## [gr-qc/0511157] Relativistic analysis of the LISA long range optical links

Authors: Bertrand Chauvineau, Sophie Pireaux, Tania Regimbau, Jean-Yves Vinet

Date: Tue, 29 Nov 2005

Abstract: The joint ESA/NASA LISA mission consists in three spacecraft on heliocentric orbits, flying in a triangular formation of 5 Mkm each side, linked by infrared optical beams. The aim of the mission is to detect gravitational waves in a low frequency band. For properly processing the science data, the propagation delays between spacecraft must be accurately known. We thus analyse the propagation of light between spacecraft in order to systematically derive the relativistic effects due to the static curvature of the Schwarzschild spacetime in which the spacecraft are orbiting with time-varying light-distances. In particular, our analysis allows to evaluate rigorously the Sagnac effect, and the gravitational (Einstein) redshift.

#### Nov 30, 2005

0511157 (/preprints/gr-qc)
2005-11-30, 11:27 

## [gr-qc/0511145] Detecting a gravitational-wave background with next-generation space interferometers

Authors: Hideaki Kudoh, Atsushi Taruya, Takashi Hiramatsu, Yoshiaki Himemoto

Date: Sun, 27 Nov 2005

Abstract: Future missions of gravitational-wave astronomy will be operated by space-based interferometers, covering very wide range of frequency band. Search for stochastic gravitational-wave backgrounds (GWBs) is one of the main target for such missions, and we here discuss the prospects for direct measurement of isotropic and anisotropic components of (primordial) GWBs around the frequency 0.1-10 Hz. After extending the theoretical basis for correlation analysis, we evaluate the sensitivity and the signal-to-noise ratio for the proposed future missions of space interferometers, like Big-Bang Observer (BBO), Deci-Hertz Interferometer Gravitational-wave Observer (DECIGO) and recently proposed Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at the low frequency may be a big obstacle and significantly reduce the signal-to-noise ratio of GWBs. As a result, minimum detectable amplitude may reach hˆ2 \Omega = 10ˆ{-15} - 10ˆ{-16}, as long as foreground point sources are properly subtracted. Based on the correlation analysis, we also discuss measurement of anisotropies of GWBs. As an example, sensitivity level required for detecting the dipole moment of GWB induced by the proper motion of our local system is closely examined.

#### Nov 28, 2005

0511145 (/preprints/gr-qc)
2005-11-28, 20:55 

## [astro-ph/0511517] Amplitude and Phase Fluctuations for Gravitational Waves Propagating through Inhomogeneous Mass Distribution in the Universe

Authors: Ryuichi Takahashi

Date: Thu, 17 Nov 2005

Abstract: When a gravitational wave (GW) from a distant source propagates through the universe, its amplitude and phase change due to gravitational lensing by the inhomogeneous mass distribution. We derive the amplitude and phase fluctuations, and calculate these variances in the limit of a weak gravitational field of density perturbation. If the scale of the perturbation is smaller than the Fresnel scale $\sim 100 {pc} (f/{mHz})ˆ{-½}$ ($f$ is the GW frequency), the GW is not magnified due to the diffraction effect. The rms amplitude fluctuation is $1-10 %$ for $f > 10ˆ{-10}$ Hz, but it is reduced less than 5% for a very low frequency of $f < 10ˆ{-12}$ Hz. The rms phase fluctuation in the chirp signal is $\sim 10ˆ{-3}$ radian at LISA frequency band ($10ˆ{-5} - 10ˆ{-1}$ Hz). Measurements of these fluctuations will provide information about the matter power spectrum on the Fresnel scale $\sim 100$ pc.

#### Nov 21, 2005

0511517 (/preprints/astro-ph)
2005-11-21, 21:39 

## [hep-ph/0511217] Trust but verify: The case for astrophysical black holes

Authors: Scott A. Hughes

Date: Thu, 17 Nov 2005

Abstract: This article is based on a pair of lectures given at the 2005 SLAC Summer Institute. Our goal is to motivate why most physicists and astrophysicists accept the hypothesis that the most massive, compact objects seen in many astrophysical systems are described by the black hole solutions of general relativity. We describe the nature of the most important black hole solutions, the Schwarzschild and the Kerr solutions. We discuss gravitational collapse and stability in order to motivate why such objects are the most likely outcome of realistic astrophysical collapse processes. Finally, we discuss some of the observations which -- so far at least -- are totally consistent with this viewpoint, and describe planned tests and observations which have the potential to falsify the black hole hypothesis, or sharpen still further the consistency of data with theory.

