**Authors**: S. V. Dhurandhar, J-Y. Vinet, K. Rajesh Nayak

**Date**: 28 May 2008

**Abstract**: LISA is a joint space mission of the NASA and the ESA for detecting low frequency gravitational waves in the band $10ˆ{-5} - 1$ Hz. In order to attain the requisite sensitivity for LISA, the laser frequency noise must be suppressed below the other secondary noises such as the optical path noise, acceleration noise etc. This is achieved by combining time-delayed data for which precise knowledge of time-delays is required. The gravitational field, mainly that of the Sun and the motion of LISA affect the time-delays and the optical links. Further, the effect of the gravitational field of the Earth on the orbits of spacecraft is included. This leads to additional flexing over and above that of the Sun. We have written a numerical code which computes the optical links, that is, the time-delays with great accuracy $\sim 10ˆ{-2}$ metres - more than what is required for time delay interferometry (TDI) - for most of the orbit and with sufficient accuracy within $\sim 10$ metres for an integrated time window of about six days, when one of the arms tends to be tangent to the orbit. Our analysis of the optical links is fully general relativistic and the numerical code takes into account effects such as the Sagnac, Shapiro delay, etc.. We show that with the deemed parameters in the design of LISA, there are symmetries inherent in the configuration of LISA and in the physics, which may be used effectively to suppress the residual laser noise in the modified first generation TDI. We demonstrate our results for some important TDI variables.

0805.4314
(/preprints)

2008-05-30, 11:46
**[edit]**

**Authors**: Miroslav Micic, Kelly Holley-Bockelmann, Steinn Sigurdsson

**Date**: 20 May 2008

**Abstract**: (Abridged) We use high resolution cosmological N-body simulations to study the growth of intermediate to supermassive black holes from redshift 49 to zero. We track the growth of black holes from the seeds of population III stars to black holes in the range of 10ˆ3 < M < 10ˆ7 Msun -- not quasars, but rather IMBH to low-mass SMBHs. These lower mass black holes are the primary observable for the Laser Interferometer Space Antenna (LISA). The large-scale dynamics of the black holes are followed accurately within the simulation down to scales of 1 kpc; thereafter, we follow the merger analytically from the last dynamical friction phase to black hole coalescence. We find that the merger rate of these black holes is R~25 per year between 8 < z < 11 and R = 10 per year at z=3. Before the merger occurs the incoming IMBH may be observed with a next generation of X-ray telescopes as a ULX source with a rate of about ~ 3 - 7 per year for 1 < z < 5. We develop an analytic prescription that captures the most important black hole growth mechanisms: galaxy merger-driven gas accretion and black hole coalescence. Using this, we find that SMBH at the center of Milky Way type galaxy was in place with most of its mass by z = 4.7, and most of the growth was driven by gas accretion excited by major mergers. Hundreds of black holes have failed to coalesce with the SMBH by z=0, some with masses of 10000 Msun, orbiting within the dark matter halo with luminosities up to ~ 30000 Lsun. These X-ray sources can easily be observed with Chandra at ~ 100 kpc.

0805.3154
(/preprints)

2008-05-27, 19:10
**[edit]**

**Authors**: Geoffrey Lovelace, Robert Owen, Harald P. Pfeiffer, Tony Chu

**Date**: 27 May 2008

**Abstract**: There is a significant possibility that astrophysical black holes with nearly-extremal spins exist. Numerical simulations of such systems require suitable initial data. In this paper, we examine three methods of constructing binary-black-hole initial data, focusing on their ability to generate black holes with nearly-extremal spins: (i) Bowen-York initial data, including standard puncture data (based on conformal flatness and Bowen-York extrinsic curvature), (ii) standard quasi-equilibrium initial data (based on the extended-conformal-thin-sandwich equations, conformal flatness, and maximal slicing), and (iii) quasi-equilibrium data based on the superposition of Kerr-Schild metrics. We find that the two conformally-flat methods (i) and (ii) perform similarly, with spins up to about 0.99 obtainable at the initial time. However, in an evolution, we expect the spin to quickly relax to a significantly smaller value around 0.93 as the initial geometry relaxes. For quasi-equilibrium superposed Kerr-Schild (SKS) data [method (iii)], we construct initial data with initial spins as large as 0.9998. We evolve SKS data sets with spins of 0.93 and 0.97 and find that the spin drops by only a few parts in $10ˆ4$ during the initial relaxation; therefore, we expect that SKS initial data will allow evolutions of binary black holes with relaxed spins above 0.99. [Abstract abbreviated; full abstract also mentions several secondary results.]

