chad Hanna, Miguel Megevand, Evan Ochsner, Carlos Palenzuela

Date: 28 Jan 2008

Abstract: Recent advances in the description of compact binary systems have produced gravitational waveforms that include inspiral, merger and ring-down phases. Comparing results from numerical simulations with those of post-Newtonian (PN), and related, expansions has provided motivation for employing PN waveforms in near merger epochs when searching for gravitational waves and has encouraged the development of analytic fits to full numerical waveforms. The models and simulations do not yet cover the full binary coalescence parameter space. For these yet un-simulated regions, data analysts can still conduct separate inspiral, merger and ring-down searches. Improved knowledge about the end of the inspiral phase, the beginning of the merger, and the ring-down frequencies could increase the efficiency of both coherent inspiral-merger-ring-down (IMR) searches and searches over each phase separately. Insight can be gained for all three cases through a recently presented theoretical calculation, which, corroborated by the numerical results, provides an implicit formula for the final spin of the merged black holes, accurate to within 10% over a large parameter space. Knowledge of the final spin allows one to predict the end of the inspiral phase and the quasinormal mode ring-down frequencies, and in turn provides information about the bandwidth and duration of the merger. In this work we will discuss a few of the implications of this calculation for data analysis.

#### Jan 28, 2008

0801.4297 (/preprints)
2008-01-28, 21:32 

## [0801.4149] Optimal Location of Two Laser-interferometric Detectors for Gravitational Wave Backgrounds at 100 MHz

Authors: Atsushi Nishizawa, Seiji Kawamura, Tomotada Akutsu, Koji Arai, Kazuhiro Yamamoto, Daisuke Tatsumi, Erina Nishida, Masa-aki Sakagami, Takeshi Chiba, Ryuichi Takahashi, Naoshi Sugiyama

Date: 27 Jan 2008

Abstract: Recently, observational searches for gravitational wave background (GWB) have been developed and given constraints on the energy density of GWB in a broad range of frequencies. These constraints have already resulted in the rejection of some theoretical models of relatively large GWB spectra. However, at 100 MHz, there is no strict upper limit from direct observation, though an indirect limit exists due to He4 abundance due to big-bang nucleosynthesis. In our previous paper, we investigated the detector designs that can effectively respond to GW at high frequencies, where the wavelength of GW is comparable to the size of a detector, and found that the configuration, a so-called synchronous-recycling interferometer is best at these sensitivity. In this paper, we investigated the optimal location of two synchronous-recycling interferometers and derived their cross-correlation sensitivity to GWB. We found that the sensitivity is nearly optimized and hardly changed if two coaligned detectors are located within a range 0.2 m, and that the sensitivity achievable in an experiment is far below compared with the constraint previously obtained in experiments.

#### Jan 28, 2008

0801.4149 (/preprints)
2008-01-28, 21:32 

## [0801.4070] Building a stochastic template bank for detecting massive black hole binaries

Authors: Stanislav Babak

Date: 26 Jan 2008

Abstract: Coalescence of two massive black holes is the strongest and most promising source for LISA. In fact, gravitational signal from the end of inspiral and merger will be detectable throughout the Universe. In this article we describe the first step in the two-step hierarchical search for gravitational wave signal from the inspiraling massive BH binaries. It is based on the routinely used in the ground base gravitational wave astronomy method of filtering the data through the bank of templates. However we use a novel Monte-Carlo based (stochastic) method to lay a grid in the parameter space, and we use the likelihood maximized analytically over some parameters, known as F-statistic, as a detection statistic. We build a coarse template bank to detect gravitational wave signals and to make preliminary parameter estimation. The best candidates will be followed up using Metropolis-Hasting stochastic search to refine the parameter estimation. We demonstrate the performance of the method by applying it to the Mock LISA data challenge 1B (training data set).

