[0909.4263] Modeling Extreme Mass Ratio Inspirals within the Effective-One-Body Approach

Authors: Nicolas Yunes, Alessandra Buonanno, Scott A. Hughes, M. Coleman Miller, Yi Pan

Date: 23 Sep 2009

Abstract: We present the first models of extreme-mass-ratio inspirals within the effective-one-body (EOB) formalism, focusing on quasi-circular orbits into non-rotating black holes. We show that the phase difference and (Newtonian normalized) amplitude difference between EOB and Teukolsky-based gravitational waveforms can be reduced to < 0.1 rads and < 0.002, respectively, after a 2-year evolution. The inclusion of post-Newtonian self-force terms in the EOB approach leads to a phase disagreement of ~6-27 rads after a 2-year evolution. Such inclusion could also allow for the EOB modeling of waveforms from intermediate-mass ratio, quasi-circular inspirals.

abs pdf

Sep 24, 2009

0909.4263 (/preprints)
2009-09-24, 08:47 [edit]


[0909.4150] Generalized Kerr spacetime with an arbitrary mass quadrupole moment: geometric properties vs particle motion

Authors: Donato Bini, Andrea Geralico, Orlando Luongo, Hernando Quevedo

Date: 23 Sep 2009

Abstract: An exact solution of Einstein's field equations in empty space first found in 1985 by Quevedo and Mashhoon is analyzed in detail. This solution generalizes Kerr spacetime to include the case of matter with arbitrary mass quadrupole moment and is specified by three parameters, the mass $M$, the angular momentum per unit mass $a$ and the quadrupole parameter $q$. It reduces to the Kerr spacetime in the limiting case $q=0$ and to the Erez-Rosen spacetime when the specific angular momentum $a$ vanishes. The geometrical properties of such a solution are investigated. Causality violations, directional singularities and repulsive effects occur in the region close to the source. Geodesic motion and accelerated motion are studied on the equatorial plane which, due to the reflection symmetry property of the solution, turns out to be also a geodesic plane.

abs pdf

Sep 24, 2009

0909.4150 (/preprints)
2009-09-24, 08:47 [edit]


[0909.3756] Multipolar equations of motion for extended test bodies in General Relativity

Authors: Jan Steinhoff, Dirk Puetzfeld

Date: 21 Sep 2009

Abstract: We derive the equations of motion of an extended test body in the context of Einstein's theory of gravitation. The equations of motion are obtained via a multipolar approximation method and are given up to the quadrupolar order. Special emphasis is put on the explicit construction of the so-called canonical form of the energy-momentum density. The set of gravitational multipolar moments and the corresponding equations of motion allow for a systematic comparison to competing multipolar approximation schemes.

abs pdf

Sep 24, 2009

0909.3756 (/preprints)
2009-09-24, 08:47 [edit]


[0909.3636] Testing Effective Quantum Gravity with Gravitational Waves from Extreme-Mass-Ratio Inspirals

Authors: Nicolas Yunes, C. F. Sopuerta

Date: 20 Sep 2009

Abstract: Testing deviation of GR is one of the main goals of the proposed {\emph{Laser Interferometer Space Antenna}}, a space-based gravitational-wave observatory. For the first time, we consistently compute the generation of gravitational waves from extreme-mass ratio inspirals (stellar compact objects into supermassive black holes) in a well-motivated alternative theory of gravity, that to date remains weakly constrained by double binary pulsar observations. The theory we concentrate on is Chern-Simons (CS) modified gravity, a 4-D, effective theory that is motivated both from string theory and loop-quantum gravity, and which enhances the Einstein-Hilbert action through the addition of a dynamical scalar field and the parity-violating Pontryagin density. We show that although point particles continue to follow geodesics in the modified theory, the background about which they inspiral is a modification to the Kerr metric, which imprints a CS correction on the gravitational waves emitted. CS modified gravitational waves are sufficiently different from the General Relativistic expectation that they lead to significant dephasing after 3 weeks of evolution, but such dephasing will probably not prevent detection of these signals, but instead lead to a systematic error in the determination of parameters. We end with a study of radiation-reaction in the modified theory and show that, to leading-order, energy-momentum emission is not CS modified, except possibly for the subdominant effect of scalar-field emission. The inclusion of radiation-reaction will allow for tests of CS modified gravity with space-borne detectors that might be two orders of magnitude larger than current binary pulsar bounds.