0805.4192
(/preprints)

2008-05-27, 19:10
**[edit]**

**Authors**: Larry R. Price, Xavier Siemens

**Date**: 23 May 2008

**Abstract**: Several mechanisms exist for generating a stochastic background of gravitational waves in the period following inflation. These mechanisms are generally classical in nature, with the gravitational waves being produced from inhomogeneities in the fields that populate the early universe and not quantum fluctuations. The resulting stochastic background could be accessible to next generation gravitational wave detectors. We develop a framework for computing such a background analytically and computationally. As an application of our framework, we consider the stochastic background of gravitational waves generated in a simple model of preheating.

0805.3570
(/preprints)

2008-05-27, 19:09
**[edit]**

**Authors**: Slava G. Turyshev, Benjamin Lane, Michael Shao, Andre Girerd

**Date**: 27 May 2008

**Abstract**: The primary objective of the Beyond Einstein Advanced Coherent Optical Network (BEACON) mission is a search for new physics beyond general relativity by measuring the curvature of relativistic space-time around Earth. This curvature is characterized by the Eddington parameter \gamma -- the most fundamental relativistic gravity parameter and a direct measure for the presence of new physical interactions. BEACON will achieve an accuracy of 1 x 10ˆ{-9} in measuring the parameter \gamma, thereby going a factor of 30,000 beyond the present best result involving the Cassini spacecraft. Secondary mission objectives include: (i) a direct measurement of the "frame-dragging" and geodetic precessions in the Earth's rotational gravitomagnetic field, to 0.05% and 0.03% accuracy correspondingly, (ii) first measurement of gravity's non-linear effects on light and corresponding 2nd order spatial metric's effects to 0.01% accuracy. BEACON will lead to robust advances in tests of fundamental physics -- this mission could discover a violation or extension of general relativity and/or reveal the presence of an additional long range interaction in physics. BEACON will provide crucial information to separate modern scalar-tensor theories of gravity from general relativity, probe possible ways for gravity quantization, and test modern theories of cosmological evolution.

0805.4033
(/preprints)

2008-05-27, 19:09
**[edit]**

**Authors**: Demetrios Christodoulou

**Date**: 26 May 2008

**Abstract**: The subject of this work is the formation of black holes in pure general relativity, by the focusing of incoming gravitational waves. The theorems established in this monograph constitute the first foray into the long time dynamics of general relativity in the large, that is, when the initial data are no longer confined to a suitably small neighborhood of Minkowskian data. The theorems are general, no symmetry conditions on the initial data being imposed.

0805.3880
(/preprints)

2008-05-27, 19:09
**[edit]**

**Authors**: D. Baskaran, A. G. Polnarev, M. S. Pshirkov, K. A. Postnov

**Date**: 20 May 2008

**Abstract**: In this work, analyzing the propagation of electromagnetic waves in the field of gravitational waves, we show the presence and significance of the so called surfing effect for pulsar timing measurements. It is shown that, due to the transverse nature of gravitational waves, the surfing effect leads to enormous pulsar timing residuals if the speed of gravitational waves is smaller than speed of light. This fact allows to place significant constraints on parameter $\epsilon$, which characterizes the relative deviation of the speed of gravitational waves from the speed of light. We show that the existing constraints from pulsar timing measurements already place stringent limits on $\epsilon$ and consequently on the mass of graviton $m_g$. These limits on $m_g$ are three orders of magnitude stronger than the current constraints from Solar System tests. The current constraints also allow to rule out massive gravitons as possible candidates for cold dark matter in galactic halo. In the near future, the gravitational wave background from extragalactic super massive black hole binaries, along with the expected sub-microsecond pulsar timing accuracy, will allow to achieve constrains of $\epsilon\lesssim 0.4\%$ and possibly stronger.