#### Jan 28, 2008

0801.4070 (/preprints)
2008-01-28, 21:31 

## [0801.3859] Determining the Dimensionality of Spacetime by Gravitational Lensing

Authors: Jop Briet, David Hobill

Date: 24 Jan 2008

Abstract: The physics associated with spherically symmetric charged black holes is analyzed from the point of view of using weak gravitational lensing as a means for determining the dimensionality of spacetime. In particular, for exact solutions of electro-vac black holes in four and five spacetime dimensions the motion of photons is studied using the equations for the null geodesics and deriving the weak limit bending angles and delays in photon arrival times.

#### Jan 28, 2008

0801.3859 (/preprints)
2008-01-28, 21:30 

## [0801.3478] Probing the Binary Black Hole Merger Regime with Scalar Perturbations

Authors: Eloisa Bentivegna, Deirdre M. Shoemaker, Ian Hinder, Frank Herrmann

Date: 23 Jan 2008

Abstract: We present results obtained by scattering a scalar field off the curved background of a coalescing binary black hole system. A massless scalar field is evolved on a set of fixed backgrounds, each provided by a spatial hypersurface generated numerically during a binary black hole merger. We show that the scalar field scattered from the merger region exhibits quasinormal ringing once a common apparent horizon surrounds the two black holes. This occurs earlier than the onset of the perturbative regime as measured by the start of the quasinormal ringing in the gravitational waveforms. We also use the scalar quasinormal frequencies to associate a mass and a spin with each hypersurface, and observe the compatibility of this measure with the horizon mass and spin computed from the dynamical horizon framework.

#### Jan 25, 2008

0801.3478 (/preprints)
2008-01-25, 09:36 

## [0801.3637] Relativistic versus Newtonian orbitography: the Relativistic Motion Integrator (RMI) software. Illustration with the LISA mission

Authors: S. Pireaux (Observatoire Royal de Belgique, Department 1, Brussels, Belgium), B. Chauvineau (Observatoire de la Cote d&#x27;Azur, Department ARTEMIS, Grasse, France)

Date: 23 Jan 2008

Abstract: The Relativistic Motion Integrator (RMI) consists in integrating numerically the EXACT relativistic equations of motion, with respect to the appropriate gravitational metric, instead of Newtonian equations plus relativistic corrections. The aim of the present paper is to validate the method, and to illustrate how RMI can be used for space missions to produce relativistic ephemerides of satellites. Indeed, nowadays, relativistic effects have to be taken into account, and comparing a RMI ephemeris with a classical keplerian one helps to quantify such effects.
LISA is a relevant example to use RMI. This mission is an interferometer formed by three spacecraft which aims at the detection of gravitational waves. Precise ephemerides of LISA spacecraft are needed not only for the sake of the orbitography but also to compute the photon flight time in laser links between spacecraft, required in LISA data pre-processing in order to reach the gravitational wave detection level.
Relativistic effects in LISA orbitography needed to be considered and quantified. Using RMI, we show that the numerical classical model for LISA orbits in the gravitational field of a non-rotating spherical Sun without planets can be wrong, with respect to the numerical relativisitic version of the same model, by as much as about 9 km in radial distance during a year and up to 59 km in along track distance after a year… with consequences on estimated photon flight times.
We validated RMI numerical results with an analytical developpement. Finally, the RMI relativistic numerical approach is soon more efficient than the analytical development. Moreover, RMI can be applied to other space missions.

#### Jan 25, 2008

0801.3637 (/preprints)
2008-01-25, 09:36 

## [0801.3407] Tests of general relativity in the solar system

Authors: Serge Reynaud, Marc-Thierry Jaekel

Date: 22 Jan 2008

Abstract: Tests of gravity performed in the solar system show a good agreement with general relativity. The latter is however challenged by observations at larger, galactic and cosmic, scales which are presently cured by introducing ‘dark matter’ or ‘dark energy’. A few measurements in the solar system, particularly the so-called ‘Pioneer anomaly’, might also be pointing at a modification of gravity law at ranges of the order of the size of the solar system. The present lecture notes discuss the current status of tests of general relativity in the solar system. They describe metric extensions of general relativity which have the capability to preserve compatibility with existing gravity tests while opening free space for new phenomena. They present arguments for new mission designs and new space technologies as well as for having a new look on data of existing or future experiments.