abs pdf

Sep 24, 2009

0909.3636 (/preprints)
2009-09-24, 08:47 [edit]


[0909.3557] Simulations of Binary Black Hole Mergers Using Spectral Methods

Authors: B&#xe9;la Szil&#xe1;gyi, Lee Lindblom, Mark A. Scheel

Date: 21 Sep 2009

Abstract: Several improvements in numerical methods and gauge choice are presented that make it possible now to perform simulations of the merger and ringdown phases of "generic" binary black-hole evolutions using the pseudo-spectral evolution code SpEC. These improvements include the use of a new damped-wave gauge condition, a new grid structure with appropriate filtering that improves stability, and better adaptivity in conforming the grid structures to the shapes and sizes of the black holes. Simulations illustrating the success of these new methods are presented for a variety of binary black-hole systems. These include fairly ‘generic’ systems with unequal masses (up to 2:1 mass ratios), and spins (with magnitudes up to 0.4 Mˆ2) pointing in various directions.

abs pdf

Sep 24, 2009

0909.3557 (/preprints)
2009-09-24, 08:47 [edit]


[0909.4039] An exploration of CUDA and CBEA for a gravitational wave source-modelling application

Authors: Gaurav Khanna, Justin McKennon

Date: 22 Sep 2009

Abstract: In this paper, we accelerate a gravitational physics numerical modelling application using hardware accelerators -- Cell processor and Tesla CUDA GPU. We describe these new technologies and our approach in detail, and then present our final performance results. We obtain well over an order-of-magnitude performance gain in our application by making use of these many-core architectures.

abs pdf

Sep 23, 2009

0909.4039 (/preprints)
2009-09-23, 08:38 [edit]


[0909.3474] Relativistic Fluids and the Physics of Gravitational Collapse

Authors: L. Herrera

Date: 18 Sep 2009

Abstract: We present a discussion on some physical aspects of gravitational collapse which is based on a list of questions related to relevant issues in the study of that phenomenon. Providing answers to those questions we bring out the role played by different physical processes in the dynamics of spherical collapse.

abs pdf

Sep 21, 2009

0909.3474 (/preprints)
2009-09-21, 10:47 [edit]


[0907.3318] Parameter estimation for coalescing massive binary black holes with LISA using the full 2-post-Newtonian gravitational waveform and spin-orbit precession

Authors: Antoine Klein, Philippe Jetzer, Mauro Sereno

Date: 20 Jul 2009

Abstract: With one exception, previous analyses of the measurement accuracy of gravitational wave experiments for comparable-mass binary systems have neglected either spin-precession effects or subdominant harmonics and amplitude modulations. Here we give the first explicit description of how these effects combine to improve parameter estimation. We consider supermassive black hole binaries as expected to be observed with the planned space-based interferometer LISA, and study the measurement accuracy for several astrophysically interesting parameters obtainable taking into account the full 2PN waveform for spinning bodies, as well as spin-precession effects. We find that for binaries with a total mass in the range 10ˆ5 M_Sun < M < 10ˆ7 M_Sun at a redshift of 1, a factor ~1.5 is in general gained in accuracy, with the notable exception of the determination of the individual masses in equal-mass systems, for which a factor ~5 can be gained. We also find, as could be expected, that using the full waveform helps increasing the upper mass limit for detection, which can be as high as M = 10ˆ8 M_Sun at a redshift of 1, as well as the redshift limit where some information can be extracted from a system, which is roughly z = 10 for M < 10ˆ7 M_Sun, 1.5-5 times higher than with the restricted waveform. We computed that the full waveform allows to use supermassive black hole binaries as standard sirens up to a redshift of z = 1.6, about 0.4 larger than what previous studies allowed. We found that for lower unequal-mass binary systems, the measurement accuracy is not as drastically improved as for other systems. This suggests that for these systems, adding parameters such as eccentricity or alternative gravity parameters could be achieved without much loss in the accuracy.

abs pdf

Sep 21, 2009

0907.3318 (/preprints)
2009-09-21, 10:47 [edit]


[0909.3456] Antigravitation

Authors: Sabine Hossenfelder

Date: 18 Sep 2009

Abstract: We discuss why there are no negative gravitational sources in General Relativity and show that it is possible to extend the classical theory such that repulsive gravitational interaction occurs.