0805.3103
(/preprints)

2008-05-22, 08:35
**[edit]**

**Authors**: Pedro J. Montero, Jose A. Font, Masaru Shibata

**Date**: 20 May 2008

**Abstract**: We present a new two-dimensional numerical code called Nada designed to solve the full Einstein equations coupled to the general relativistic hydrodynamics equations. The code is mainly intended for studies of self-gravitating accretion disks (or tori) around black holes, although it is also suitable for regular spacetimes. Concerning technical aspects the Einstein equations are formulated and solved in the code using a formulation of the standard 3+1 (ADM) system, the so-called BSSN approach. A key feature of the code is that derivative terms in the spacetime evolution equations are computed using a fourth-order centered finite difference approximation in conjunction with the Cartoon method to impose the axisymmetry condition under Cartesian coordinates (the choice in Nada), and the puncture/moving puncture approach to carry out black hole evolutions. Correspondingly, the general relativistic hydrodynamics equations are written in flux-conservative form and solved with high-resolution, shock-capturing schemes. We perform and discuss a number of tests to assess the accuracy and expected convergence of the code, namely (single) black hole evolutions, shock tubes, and evolutions of both spherical and rotating relativistic stars in equilibrium, the gravitational collapse of a spherical relativistic star leading to the formation of a black hole. In addition, paving the way for specific applications of the code, we also present results from fully general relativistic numerical simulations of a system formed by a black hole surrounded by a self-gravitating torus in equilibrium.

0805.3099
(/preprints)

2008-05-21, 08:36
**[edit]**

**Authors**: Jan Steinhoff, Gerhard Schäfer, Steven Hergt

**Date**: 20 May 2008

**Abstract**: In general relativity, systems of spinning classical particles are implemented into the canonical formalism of Arnowitt, Deser, and Misner [1]. The implementation is made with the aid of a symmetric stress-energy tensor and not a 4-dimensional covariant action functional. The formalism is valid to terms linear in the single spin variables and up to and including the next-to-leading order approximation in the gravitational spin-interaction part. The field-source terms for the spinning particles occurring in the Hamiltonian are obtained from their expressions in Minkowski space with canonical variables through 3-dimensional covariant generalizations as well as from a suitable shift of projections of the curved spacetime stress-energy tensor originally given within covariant spin supplementary conditions. The applied coordinate conditions are the generalized isotropic ones introduced by Arnowitt, Deser, and Misner. As applications, the Hamiltonian of two spinning compact bodies with next-to-leading order gravitational spin-orbit coupling, recently obtained by Damour, Jaranowski, and Sch\"afer [2], is rederived and the derivation of the next-to-leading order gravitational spin(1)-spin(2) Hamiltonian, shown for the first time in [3], is presented.

0805.3136
(/preprints)

2008-05-21, 08:36
**[edit]**

**Authors**: Pablo Cerdá-Durán, José A. Font, Luis Antón, Ewald Müller

**Date**: 29 Apr 2008

**Abstract**: We present a new numerical code which solves the general relativistic magneto-hydrodynamics (GRMHD) equations coupled to the Einstein equations for the evolution of a dynamical spacetime. This code has been developed with the main objective of studying astrophysical scenarios in which both, high magnetic fields and strong gravitational fields appear, such as the magneto-rotational collapse of stellar cores, the collapsar model of GRBs, and the evolution of neutron stars. The code is based on an existing and thoroughly tested purely hydrodynamics code and on its extension to accommodate weakly magnetized fluids (passive magnetic field approximation). The numerical code we present here is based on high-resolution shock-capturing schemes to solve the GRMHD equations together with the flux constraint transport method to ensure the solenoidal condition of the magnetic field. Since the astrophysical applications envisaged do not deviate much from spherical symmetry, the conformal flatness condition approximation is used for the formulation of the Einstein equations. In addition, the code can handle several equations of state, from simple analytical expressions to microphysical tabulated ones. In this paper we present stringent tests of our new GRMHD numerical code, which show its ability to handle all aspects appearing in the astrophysical scenarios for which the code is intended, namely relativistic shocks, highly magnetized fluids, and equilibrium configurations of magnetized neutron stars. As an application, magneto-rotational core collapse simulations of a realistic progenitor are presented, comparing the results with our previous finding in the passive magnetic field approximation.