#### Jan 22, 2008

0801.3407 (/preprints)
2008-01-22, 19:10 

## [0801.3429] Searching for stochastic gravitational-wave background with the co-located LIGO interferometers

Authors: Nickolas V Fotopoulos, for the LIGO Scientific Collaboration

Date: 22 Jan 2008

Abstract: This paper presents techniques developed by the LIGO Scientific Collaboration to search for the stochastic gravitational-wave background using the co-located pair of LIGO interferometers at Hanford, WA. We use correlations between interferometers and environment monitoring instruments, as well as time-shifts between two interferometers (described here for the first time) to identify correlated noise from non-gravitational sources. We veto particularly noisy frequency bands and assess the level of residual non-gravitational coupling that exists in the surviving data.

#### Jan 22, 2008

0801.3429 (/preprints)
2008-01-22, 19:10 

## [0801.2911] Tidal imprint on the gravitational signal emitted by BH-NS coalescing binaries

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

Date: 18 Jan 2008

Abstract: We compute the gravitational signal emitted in the latest phases of the coalescence of a binary system composed of a stellar mass black hole and a neutron star, prior to merging. Tidal interactions are taken into account by means of the affine model approach, in which the neutron star is viewed as a deformable ellipsoid. We compare the orbital and the tidal contributions to the signal, assuming that the star moves in a region where, although very close to the black hole, it has not been disrupted yet. We show that during the last revolutions the star is a non-spherical oscillating object. Indeed, the non-radial oscillations of the star are excited and produce a multiple peak structure in the emitted signal, due to mode coupling, and to the coupling between orbital motion and tidal interaction. This model could be a useful tool to provide reliable initial conditions for numerical relativity simulations of merging processes.

#### Jan 21, 2008

0801.2911 (/preprints)
2008-01-21, 17:54 

## [0712.2460] Fully General Relativistic Simulations of Black Hole-Neutron Star Mergers

Authors: Zachariah B. Etienne, Joshua A. Faber, Yuk Tung Liu, Stuart L. Shapiro, Keisuke Taniguchi, Thomas W. Baumgarte

Date: 14 Dec 2007

Abstract: Black hole-neutron star (BHNS) binaries are expected to be among the leading sources of gravitational waves observable by ground-based detectors, and may be the progenitors of short-hard gamma ray bursts (SGRBs) as well. Here, we discuss our new fully general relativistic calculations of merging BHNS binaries, which use high-accuracy, low-eccentricity, conformal thin-sandwich configurations as initial data. Our evolutions are performed using the moving puncture method and include a fully relativistic, high-resolution shock-capturing hydrodynamics treatment. Focusing on systems in which the neutron star is irrotational and the black hole is nonspinning with a 3:1 mass ratio, we investigate the inspiral, merger, and disk formation in the system. We find that the vast majority of material is promptly accreted and no more than 3% of the neutron star's rest mass is ejected into a tenuous, gravitationally bound disk. We find similar results for mass ratios of 2:1 and 1:1, even when we reduce the NS compaction in the 2:1 mass ratio case. These ambient disks reach temperatures suitable for triggering SGRBs, but their masses may be too small to produce the required total energy output. We measure gravitational waveforms and compute the effective strain in frequency space, finding measurable differences between our waveforms and those produced by binary black hole mergers within the advanced LIGO band. These differences appear at frequencies corresponding to the emission that occurs when the NS is tidally disrupted and accreted by the black hole. The resulting information about the radius of the neutron star may be used to constrain the neutron star equation of state.