abs pdf

Sep 21, 2009

0909.3456 (/preprints)
2009-09-21, 10:46 [edit]


[0909.3328] Fundamental Theoretical Bias in Gravitational Wave Astrophysics and the Parameterized Post-Einsteinian Framework

Authors: Nicolas Yunes, Frans Pretorius

Date: 17 Sep 2009

Abstract: We consider the concept of fundamental bias in gravitational wave astrophysics as the assumption that general relativity is the correct theory of gravity during the entire wave-generation and propagation regime. Such an assumption is valid in the weak-field, as verified by precision experiments and observations, but it need not hold in the dynamical strong-field regime where tests are lacking. Fundamental bias can cause systematic errors in the detection and parameter estimation of signals, which can lead to a mischaracterization of the universe through incorrect inferences about source event rates and populations. We propose a remedy through the introduction of the parameterized post-Einsteinian framework, which consists of the enhancement of waveform templates via the inclusion of post-Einsteinian parameters. These parameters would ostensibly be designed to interpolate between templates constructed in general relativity and well-motivated alternative theories of gravity, and also include extrapolations that follow sound theoretical principles, such as consistency with conservation laws and symmetries. As an example, we construct parameterized post-Einsteinian templates for the binary coalescence of equal-mass, non-spinning compact objects in a quasi-circular inspiral. The parametrized post-Einsteinian framework should allow matched filtered data to select a specific set of post-Einsteinian parameters without a priori assuming the validity of the former, thus either verifying general relativity or pointing to possible dynamical strong-field deviations.

abs pdf

Sep 21, 2009

0909.3328 (/preprints)
2009-09-21, 10:45 [edit]


[0909.2867] "Complete" gravitational waveforms for black-hole binaries with non-precessing spins

Authors: P. Ajith, M. Hannam, S. Husa, Y. Chen, B. Bruegmann, N. Dorband, D. Mueller, F. Ohme, D. Pollney, C. Reisswig, L. Santamaria, J. Seiler

Date: 15 Sep 2009

Abstract: We present the first analytical inspiral-merger-ringdown gravitational waveforms from black-hole (BH) binaries with non-precessing spins. By matching a post-Newtonian description of the inspiral to a set of numerical calculations performed in full general relativity, we obtain a waveform family with a conveniently small number of physical parameters. The physical content of these waveforms includes the "orbital hang-up" effect, when BHs are spinning rapidly along the direction of the orbital angular momentum. These waveforms will allow us to detect a larger parameter space of BH binary coalescence, to explore various scientific questions related to GW astronomy, and could dramatically improve the expected detection rates of GW detectors.

abs pdf

Sep 18, 2009

0909.2867 (/preprints)
2009-09-18, 14:48 [edit]


[0909.2994] Constructing the self-force

Authors: Eric Poisson

Date: 16 Sep 2009

Abstract: I present an overview of the methods involved in the computation of the scalar, electromagnetic, and gravitational self-forces acting on a point particle moving in a curved spacetime. For simplicity, the focus here will be on the scalar self-force. The lecture follows closely my review article on this subject published in Living Reviews in Relativity. I begin with a review of geometrical elements (Synge's world function, the parallel propagator). Next I introduce useful coordinate systems (Fermi normal coordinates and retarded light-cone coordinates) in a neighborhood of the particle's world line. I then present the wave equation for a scalar field in curved spacetime and the equations of motion for a particle endowed with a scalar charge. The wave equation is solved by means of a Green's function, and the self-force is constructed from the field gradient. Because the retarded field is singular on the world line, the self-force must involve a regularized version of the field gradient, and I describe how the regular piece of the self-field can be identified. In the penultimate section of the lecture I put the construction of the self-force on a sophisticated axiomatic basis, and in the concluding section I explain how one can do better by abandoning the dangerous fiction of a point particle

abs pdf

Sep 18, 2009

0909.2994 (/preprints)
2009-09-18, 14:48 [edit]


[0909.2411] Probing Tensor-Vector-Scalar Theory with Gravitational Wave Asteroseismology