0804.4572
(/preprints)

2008-05-20, 09:03
**[edit]**

**Authors**: R. Gouaty, for the LIGO Scientific Collaboration

**Date**: 15 May 2008

**Abstract**: The LIGO Scientific Collaboration (LSC) is developing and running analysis pipelines to search for gravitational-wave transients emitted by astrophysical events such as compact binary mergers or core-collapsed supernovae. However, because of the non-Gaussian, non-stationary nature of the noise exhibited by the LIGO detectors, residual false alarms might be found at the end of the pipelines. A critical aspect of the search is then to assess our confidence for gravitational waves and to distinguish them from those false alarms. Both the ''Compact Binary Coalescence'' and the ''Burst'' working groups have been developing a detection checklist for the validation of candidate-events, consisting of a series of tests including data quality checks, analysis of the candidate appearance, parameter consistency studies, coherent analysis, which aim to corroborate a detection or to eliminate a false alarm. In this paper, the general methodology used for candidate validation is presented. The method is illustrated with an example of simulated gravitational wave signal and a false alarm.

0805.2412
(/preprints)

2008-05-20, 09:00
**[edit]**

**Authors**: Jonathan R. McDonald, Warner A. Miller

**Date**: 15 May 2008

**Abstract**: The Riemann scalar curvature plays a central role in Einstein's geometric theory of gravity. We describe a new geometric construction of this scalar curvature invariant at an event (vertex) in a discrete spacetime geometry. This allows one to constructively measure the scalar curvature using only clocks and photons. Given recent interest in discrete pre-geometric models of quantum gravity, we believe is it ever so important to reconstruct the curvature scalar with respect to a finite number of communicating observers. This derivation makes use of a new fundamental lattice cell built from elements inherited from both the original simplicial (Delaunay) spacetime and its circumcentric dual (Voronoi) lattice. The orthogonality properties between these two lattices yield an expression for the vertex-based scalar curvature which is strikingly similar to the corresponding hinge-based expression in Regge calculus (deficit angle per unit Voronoi dual area). In particular, we show that the scalar curvature is simply a vertex-based weighted average of deficits per weighted average of dual areas.

0805.2411
(/preprints)

2008-05-20, 09:00
**[edit]**

**Authors**: Abdul H. Mroué, Lawrence E. Kidder, Saul A. Teukolsky

**Date**: 15 May 2008

**Abstract**: We test the resummation techniques used in developing Padé and Effective One Body (EOB) waveforms for gravitational wave detection. Convergence tests show that Padé approximants of the gravitational wave energy flux do not accelerate the convergence of the standard Taylor approximants even in the test mass limit, and there is no reason why Padé transformations should help in estimating parameters better in data analysis. Moreover, adding a pole to the flux seems unnecessary in the construction of these Padé-approximated flux formulas. Padé approximants may be useful in suggesting the form of fitting formulas. We compare a 15-orbit numerical waveform of the Caltech-Cornell group to the suggested Padé waveforms of Damour et al. in the equal mass, nonspinning quasi-circular case. The comparison suggests that the Padé waveforms do not agree better with the numerical waveform than the standard Taylor based waveforms. Based on this result, we design a simple EOB model by modifiying the ET EOB model of Buonanno et al., using the Taylor series of the flux with an unknown parameter at the fourth post-Newtonian order that we fit for. This simple EOB model generates a waveform having a phase difference of only 0.002 radians with the numerical waveform, much smaller than 0.04 radians the phase uncertainty in the numerical data itself. An EOB Hamiltonian can make use of a Padé transformation in its construction, but this is the only place Padé transformations seem useful.