#### Jan 21, 2008

0712.2460 (/preprints)
2008-01-21, 17:54 

## [0801.3142] Generating Initial Data in General Relativity using Adaptive Finite Element Methods

Authors: Burak Aksoylu, David Bernstein, Stephen Bond, Michael Holst

Date: 21 Jan 2008

Abstract: The conformal formulation of the Einstein constraint equations is first reviewed, and we then consider the design, analysis, and implementation of adaptive multilevel finite element-type numerical methods for the resulting coupled nonlinear elliptic system. We derive weak formulations of the coupled constraints, and review some new developments in the solution theory for the constraints in the cases of constant mean extrinsic curvature (CMC) data, near-CMC data, and arbitrarily prescribed mean extrinsic curvature data. We then outline some recent results on a priori and a posteriori error estimates for a broad class of Galerkin-type approximation methods for this system which includes techniques such as finite element, wavelet, and spectral methods. We then use these estimates to construct an adaptive finite element method (AFEM) for solving this system numerically, and outline some new convergence and optimality results. We then describe in some detail an implementation of the methods using the FETK software package, which is an adaptive multilevel finite element code designed to solve nonlinear elliptic and parabolic systems on Riemannian manifolds. We finish by describing a simplex mesh generation algorithm for compact binary objects, and then look at a detailed example showing the use of FETK for numerical solution of the constraints.

#### Jan 21, 2008

0801.3142 (/preprints)
2008-01-21, 17:53 

## [0801.2896] Bounds on gravitational wave backgrounds from large distance clock comparisons

Authors: Serge Reynaud, Brahim Lamine, Loic Duchayne, Peter Wolf, Marc-Thierry Jaekel

Date: 18 Jan 2008

Abstract: Our spacetime is filled with gravitational wave backgrounds that constitute a fluctuating environment created by astrophysical and cosmological sources. Bounds on these backgrounds are obtained from cosmological and astrophysical data but also by analysis of ranging and Doppler signals from distant spacecraft. We propose here a new way to set bounds on those backgrounds by performing clock comparisons between a ground clock and a remote spacecraft equipped with an ultra-stable clock, rather than only ranging to an onboard transponder. This technique can then be optimized as a function of the signal to be measured and the dominant noise sources, leading to significant improvements on present bounds in a promising frequency range where different theoretical models are competing. We illustrate our approach using the SAGAS project which aims to fly an ultra stable optical clock in the outer solar system.

#### Jan 21, 2008

0801.2896 (/preprints)
2008-01-21, 10:03 

## [0705.4287] Eccentric double white dwarfs as LISA sources in globular clusters

Authors: B. Willems (1), V. Kalogera (1), A. Vecchio (1,2), N. Ivanova (3), F.A. Rasio (1), J.M. Fregeau (1), K. Belczynski (4) ((1) Northwestern U., (2) U. of Birmingham, (3) U. of Toronto, (4) New Mexico State U.)

Date: 29 May 2007

Abstract: We consider the formation of double white dwarfs (DWDs) through dynamical interactions in globular clusters. Such interactions can give rise to eccentric DWDs, in contrast to the exclusively circular population expected to form in the Galactic disk. We show that for a 5-year Laser Interferometer Space Antenna (LISA) mission and distances as far as the Large Magellanic Cloud, multiple harmonics from eccentric DWDs can be detected at a signal-to-noise ratio higher than 8 for at least a handful of eccentric DWDs, given their formation rate and typical lifetimes estimated from current cluster simulations. Consequently the association of eccentricity with stellar-mass LISA sources does not uniquely involve neutron stars, as is usually assumed. Due to the difficulty of detecting (eccentric) DWDs with present and planned electromagnetic observatories, LISA could provide unique dynamical identifications of these systems in globular clusters.