Authors: Hajime Sotani

Date: 13 Sep 2009

Abstract: In order to examine the gravitational waves emitted from the neutron stars in the tensor-vector-scalar (TeVeS) theory, we derive the perturbation equations for relativistic stars, where for simplicity we omit the perturbations of vector field. That is, we consider the perturbations of scalar and tensor fields. With this assumption, we find that the axial gravitational waves, which are corresponding to the oscillations of spacetime ($w$ modes), are independent from the perturbations of scalar field and the effects of scalar field can be mounted only via the background properties. Using two different equations of state, we calculate the complex eigenfrequencies of axial $w$ modes and find that the dependences of frequencies on the stellar compactness are almost independent from the adopted equation of state and the parameter in TeVeS. Additionally, these dependences of frequencies of axial $w$ modes in TeVeS is obviously different from those expected in the general relativity. Thus the direct observations of gravitational waves could reveal the gravitational theory in the strong-field regime.

abs pdf

Sep 18, 2009

0909.2411 (/preprints)
2009-09-18, 14:48 [edit]


[0907.1169] Stable indications of relic gravitational waves in Wilkinson Microwave Anisotropy Probe data and forecasts for the Planck mission

Authors: W. Zhao, D. Baskaran, L. P. Grishchuk

Date: 7 Jul 2009

Abstract: The relic gravitational waves (gw) are the cleanest probe of the violent times in the very early history of the Universe. They are expected to leave signatures in the observed cosmic microwave background anisotropies. We significantly improved our previous analysis [1] of the 5-year WMAP $TT$ and $TE$ data at lower multipoles $\ell$. This more general analysis returned essentially the same maximum likelihood (ML) result (unfortunately, surrounded by large remaining uncertainties): the relic gw are present and they are responsible for approximately 20% of the temperature quadrupole. We identify and discuss the reasons by which the contribution of gw can be overlooked in a data analysis. One of the reasons is a misleading reliance on data from very high multipoles $\ell$, another - a too narrow understanding of the problem as the search for $B$-modes of polarization, rather than the detection of relic gw with the help of all correlation functions. Our analysis of WMAP5 data has led to the identification of a whole family of models characterized by relatively high values of the likelihood function. Using the Fisher matrix formalism we formulated forecasts for {\it Planck} mission in the context of this family of models. We explore in details various ‘optimistic’, ‘pessimistic’ and ‘dream case’ scenarios. We show that in some circumstances the $B$-mode detection may be very inconclusive, at the level of signal-to-noise ratio $S/N =1.75$, whereas a smarter data analysis can reveal the same gw signal at $S/N= 6.48$. The final result is encouraging. Even under unfavourable conditions in terms of instrumental noises and foregrounds, the relic gw, if they are characterized by the ML parameters that we found from WMAP5 data, will be detected by {\it Planck} at the level $S/N = 3.65$.

abs pdf

Sep 18, 2009

0907.1169 (/preprints)
2009-09-18, 14:46 [edit]


[0909.1796] The influence of short term variations in AM CVn systems on LISA measurements

Authors: Alexander Stroeer, Gijs Nelemans

Date: 9 Sep 2009

Abstract: We study the effect of short term variations of the evolution of AM CVn systems on their gravitational wave emissions and in particular LISA observations. We model the systems according to their equilibrium mass-transfer evolution as driven by gravitational wave emission and tidal interaction, and determine their reaction to a sudden perturbation of the system. This is inspired by the suggestion to explain the orbital period evolution of the ultra-compact binary systems V407 Vul and RX-J0806+1527 by non-equilibrium mass transfer. The characteristics of the emitted gravitational wave signal are deduced from a Taylor expansion of a Newtonian quadrupolar emission model, and the changes in signal structure as visible to the LISA mission are determined. We show that short term variations can significantly change the higher order terms in the expansion, and thus lead to spurious (non) detection of frequency derivatives. This may hamper the estimation of the parameters of the system, in particular their masses and distances. However, we find that overall detection is still secured as signals still can be described by general templates. We conclude that a better modelling of the effects of short term variations is needed to prepare the community for astrophysical evaluations of real gravitational wave data of AM CVn systems.

abs pdf

Sep 10, 2009

0909.1796 (/preprints)
2009-09-10, 02:44 [edit]