0805.2390
(/preprints)

2008-05-16, 09:39
**[edit]**

**Authors**: K Yamamoto, T Uchiyama, S Miyoki, M Ohashi, K Kuroda, H Ishitsuka, T Akutsu, S Telada, T Tomaru, T Suzuki, N Sato, Y Saito, Y Higashi, T Haruyama, A Yamamoto, T Shintomi, D Tatsumi, M Ando, H Tagoshi, N Kanda, N Awaya, S Yamagishi, H Takahashi, A Araya, A Takamori, S Takemoto, T Higashi, H Hayakawa, W Morii, J Akamatsu

**Date**: 15 May 2008

**Abstract**: CLIO (Cryogenic Laser Interferometer Observatory) is a Japanese gravitational wave detector project. One of the main purposes of CLIO is to demonstrate thermal-noise suppression by cooling mirrors for a future Japanese project, LCGT (Large-scale Cryogenic Gravitational Telescope). The CLIO site is in Kamioka mine, as is LCGT. The progress of CLIO between 2005 and 2007 (room- and cryogenic-temperature experiments) is introduced in this article. In a room-temperature experiment, we made efforts to improve the sensitivity. The current best sensitivity at 300 K is about $6 \times 10ˆ{-21} /\sqrt{\rm Hz}$ around 400 Hz. Below 20 Hz, the strain (not displacement) sensitivity is comparable to that of LIGO, although the baselines of CLIO are 40-times shorter (CLIO: 100m, LIGO: 4km). This is because seismic noise is extremely small in Kamioka mine. We operated the interferometer at room temperature for gravitational wave observations. We obtained 86 hours of data. In the cryogenic experiment, it was confirmed that the mirrors were sufficiently cooled (14 K). However, we found that the radiation shield ducts transferred 300K radiation into the cryostat more effectively than we had expected. We observed that noise caused by pure aluminum wires to suspend a mirror was suppressed by cooling the mirror.

0805.2384
(/preprints)

2008-05-16, 09:39
**[edit]**

**Authors**: Ilya Mandel, Duncan A. Brown, Jonathan R. Gair, M. Coleman Miller

**Date**: 2 May 2007

**Abstract**: Gravitational waves (GWs) from the inspiral of a neutron star (NS) or stellar-mass black hole (BH) into an intermediate-mass black hole (IMBH) with mass between ~50 and ~350 solar masses may be detectable by the planned advanced generation of ground-based GW interferometers. Such intermediate mass ratio inspirals (IMRIs) are most likely to be found in globular clusters. We analyze four possible IMRI formation mechanisms: (1) hardening of an NS-IMBH or BH-IMBH binary via three-body interactions, (2) hardening via Kozai resonance in a hierarchical triple system, (3) direct capture, and (4) inspiral of a compact object from a tidally captured main-sequence star; we also discuss tidal effects when the inspiraling object is an NS. For each mechanism we predict the typical eccentricities of the resulting IMRIs. We find that IMRIs will have largely circularized by the time they enter the sensitivity band of ground-based detectors. Hardening of a binary via three-body interactions, which is likely to be the dominant mechanism for IMRI formation, yields eccentricities under 10ˆ-4 when the GW frequency reaches 10 Hz. Even among IMRIs formed via direct captures, which can have the highest eccentricities, around 90% will circularize to eccentricities under 0.1 before the GW frequency reaches 10 Hz. We estimate the rate of IMRI coalescences in globular clusters and the sensitivity of a network of three Advanced LIGO detectors to the resulting GWs. We show that this detector network may see up to tens of IMRIs per year, although rates of one to a few per year may be more plausible. We also estimate the loss in signal-to-noise ratio that will result from using circular IMRI templates for data analysis and find that, for the eccentricities we expect, this loss is negligible.

0705.0285
(/preprints)

2008-05-14, 18:10
**[edit]**

**Authors**: Latham Boyle, Michael Kesden (CITA)

**Date**: 18 Dec 2007

**Abstract**: In a recent paper arXiv:0709.0299, we introduced a spin expansion that provides a simple yet powerful way to understand aspects of binary black hole (BBH) merger. This approach relies on the symmetry properties of initial and final quantities like the black hole mass m, kick velocity {\bf k}, and spin vector {\bf s}, rather than a detailed understanding of the merger dynamics. In this paper, we expand on this proposal, examine how well its predictions agree with current simulations, and discuss several future directions that would make it an even more valuable tool. The spin expansion yields many new predictions, including several exact results that may be useful for testing numerical codes. Some of these predictions have already been confirmed, while others await future simulations. We explain how a relatively small number of simulations -- 10 equal-mass simulations, and 16 unequal-mass simulations -- may be used to calibrate all of the coefficients in the spin expansion up to second order at the minimum computational cost. For a more general set of simulations of given covariance, we derive the minimum-variance unbiased estimators for the spin expansion coefficients. We discuss how this calibration would be interesting and fruitful for general relativity and astrophysics. Finally, we sketch the extension to eccentric orbits.