#### Jan 17, 2008

0705.4287 (/preprints)
2008-01-17, 18:18 

## [0706.3700] Probing white dwarf interiors with LISA: periastron precession in double white dwarfs

Authors: B. Willems (1), A. Vecchio (1,2), V. Kalogera (1) ((1) Northwestern U., (2) U. of Birmingham)

Date: 25 Jun 2007

Abstract: In globular clusters, dynamical interactions give rise to a population of eccentric double white dwarfs detectable by the Laser Interferometer Space Antenna (LISA) up to the Large Magellanic Cloud. In this Letter, we explore the detectability of periastron precession in these systems with LISA. Unlike previous investigations, we consider contributions due to tidal and rotational distortions of the binary components in addition to general relativistic contributions to the periastron precession. At orbital frequencies above a few mHz, we find that tides and stellar rotation dominate, opening up a possibly unique window to the study of the interior and structure of white dwarfs.

#### Jan 17, 2008

0706.3700 (/preprints)
2008-01-17, 18:17 

## [0801.2090] Dynamical excitation of space-time modes of compact objects

Authors: Sebastiano Bernuzzi, Alessandro Nagar, Roberto De Pietri

Date: 14 Jan 2008

Abstract: We discuss, in the perturbative regime, the scattering of Gaussian pulses of odd-parity gravitational radiation off a non-rotating relativistic stars and a Schwarzschild Black Hole. We focus on the excitation of the $w$-modes of the star as a function of the width $b$ of the pulse and we contrast it with the outcome of a Schwarzschild Black Hole of the same mass. For sufficiently narrow values of $b$, the waveforms are dominated by characteristic space-time modes. On the other hand, for sufficiently large values of $b$ the backscattered signal is dominated by the tail of the Regge-Wheeler potential, the quasi-normal modes are not excited and the nature of the central object cannot be established. We view this work as a useful contribution to the comparison between perturbative results and forthcoming $w$-mode 3D-nonlinear numerical simulation.

#### Jan 14, 2008

0801.2090 (/preprints)
2008-01-14, 21:39 

## [0708.0628] Observable Properties of Orbits in Exact Bumpy Spacetimes

Authors: Jonathan R Gair, Chao Li, Ilya Mandel

Date: 4 Aug 2007

Abstract: We explore the properties of test-particle orbits in "bumpy" spacetimes - stationary, reflection-symmetric, asymptotically flat solutions of Einstein equations that have a non-Kerr (anomalous) higher-order multipole-moment structure but can be tuned arbitrarily close to the Kerr metric. Future detectors should observe gravitational waves generated during inspirals of compact objects into supermassive central bodies. If the central body deviates from the Kerr metric, this will manifest itself in the emitted waves. Here, we explore some of the features of orbits in non-Kerr spacetimes that might lead to observable signatures. As a basis for this analysis, we use a family of exact solutions proposed by Manko & Novikov which deviate from the Kerr metric in the quadrupole and higher moments, but we also compare our results to other work in the literature. We examine isolating integrals of the orbits and find that the majority of geodesic orbits have an approximate fourth constant of the motion (in addition to the energy, angular momentum and rest mass) and the resulting orbits are tri-periodic to high precision. We also find that this fourth integral can be lost for certain orbits in some oblately deformed Manko-Novikov spacetimes. However, compact objects will probably not end up on these chaotic orbits in nature. We compute the location of the innermost stable circular orbit (ISCO) and find that the behavior of orbtis near the ISCO can be qualitatively different depending on whether the ISCO is determined by the onset of an instability in the radial or vertical direction. Finally, we compute periapsis and orbital-plane precessions for nearly circular and nearly equatorial orbits in both the strong and weak field, and discuss weak-field precessions for eccentric equatorial orbits.