[0909.0742] Observing gravitational wave bursts in pulsar timing measurements

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

Date: 3 Sep 2009

Abstract: We propose a novel method for observing the gravitational wave signature of super-massive black hole (SMBH) mergers. This method is based on detection of a specific type of gravitational waves, namely gravitational wave burst with memory (BWM), using pulsar timing. We study the unique signature produced by BWM in anomalous pulsar timing residuals. We show that the present day pulsar timing precision allows one to detect BWM due to SMBH mergers from distances up to $1 \rm{Gpc}$ (for case of equal mass $10ˆ8 M_{\odot}$ SMBH). Improvements in precision of pulsar timing together with the increase in number of observed pulsars should eventually lead to detection of a BWM signal due to SMBH merger, thereby making the proposed technique complementary to the capabilities of the planned LISA mission.

abs pdf

Sep 09, 2009

0909.0742 (/preprints)
2009-09-09, 04:05 [edit]


[gr-qc/0703035] Formalism and Bases of Numerical Relativity

Authors: Eric Gourgoulhon (LUTH, CNRS / Observatoire de Paris)

Date: 6 Mar 2007

Abstract: These lecture notes provide some introduction to the 3+1 formalism of general relativity, which is the foundation of most modern numerical relativity. The text is rather self-contained, with detailed calculations and numerous examples. Contents: 1. Introduction, 2. Geometry of hypersurfaces, 3. Geometry of foliations, 4. 3+1 decomposition of Einstein equation, 5. 3+1 equations for matter and electromagnetic field, 6. Conformal decomposition, 7. Asymptotic flatness and global quantities, 8. The initial data problem, 9. Choice of foliation and spatial coordinates, 10. Evolution schemes.

abs pdf

Sep 09, 2009

0703035 (/preprints/gr-qc)
2009-09-09, 03:29 [edit]


[0909.1318] The Distribution of Stars and Stellar Remnants at the Galactic Center

Authors: David Merritt

Date: 8 Sep 2009

Abstract: Motivated by recent observations that suggest a low density of old stars around the Milky Way supermassive black hole, evolutionary models for the nuclear star cluster are considered that postulate a parsec-scale core as initial conditions. Gravitational encounters cause the core to shrink; a core of initial radius 1-1.5 pc evolves to a size of 0.5 pc after 10 Gyr, roughly the size of the observed core. The absence of a Bahcall-Wolf cusp is naturally explained. In these models, the time for a 10-Solar-mass black hole to spiral in to the Galactic center from an initial distance of 5 pc can be much greater than 10 Gyr. Assuming that the stellar black holes had the same phase-space distribution initially as the stars, their density after 5-10 Gyr is predicted to rise very steeply going into the stellar core, but to remain substantially below the densities inferred from steady-state models that include a steep density cusp in the stars. The implications of these models are discussed for the rates of gravitational wave inspiral events and of other physical processes that depend on a high density of stars or stellar mass black holes near Sagittarius A*.

abs pdf

Sep 09, 2009

0909.1318 (/preprints)
2009-09-09, 03:25 [edit]


[0907.1252] Cross section, final spin and zoom-whirl behavior in high-energy black hole collisions

Authors: U. Sperhake, V. Cardoso, F. Pretorius, E. Berti, T. Hinderer, N. Yunes

Date: 7 Jul 2009

Abstract: We study the collision of two highly boosted equal mass, nonrotating black holes with generic impact parameter. We find such systems to exhibit zoom-whirl behavior when fine tuning the impact parameter. Near the threshold of immediate merger the remnant black hole Kerr parameter can be near maximal (a/M about 0.95) and the radiated energy can be as large as 35% of the center-of-mass energy.

abs pdf

Sep 09, 2009

0907.1252 (/preprints)
2009-09-09, 03:24 [edit]


[0909.1093] Bayesian reconstruction of gravitational wave burst signals from simulations of rotating stellar core collapse and bounce

Authors: Christian R&#xf6;ver, Marie-Anne Bizouard, Nelson Christensen, Harald Dimmelmeier, Ik Siong Heng, Renate Meyer

Date: 6 Sep 2009

Abstract: Presented in this paper is a technique that we propose for extracting the physical parameters of a rotating stellar core collapse from the observation of the associated gravitational wave signal from the collapse and core bounce. Data from interferometric gravitational wave detectors can be used to provide information on the mass of the progenitor model, precollapse rotation and the nuclear equation of state. We use waveform libraries provided by the latest numerical simulations of rotating stellar core collapse models in general relativity, and from them create an orthogonal set of eigenvectors using principal component analysis. Bayesian inference techniques are then used to reconstruct the associated gravitational wave signal that is assumed to be detected by an interferometric detector. Posterior probability distribution functions are derived for the amplitudes of the principal component analysis eigenvectors, and the pulse arrival time. We show how the reconstructed signal and the principal component analysis eigenvector amplitude estimates may provide information on the physical parameters associated with the core collapse event.