#### Nov 20, 2005

0511217 (/preprints/hep-ph)
2005-11-20, 22:43 

## [gr-qc/0511103] Gravitational wave extraction from an inspiraling configuration of merging black holes

Authors: John G. Baker, Joan Centrella, Dae-Il Choi, Michael Koppitz, James van Meter

Date: Thu, 17 Nov 2005

Abstract: We present new techniqes for evolving binary black hole systems which allow the accurate determination of gravitational waveforms directly from the wave zone region of the numerical simulations. Rather than excising the black hole interiors, our approach follows the "puncture" treatment of black holes, but utilzing a new gauge condition which allows the black holes to move successfully through the computational domain. We apply these techniques to an inspiraling binary, modeling the radiation generated during the final plunge and ringdown. We demonstrate convergence of the waveforms and good conservation of mass-energy, with just over 3% of the system's mass converted to gravitional radiation.

#### Nov 17, 2005

0511103 (/preprints/gr-qc)
2005-11-17, 22:36 

## [astro-ph/0511254] The Local Rate and the Progenitor Lifetime of Short-Hard Gamma-Ray Bursts: Synthesis and Predictions for LIGO

Authors: Ehud Nakar, Avishay Gal-Yam, Derek B. Fox

Date: Wed, 9 Nov 2005

Abstract: The properties of the short-hard gamma-ray bursts (SHBs) with known host-galaxies suggest that these events result from a long-lived progenitor system. The most popular progenitor model of SHBs invokes the merger of either double neutron star (DNS) binaries or neutron star-black hole (NS-BH) systems. Such events produce strong gravitational waves (GWs) at frequency range that is accessible to current and next-generation ground-based GW observatories. In this work we combine the census of SHB observations with refined theoretical analysis to critically evaluate the compact binary progenitor model. We then explore the implications for GW detection of these events. Beginning from the measured star-formation rate through cosmic time, we consider what intrinsic luminosity and lifetime distributions can reproduce both the known SHB redshifts and luminosities, and the peak flux distribution of the large BATSE SHB sample. We find that (1) Short progenitor lifetimes, <3 Gyr, are ruled out, and lifetimes of about 6 Gyr favored. This result is difficult to reconcile with the observed properties of the DNS population in our galaxy. We show that for DNS systems to remain viable SHB progenitors, a large population of old undetectable NS binaries must be postulated. (2) We find that the local rate of SHBs is at least 10 Gpcˆ-3 yrˆ-1 and likely as high as 10ˆ5 Gpcˆ-3 yr-1, significantly above earlier estimates. (3) We find that assuming that SHBs do result from compact binaries, either through the old DNS population mentioned above or from NS-BH mergers, our resulting predictions for the LIGO event rate are extremely encouraging: several detections per year may be expected at design sensitivity, and the first coincident observation of electromagnetic and gravitational radiation from an SHB may well be made with current facilities.

#### Nov 17, 2005

0511254 (/preprints/astro-ph)
2005-11-17, 10:50 

## [gr-qc/0511092] BBO and the Neutron-Star-Binary Subtraction Problem

Authors: C. Cutler, J. Harms

Date: Wed, 16 Nov 2005

Abstract: The Big Bang Observer (BBO) is a proposed space-based gravitational-wave (GW) mission designed primarily to search for an inflation-generated GW background in the frequency range 0.1-1 Hz. The major astrophysical foreground in this range is gravitational radiation from inspiraling compact binaries. This foreground is expected to be much larger than the inflation-generated background, so to accomplish its main goal, BBO must be sensitive enough to identify and subtract out practically all such binaries in the observable universe. It is somewhat subtle to decide whether BBO's current baseline design is sufficiently sensitive for this task, since, at least initially, the dominant noise source impeding identification of any one binary is confusion noise from all the others. Here we present a self-consistent scheme for deciding whether BBO's baseline design is indeed adequate for subtracting out the binary foreground. We conclude that the current baseline should be sufficient. However if BBO's instrumental sensitivity were degraded by a factor 2-4, it could no longer perform its main mission. It is impossible to perfectly subtract out each of the binary inspiral waveforms, so an important question is how to deal with the "residual" errors in the post-subtraction data stream. We sketch a strategy of "projecting out" these residual errors, at the cost of some effective bandwidth. We also provide estimates of the sizes of various post-Newtonian effects in the inspiral waveforms that must be accounted for in the BBO analysis.