#### Jan 14, 2008

0708.0628 (/preprints)
2008-01-14, 21:37 

## [0801.0739] Prompt Shocks in the Gas Disk Around a Recoiling Supermassive Black Hole Binary

Authors: Zoltan Lippai (1), Zsolt Frei (1), Zoltan Haiman (2) ((1) Inst. of Physics, Eotvos University, Budapest, Hungary, (2) Dept. of Astronomy, Columbia University, New York, NY)

Date: 7 Jan 2008

Abstract: Supermassive black hole binaries (BHBs) produced in galaxy mergers recoil at the time of their coalescence due to the emission of gravitational waves (GWs). We simulate the response of a thin, 2D disk of collisionless particles, initially on circular orbits around a 10ˆ6 M_sun BHB, to kicks that are either parallel or perpendicular to the initial orbital plane. Typical kick velocities (v_k) can exceed the sound speed in a circumbinary gas disk. While the inner disk is strongly bound to the recoiling binary, the outer disk is only weakly bound or unbound. This leads to differential motions in the disturbed disk that increase with radius and can become supersonic at ~700 Schwarzschild radii for v_k ~500 km/s, implying that shocks form beyond this radius. We indeed find that kicks in the disk plane lead to immediate strong density enhancements (within weeks) in a tightly wound spiral caustic, propagating outward at the speed v_k. Concentric density enhancements are also observed for kicks perpendicular to the disk, but are weaker and develop into caustics only after a long delay (>1 year). Unless both BH spins are low or precisely aligned with the orbital angular momentum, a significant fraction (> several %) of kicks are sufficiently large and well aligned with the orbital plane for strong shocks to be produced. The shocks could result in an afterglow whose characteristic photon energy increases with time, from the UV (~10eV) to the soft X-ray (~100eV) range, between one month and one year after the merger. This could help identify EM counterparts to GW sources discovered by LISA.

#### Jan 10, 2008

0801.0739 (/preprints)
2008-01-10, 17:41 

## [0801.1528] Acceleration and Classical Electromagnetic Radiation

Authors: E.N. Glass

Date: 9 Jan 2008

Abstract: Classical radiation from an accelerated charge is reviewed along with the reciprocal topic of accelerated observers detecting radiation from a static charge. This review commemerates Bahram Mashhoon's 60th birthday.

#### Jan 10, 2008

0801.1528 (/preprints)
2008-01-10, 17:40 

## [0708.0001] The effects of Chern-Simons gravity on bodies orbiting the Earth

Authors: Tristan L. Smith (Caltech), Adrienne L. Erickcek (Caltech), Robert R. Caldwell (Dartmouth College), Marc Kamionkowski (Caltech)

Date: 31 Jul 2007

Abstract: One of the possible low-energy consequences of string theory is the addition of a Chern-Simons term to the standard Einstein-Hilbert action of general relativity. It can be argued that the quintessence field should couple to this Chern-Simons term, and if so, it drives in the linearized theory a parity-violating interaction between the gravito-electric and gravitomagnetic fields. In this paper, the linearized spacetime for Chern-Simons gravity around a massive spinning body is found to include new modifications to the gravitomagnetic field that have not appeared in previous work. The orbits of test bodies and the precession of gyroscopes in this spacetime are calculated, leading to new constraints on the Chern-Simons parameter space due to current satellite experiments.

#### Jan 09, 2008

0708.0001 (/preprints)
2008-01-09, 23:49 

## [0801.0900] Self-force on extreme mass ratio inspirals via curved spacetime effective field theory

Authors: Chad R. Galley, B. L. Hu

Date: 7 Jan 2008

Abstract: We construct an effective field theory (EFT) to derive the self-force on a compact object moving in the background spacetime of a supermassive black hole. The EFT approach utilizes the disparity between two length scales, the size of the compact object $r_m$ and the radius of curvature of the background spacetime $\cR$ such that $\mu \equiv r_m / \cR \ll 1$, to treat the orbital dynamics of the compact object, described as an effective point particle, separately from its tidal deformations. The equation of motion of an effective relativistic point particle coupled to the gravitational waves generated by its motion in a curved background spacetime can be derived without making a slow motion or weak field approximation, as was assumed in earlier EFT treatment of post-Newtonian binaries. Ultraviolet divergences are regularized using Hadamard's {\it partie finie} to isolate the non-local finite part from the quasi-local divergent part. The latter is constructed from a momentum space representation for the graviton retarded propagator and is evaluated using dimensional regularization in which only logarithmic divergences are relevant for renormalizing the parameters of the theory. As an important application of this framework we explicitly derive the first order self-force given by Mino, Sasaki, Tanaka, Quinn and Wald. Going beyond the point particle approximation, to account for the finite size of the object, we demonstrate that for extreme mass ratio inspirals the motion of a compact object is affected by tidally induced moments at $O(\muˆ4)$, in the form of an Effacement Principle. This work provides a new foundation for further exploration of higher order self force corrections, gravitational radiation and spinning compact objects.