abs pdf

Sep 09, 2009

0909.1093 (/preprints)
2009-09-09, 03:24 [edit]


[0909.0952] A formalism for the construction of binary neutron stars with arbitrary circulation

Authors: Thomas W. Baumgarte, Stuart L. Shapiro

Date: 4 Sep 2009

Abstract: Most numerical models of binary stars - in particular neutron stars in compact binaries - assume the companions to be either corotational or irrotational. Either one of these assumptions leads to a significant simplification in the hydrodynamic equations of stationary equilibrium. In this paper we develop a new formalism for the construction of binary stars with circulation intermediate between corotational and irrotational. Generalizing the equations for irrotational flow we cast the Euler equation, which is an algebraic equation in the case of corotational or irrotational fluid flow, as an elliptic equation for a new auxiliary quantity. We also suggest a parameterized decomposition of the fluid flow that allows for a variation of the stellar circulation.

abs pdf

Sep 09, 2009

0909.0952 (/preprints)
2009-09-09, 03:24 [edit]


[0909.1313] High accuracy simulations of black hole binaries:spins anti-aligned with the orbital angular momentum

Authors: Tony Chu, Harald P. Pfeiffer, Mark A. Scheel

Date: 7 Sep 2009

Abstract: High-accuracy binary black hole simulations are presented for black holes with spins anti-aligned with the orbital angular momentum. The particular case studied represents an equal-mass binary with spins of equal magnitude S/mˆ2=0.43757 \pm 0.00001. The system has initial orbital eccentricity ~4e-5, and is evolved through 10.6 orbits plus merger and ringdown. The remnant mass and spin are M_f=(0.961109 \pm 0.000003)M and S_f/M_fˆ2=0.54781 \pm 0.00001, respectively, where M is the mass during early inspiral. The gravitational waveforms have accumulated numerical phase errors of <~ 0.1 radians without any time or phase shifts, and <~ 0.01 radians when the waveforms are aligned with suitable time and phase shifts. The waveform is extrapolated to infinity using a procedure accurate to <~ 0.01 radians in phase, and the extrapolated waveform differs by up to 0.13 radians in phase and about one percent in amplitude from the waveform extracted at finite radius r=350M. The simulations employ different choices for the constraint damping parameters in the wave zone; this greatly reduces the effects of junk radiation, allowing the extraction of a clean gravitational wave signal even very early in the simulation.

abs pdf

Sep 09, 2009

0909.1313 (/preprints)
2009-09-09, 03:24 [edit]


[0909.1228] Kadath: a spectral solver for theoretical physics

Authors: Philippe Grandclement (LUTH)

Date: 7 Sep 2009

Abstract: Kadath is a library that implements spectral methods in a very modular manner. It is designed to solve a wide class of problems that arise in the context of theoretical physics. Several types of coordinates are implemented and additional geometries can be easily encoded. Partial differential equations of various types are discretized by means of spectral methods. The resulting system is solved using a Newton-Raphson iteration. Doing so, Kadath is able to deal with strongly non-linear situations. The algorithms are validated by applying the library to four different problems of contemporary physics, in the fields of gauge field theory and general relativity

abs pdf

Sep 09, 2009

0909.1228 (/preprints)
2009-09-09, 03:24 [edit]


[0909.0622] The stochastic gravitational wave background from turbulence and magnetic fields generated by a first-order phase transition

Authors: Chiara Caprini, Ruth Durrer, Geraldine Servant

Date: 3 Sep 2009

Abstract: We analytically derive the spectrum of gravitational waves due to magneto-hydrodynamical turbulence generated by bubble collisions in a first-order phase transition. In contrast to previous studies, we take into account the fact that turbulence and magnetic fields act as sources of gravitational waves for many Hubble times after the phase transition is completed. This modifies the gravitational wave spectrum at large scales. We also model the initial stirring phase preceding the Kolmogorov cascade, while earlier works assume that the Kolmogorov spectrum is set in instantaneously. The continuity in time of the source is relevant for a correct determination of the peak position of the gravitational wave spectrum. We discuss how the results depend on assumptions about the unequal-time correlation of the source and motivate a realistic choice for it. Our treatment gives a similar peak frequency to previous analyses but the amplitude of the signal is reduced due to the use of a more realistic power spectrum for the MHD turbulence. For a strongly first-order electroweak phase transition, the signal is observable by LISA.