0712.2819
(/preprints)

2008-05-14, 18:10
**[edit]**

**Authors**: John T. Whelan, Reinhard Prix, Deepak Khurana

**Date**: 14 May 2008

**Abstract**: We report on our F-statistic search for white-dwarf binary signals in the Mock LISA Data Challenge 1B (MLDC1B). We focus in particular on the improvements in our search pipeline since MLDC1, namely refinements in the search pipeline and the use of a more accurate detector response (rigid adiabatic approximation). The search method employs a hierarchical template-grid based exploration of the parameter space, using a coincidence step to distinguish between primary (‘true’) and secondary maxima, followed by a final (multi-TDI) ‘zoom’ stage to provide an accurate parameter estimation of the final candidates.

0805.1972
(/preprints)

2008-05-14, 18:07
**[edit]**

**Authors**: Marc van der Sluys, Vivien Raymond, Ilya Mandel, Christian Roever, Nelson Christensen, Vicky Kalogera, Renate Meyer, Alberto Vecchio

**Date**: 12 May 2008

**Abstract**: We present a Markov-chain Monte-Carlo (MCMC) technique to study the source parameters of gravitational-wave signals from the inspirals of stellar-mass compact binaries detected with ground-based gravitational-wave detectors such as LIGO and Virgo, for the case where spin is present in the more massive compact object in the binary. We discuss aspects of the MCMC algorithm that allow us to sample the parameter space in an efficient way. We show sample runs that illustrate the possibilities of our MCMC code and the difficulties that we encounter.

0805.1689
(/preprints)

2008-05-12, 23:05
**[edit]**

**Authors**: John G. Baker, William D. Boggs, Joan Centrella, Bernard J. Kelly, Sean T. McWilliams, James R. van Meter

**Date**: 9 May 2008

**Abstract**: We present a detailed descriptive analysis of the gravitational radiation from black-hole binary mergers of non-spinning black holes, based on numerical simulations of systems varying from equal-mass to a 6:1 mass ratio. Our primary goal is to present relatively complete information about the waveforms, including all the leading multipolar components, to interested researchers. In our analysis, we pursue the simplest physical description of the dominant features in the radiation, providing an interpretation of the waveforms in terms of an {\em implicit rotating source}. This interpretation applies uniformly to the full wavetrain, from inspiral through ringdown. We emphasize strong relationships among the $\ell=m$ modes that persist through the full wavetrain. Exploring the structure of the waveforms in more detail, we conduct detailed analytic fitting of the late-time frequency evolution, identifying a key quantitative feature shared by the $\ell=m$ modes among all mass-ratios. We identify relationships, with a simple interpretation in terms of the implicit rotating source, among the evolution of frequency and amplitude, which hold for the late-time radiation. These detailed relationships provide sufficient information about the late-time radiation to yield a predictive model for the late-time waveforms, an alternative to the common practice of modeling by a sum of quasinormal mode overtones. We demonstrate an application of this in a new effective-one-body-based analytic waveform model.

0805.1428
(/preprints)

2008-05-12, 23:05
**[edit]**

**Authors**: M. I. Krivoruchenko

**Date**: 8 May 2008

**Abstract**: Using elementary geometric tools, we derive essentially in the same way expressions for rotation angle of the swing plane of Foucault's pendulum and rotation angle of spin of relativistic particle moving along circular orbit (Thomas precession effect).