#### Jan 07, 2008

0801.0900 (/preprints)
2008-01-07, 20:02 

## [0708.2720] Simulating binary neutron stars: dynamics and gravitational waves

Authors: Matthew Anderson, Eric W. Hirschmann, Luis Lehner, Steven L. Liebling, Patrick M. Motl, David Neilsen, Carlos Palenzuela, Joel E. Tohline

Date: 20 Aug 2007

Abstract: We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the \had computational infrastructure for distributed adaptive mesh refinement.

#### Jan 07, 2008

0708.2720 (/preprints)
2008-01-07, 12:02 

## [astro-ph/0701629] Pre-Merger Localization of Gravitational-Wave Standard Sirens With LISA

Authors: Bence Kocsis (1,2), Zolt&#xe1;n Haiman (3), Kristen Menou (3), Zsolt Frei (1) ((1) Eotvos, (2) CFA, (3) Columbia)

Date: 23 Jan 2007

Abstract: The continuous improvement in localization errors (sky position and distance) in real time as LISA observes the gradual inspiral of a supermassive black hole (SMBH) binary can be of great help in identifying any prompt electromagnetic counterpart associated with the merger. We develop a new method, based on a Fourier decomposition of the time-dependent, LISA-modulated gravitational-wave signal, to study this intricate problem. The method is faster than standard Monte Carlo simulations by orders of magnitude. By surveying the parameter space of potential LISA sources, we find that counterparts to SMBH binary mergers with total mass M~10ˆ5-10ˆ7 M_Sun and redshifts z<~3 can be localized to within the field of view of astronomical instruments (~degˆ2) typically hours to weeks prior to coalescence. This will allow targeted searches for variable electromagnetic counterparts as the merger proceeds, as well as monitoring of the most energetic coalescence phase. A rich set of astrophysical and cosmological applications would emerge from the identification of electromagnetic counterparts to these gravitational-wave standard sirens.

#### Jan 03, 2008

0701629 (/preprints/astro-ph)
2008-01-03, 15:37 

## [0709.0003] Probing Gravity with Spacetime Sirens

Authors: Cedric Deffayet (APC/IAP), Kristen Menou (Columbia)

Date: 31 Aug 2007

Abstract: A gravitational observatory such as LISA will detect coalescing pairs of massive black holes, accurately measure their luminosity distance and help identify a host galaxy or an electromagnetic counterpart. If dark energy is a manifestation of modified gravity on large scales, gravitational waves from cosmologically-distant spacetime sirens are direct probes of this new physics. For example, a gravitational Hubble diagram based on black hole pair luminosity distances and host galaxy redshifts could reveal a large distance extra-dimensional leakage of gravity. Various additional signatures may be expected in a gravitational signal propagated over cosmological scales.