#### Nov 17, 2005

0511092 (/preprints/gr-qc)
2005-11-17, 10:47 

## [gr-qc/0506124] Active laser frequency stabilization and resolution enhancement of interferometers for the measurement of gravitational waves in space

Authors: Markus Herz

Date: Tue, 23 Aug 2005

Abstract: Laser frequency stabilization is notably one of the major challenges on the way to a space-borne gravitational wave observatory. The proposed Laser Interferometer Space Antenna (LISA) is presently under development in an ESA, NASA collaboration. We present a novel method for active laser stabilization and phase noise suppression in such a gravitational wave detector. The proposed approach is a further evolution of the "arm locking" method, which in essence consists of using an interferometer arm as an optical cavity, exploiting the extreme long-run stability of the cavity size in the frequency band of interest. We extend this method by using the natural interferometer arm length differences and existing interferometer signals as additional information sources for the reconstruction and active suppression of the quasi-periodic laser frequency noise, enhancing the resolution power of space-borne gravitational wave detectors.

#### Nov 16, 2005

0506124 (/preprints/gr-qc)
2005-11-16, 08:50 

## [astro-ph/0511366] The Dynamical Evolution of Black Hole-Neutron Star Binaries in General Relativity: Simulations of Tidal Disruption

Authors: Joshua A. Faber, Thomas W. Baumgarte, Stuart L. Shapiro, Keisuke Taniguchi, Frederic A. Rasio

Date: Fri, 11 Nov 2005

Abstract: We calculate the first dynamical evolutions of merging black hole-neutron star binaries that construct the combined black hole-neutron star spacetime in a general relativistic framework. We treat the metric in the conformal flatness approximation, and assume that the black hole mass is sufficiently large compared to that of the neutron star so that the black hole remains fixed in space. Using a spheroidal spectral methods solver, we solve the resulting field equations for a neutron star orbiting a Schwarzschild black hole. The matter is evolved using a relativistic, Lagrangian, smoothed particle hydrodynamics (SPH) treatment. We take as our initial data recent quasiequilibrium models for synchronized neutron star polytropes generated as solutions of the conformal thin-sandwich (CTS) decomposition of the Einstein field equations. We are able to construct from these models relaxed SPH configurations whose profiles show good agreement with CTS solutions. Our adiabatic evolution calculations for neutron stars with low compactness show that mass transfer, when it begins while the neutron star orbit is still outside the innermost stable circular orbit, is more unstable than is typically predicted by analytical formalisms. This dynamical mass loss is found to be the driving force in determining the subsequent evolution of the binary orbit and the neutron star, which typically disrupts completely within a few orbital periods. The majority of the mass transferred onto the black hole is accreted promptly; a significant fraction (~30%) of the mass is shed outward as well, some of which will become gravitationally unbound and ejected completely from the system. The remaining portion forms an accretion disk around the black hole, and could provide the energy source for short-duration gamma ray bursts.

#### Nov 16, 2005

0511366 (/preprints/astro-ph)
2005-11-16, 08:33 

## [gr-qc/0511073] Teaching General Relativity

Authors: Robert M. Wald

Date: Mon, 14 Nov 2005

Abstract: This Resource Letter provides some guidance on issues that arise in teaching general relativity at both the undergraduate and graduate levels. Particular emphasis is placed on strategies for presenting the mathematical material needed for the formulation of general relativity.

#### Nov 15, 2005

0511073 (/preprints/gr-qc)
2005-11-15, 11:46 

## [gr-qc/0511041] Reference frames and rigid motions in relativity: Applications

Authors: D. Soler

Date: Tue, 8 Nov 2005

Abstract: The concept of rigid reference frame and of constricted spatial metric, given in the previous work [\emph{Clas. Quantum Grav.} {\bf 21}, 3067,(2004)] are here applied to some specific space-times: In particular, the rigid rotating disc with constant angular velocity in Minkowski space-time is analyzed, a new approach to the Ehrenfest paradox is given as well as a new explanation of the Sagnac effect. Finally the anisotropy of the speed of light and its measurable consequences in a reference frame co-moving with the Earth are discussed.