0805.1136
(/preprints)

2008-05-12, 08:40
**[edit]**

**Authors**: Francesco Sylos Labini, Nikolay L. Vasilyev, Luciano Pietronero, Yurij V. Baryshev

**Date**: 8 May 2008

**Abstract**: The determination of the properties of the galaxy distribution at large scales is accomplished using statistics which are assumed to be self-averaging inside a given sample. We present a new analysis able to quantitatively map galaxy large scale structures while testing for the stability of average statistical quantities in different sample regions. We find that the newest samples of the Sloan Digital Sky Survey provide unambiguous evidence that galaxy structures correspond to large amplitude density fluctuations at all scales limited only by sample sizes. The two-point correlations properties are self-averaging up to approximately 30 Mpc/h and are characterized by a fractal dimension D=2.1\pm 0.1. Then at all larger scales probed density fluctuations are too large in amplitude and too extended in space to be self-averaging inside the considered volumes. These inhomogeneities are compatible with a continuation of fractal correlations but incompatible with a homogeneity scale smaller than 100 Mpc/h and with the predictions of standard theoretical models and of gravitationally modeled mock galaxy catalogs.

0805.1132
(/preprints)

2008-05-12, 08:40
**[edit]**

**Authors**: Sam R. Dolan

**Date**: 8 May 2008

**Abstract**: The scattering cross section for a long-wavelength planar gravitational wave impinging upon a rotating black hole is calculated, for the special case in which the direction of incidence is aligned with the rotation axis. We show that black hole rotation leads to a term in the cross section that is proportional to $a\omega$. Hence, contrary to some claims, co-rotating and counter-rotating helicities are scattered differently, and a partial polarization is induced in an unpolarized incident wave.

The scattering amplitudes are found via partial wave series. To compute the series, two ingredients are required: phase shifts and spin-weighted spheroidal harmonics. We show that the phase shifts may be found from low-frequency solutions of the radial Teukolsky equation derived by Mano, Suzuki and Takasugi. The spheroidal harmonics may be expanded in spherical harmonics; we present expansions accurate to second order in $a \omega$. The two ingredients are combined to give explicit expressions for the helicity-conserving and helicity-reversing amplitudes, valid in the long-wavelength limit.

0805.1236
(/preprints)

2008-05-12, 08:39
**[edit]**

**Authors**: L. Gualtieri, E. Berti, V. Cardoso, U. Sperhake

**Date**: 7 May 2008

**Abstract**: We study the transformation of multipolar decompositions of gravitational radiation under rotations and boosts. Rotations to the remnant black hole's frame simplify the waveforms from the merger of generic spinning black hole binaries. Boosts may be important to get an accurate gravitational-wave phasing, especially for configurations leading to large recoil velocities of the remnant. As a test of our formalism we revisit the classic problem of point particles falling into a Schwarzschild black hole. Then we highlight by specific examples the importance of choosing the right frame in numerical simulations of unequal-mass, spinning binary black-hole mergers.

0805.1017
(/preprints)

2008-05-08, 18:55
**[edit]**

**Authors**: S. Desai (Penn State), E.O. Kahya (Florida), R.P. Woodard (Florida)

**Date**: 23 Apr 2008

**Abstract**: We discuss the implications for gravity wave detectors of a class of modified gravity theories which dispense with the need for dark matter. These models, which are known as Dark Matter Emulators, have the property that weak gravitational waves couple to the metric that would follow from general relativity without dark matter whereas ordinary particles couple to a combination of the metric and other fields which reproduces the result of general relativity with dark matter. We show that there is an appreciable difference in the Shapiro delays of gravitational waves and photons or neutrinos from the same source, with the gravity waves always arriving first. We compute the expected time lags for GRB 070201, for SN 1987a, and for Sco-X1. We estimate the probable error by taking account of the uncertainty in position, and by using three different dark matter profiles.

0804.3804
(/preprints)

2008-05-06, 09:35
**[edit]**

**Authors**: Carlos O. Lousto, Yosef Zlochower

**Date**: 1 May 2008

**Abstract**: We measure the gravitational recoil for unequal-mass-black-hole-binary mergers, with the larger BH having spin a/m=0.8, and the smaller BH non-spinning. We choose our configurations such that, initially, the spins lie on the orbital plane. The spin and orbital plane precess significantly, and we find that the out-of plane recoil (i.e. the recoil perpendicular to the orbital plane around merger) varies as etaˆ2/(1+q), in agreement with our previous prediction, based on the post-Newtonian scaling.

0805.0159
(/preprints)

2008-05-05, 09:05
**[edit]**

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

*Tantum in modicis, quantum in maximis*