#### Jan 03, 2008

0709.0003 (/preprints)
2008-01-03, 15:36 

## [0712.0618] Precision of Hubble constant derived using black hole binary absolute

Authors: Chelsea L. MacLeod, Craig J. Hogan

Date: 4 Dec 2007

Abstract: Measured gravitational waveforms from black hole binary inspiral events directly determine absolute luminosity distances. To use these data for cosmology, it is necessary to independently obtain redshifts for the events, which may be difficult for those without electromagnetic counterparts. Here it is demonstrated that certainly in principle, and possibly in practice, clustering of galaxies allows extraction of the redshift information from a sample statistically for the purpose of estimating mean cosmological parameters, without identification of host galaxies for individual events. We extract mock galaxy samples from the 6th Data Release of the Sloan Digital Sky Survey resembling those that would be associated with inspiral events of stellar mass black holes falling into massive black holes at redshift z ~ 0.1 to 0.5. A simple statistical procedure is described to estimate a likelihood function for the Hubble constant H_0: each galaxy in a LISA error volume contributes linearly to the log likelihood for the source redshift, and the log likelihood for each source contributes linearly to that of H_0. This procedure is shown to provide an accurate and unbiased estimator of H_0. It is estimated that a precision better than one percent in H_0 may be possible if the rate of such events is sufficiently high, on the order of 20 to z = 0.5.

#### Jan 03, 2008

0712.0618 (/preprints)
2008-01-03, 15:35 

## [0708.2144] Some Applications of Ricci Flow in Physics

Authors: E. Woolgar

Date: 16 Aug 2007

Abstract: I discuss certain applications of the Ricci flow in physics. I first review how it arises in the renormalization group (RG) flow of a nonlinear sigma model. I then review the concept of a Ricci soliton and recall how a soliton was used to discuss the RG flow of mass in 2-dimensions. I then present recent results obtained with Oliynyk on the flow of mass in higher dimensions. The final section discusses one way in which Ricci flow may arise in general relativity, particularly for static metrics.

#### Jan 02, 2008

0708.2144 (/preprints)
2008-01-02, 19:28 

## [0711.1677] Testing the general relativistic ''no-hair'' theorems using the galactic

Authors: Clifford M. Will (Washington University, St. Louis)

Date: 11 Nov 2007

Abstract: If a class of stars orbits the central black hole in our galaxy in short period (~ 0.1 year), high eccentricity (~ 0.9) orbits, they will experience precessions of their orbital planes induced by both relativistic frame-dragging and the quadrupolar gravity of the hole, at levels that could be as large as 10 microarcseconds per year, if the black hole is rotating faster than ½ of its maximum rotation rate. Astrometric observations of the orbits of at least two such stars can in principle lead to a determination of the angular momentum vector J of the black hole and its quadrupole moment Q_2. This could lead to a test of the general relativistic no-hair theorems, which demand that Q_2 = - Jˆ2/M. Future high-precision adaptive infrared optics instruments make make such a fundamental test of the black-hole paradigm possible.

#### Jan 02, 2008

0711.1677 (/preprints)
2008-01-02, 19:28 

## [0801.0122] Gravitational waves from hyperbolic encounters

Authors: S. Capozziello, M. De Laurentis, F.De Paolis, G. Ingrosso, A. Nucita

Date: 30 Dec 2007

Abstract: The emission of gravitational waves from a system of massive objects interacting on hyperbolic orbits is studied in the quadrupole approximation. Analytic expressions are derived for the gravitational radiation luminosity, the total energy output and the gravitational radiation amplitude. An estimation of the expected number of events towards different targets (i.e. globular clusters and the center of the Galaxy) is also given. In particular, for a dense stellar cluster at the galactic center, a rate up to one event per year is obtained.

#### Jan 02, 2008

0801.0122 (/preprints)
2008-01-02, 19:27 

## [0712.4363] Applications of distance between probability distributions to gravitational wave data analysis

Authors: Robert J. Budzy&#x144;ski, Witold Kondracki, Andrzej Kr&#xf3;lak

Date: 28 Dec 2007

Abstract: We present a definition of the distance between probability distributions. Our definition is based on the $L_1$ norm on space of probability measures. We compare our distance with the well-known Kullback-Leibler divergence and with the proper distance defined using the Fisher matrix as a metric on the parameter space. We consider using our notion of distance in several problems in gravitational wave data analysis: to place templates in the parameter space in searches for gravitational-wave signals, to assess quality of search templates, and to study the signal resolution.

#### Jan 02, 2008

0712.4363 (/preprints)
2008-01-02, 09:35