#### Nov 08, 2005

0511041 (/preprints/gr-qc)
2005-11-08, 22:38 

## [gr-qc/0511033] Dynamical evolution and leading order gravitational wave emission of Riemann-S binaries

Authors: Dörte Hansen

Date: Mon, 7 Nov 2005

Abstract: An approximate strategy for studying the evolution of binary systems of extended objects is introduced. The stars are assumed to be polytropic ellipsoids. The surfaces of constant density maintain their ellipsoidal shape during the time evolution. The equations of hydrodynamics then reduce to a system of ordinary differential equations for the internal velocities, the principal axes of the stars and the orbital parameters. The equations of motion are given within Lagrangian and Hamiltonian formalism. The special case when both stars are axially symmetric fluid configurations is considered. Leading order gravitational radiation reaction is incorporated, where the quasi-static approximation is applied to the internal degrees of freedom of the stars. The influence of the stellar parameters, in particular the influence of the polytropic index $n$, on the leading order gravitational waveforms is studied.

#### Nov 08, 2005

0511033 (/preprints/gr-qc)
2005-11-08, 09:30 

## [gr-qc/0511018] The Midpoint Rule as a Variational--Symplectic Integrator. I. Hamiltonian Systems

Authors: David Brown

Date: Thu, 3 Nov 2005

Abstract: Numerical algorithms based on variational and symplectic integrators exhibit special features that make them promising candidates for application to general relativity and other constrained Hamiltonian systems. This paper lays part of the foundation for such applications. The midpoint rule for Hamilton's equations is examined from the perspectives of variational and symplectic integrators. It is shown that the midpoint rule preserves the symplectic form, conserves Noether charges, and exhibits excellent long--term energy behavior. The energy behavior is explained by the result, shown here, that the midpoint rule exactly conserves a phase space function that is close to the Hamiltonian. The presentation includes several examples.

#### Nov 07, 2005

0511018 (/preprints/gr-qc)
2005-11-07, 10:26 

## [gr-qc/0511009] The deterministic nature of conservative post-Newtonian accurate dynamics of compact binaries with leading order spin-orbit interaction

Authors: Achamveedu Gopakumar, Christian Koenigsdoerffer

Date: Wed, 2 Nov 2005

Abstract: We formally show that the conservative second post-Newtonian (PN) accurate dynamics of spinning compact binaries moving in eccentric orbits, when spin effects are restricted to the leading order spin-orbit interaction cannot be chaotic for the following two distinct cases: (i) the binary consists of compact objects of arbitrary mass, where only one of them is spinning with an arbitrary spin and (ii) the binary consists of equal mass compact objects, having two arbitrary spins. We rest our arguments on the recent determination of PN accurate Keplerian-type parametric solutions to the above cases, indicating that the PN accurate dynamics is integrable in these two situations. We compare predictions of our case (i) with those from a numerical investigation of an equivalent scenario that observed chaos in the associated dynamics. We also present possible reasons for the discrepancies.

#### Nov 03, 2005

0511009 (/preprints/gr-qc)
2005-11-03, 10:20 

## [gr-qc/0510129] Improved approximate inspirals of test-bodies into Kerr black holes

Authors: Jonathan R Gair, Kostas Glampedakis

Date: Mon, 31 Oct 2005

Abstract: We present an improved version of the approximate scheme for generating inspirals of test-bodies into a Kerr black hole recently developed by Glampedakis, Hughes and Kennefick. Their original "hybrid" scheme was based on combining exact relativistic expressions for the evolution of the orbital elements (the semi-latus rectum p and eccentricity e) with approximate, weak-field, formula for the energy and angular momentum fluxes, amended by the assumption of constant inclination angle, iota, during the inspiral. Despite the fact that the resulting inspirals were overall well-behaved, certain pathologies remained for orbits in the strong field regime and for orbits which are nearly circular and/or nearly polar. In this paper we eliminate these problems by incorporating an array of improvements in the approximate fluxes. Firstly, we add certain corrections which ensure the correct behaviour of the fluxes in the limit of vanishing eccentricity and/or 90 degrees inclination. Secondly, we use higher order post-Newtonian formulae, adapted for generic orbits. Thirdly, we drop the assumption of constant inclination. Instead, we first evolve the Carter constant by means of an approximate post-Newtonian expression and subsequently extract the evolution of iota. Finally, we improve the evolution of circular orbits by using fits to the angular momentum and inclination evolution determined by Teukolsky based calculations. As an application of the improved scheme we provide a sample of generic Kerr inspirals and for the specific case of nearly circular orbits we locate the critical radius where orbits begin to decircularise under radiation reaction. These easy-to-generate inspirals should become a useful tool for exploring LISA data analysis issues and may ultimately play a role in source detection.

#### Nov 01, 2005

0510129 (/preprints/gr-qc)
2005-11-01, 11:25