abs pdf

Sep 09, 2009

0909.0622 (/preprints)
2009-09-09, 03:24 [edit]


[0909.0954] Gravitational-wave memory and pulsar timing arrays

Authors: Rutger van Haasteren, Yuri Levin

Date: 4 Sep 2009

Abstract: Pulsar timing arrays (PTAs) are designed to detect gravitational waves with periods from several months to several years, e.g. those produced by by wide supermassive black-hole binaries in the centers of distant galaxies. Here we show that PTAs are also sensitive to mergers of supermassive black holes. While these mergers occur on a timescale too short to be resolvable by a PTA, they generate a change of metric due to non-linear gravitational-wave memory which persists for the duration of the experiment and could be detected. We develop the theory of the single-source detection by PTAs, and derive the sensitivity of PTAs to the gravitational-wave memory jumps. We show that mergers of $10ˆ8M_{\odot}$ black holes are $2-\sigma$-detectable (in a direction, polarization, and time-dependent way) out to co-moving distances of $\sim 1$ billion light years. Modern prediction for black-hole merger rates imply marginal to modest chance of an individual jump detection by currently developed PTAs. The sensitivity is expected to be somewhat higher for futuristic PTA experiments with SKA.

abs pdf

Sep 09, 2009

0909.0954 (/preprints)
2009-09-09, 03:21 [edit]


[0909.0261] An Electromagnetic Signature of Galactic Black Hole Binaries That Enter Their Gravitational-Wave Induced Inspiral

Authors: Abraham Loeb (Harvard)

Date: 1 Sep 2009

Abstract: Mergers of gas-rich galaxies lead to black hole binaries that coalesce as a result of dynamical friction on the ambient gas. Once the binary tightens to <10ˆ3 Schwarzschild radii, its merger is driven by the emission of gravitational waves (GWs). We show that this transition occurs generically at orbital periods of ~1-10 years and an orbital velocity V of a few thousand km/s, with a very weak dependence on the supply rate of gas (V proportional to Mdotˆ{1/8}). Therefore, as binaries enter their GW-dominated inspiral, they inevitably induce large periodic shifts in the broad emission lines of any associated quasar(s). The probability of finding a binary in tighter configurations scales as Vˆ{-8} owing to their much shorter lifetimes. Systematic monitoring of the broad emission lines of quasars on timescales of months to decades can set a lower limit on the expected rate of GW sources for LISA.

abs pdf

Sep 07, 2009

0909.0261 (/preprints)
2009-09-07, 10:32 [edit]


[0909.0650] An overview of the Laser Interferometer Space Antenna

Authors: Daniel A. Shaddock

Date: 3 Sep 2009

Abstract: The Laser Interferometer Space Antenna will detect gravitational waves with frequencies from 0.1 mHz to 1 Hz. This article provides a brief overview of LISA's science goals followed by a tutorial of the LISA measurement concept.

abs pdf

Sep 04, 2009

0909.0650 (/preprints)
2009-09-04, 09:41 [edit]


[0909.0287] Gravitational wave signatures of the absence of an event horizon. I. Nonradial oscillations of a thin-shell gravastar

Authors: Paolo Pani, Emanuele Berti, Vitor Cardoso, Yanbei Chen, Richard Norte

Date: 1 Sep 2009

Abstract: Gravitational waves from compact objects provide information about their structure, probing deep into strong-gravity regions. Here we illustrate how the presence or absence of an event horizon can produce qualitative differences in the gravitational waves emitted by ultra-compact objects. In order to set up a straw-man ultra-compact object with no event horizon, but which is otherwise almost identical to a black hole, we consider the nonrotating thin-shell gravastar model first proposed by Mazur and Mottola, which has a Schwarzschild exterior, a de Sitter interior and an infinitely thin shell with finite surface energy and tension separating the two regions. As viewed from the external space-time, the shell can be located arbitrarily close to the Schwarzschild radius, so a gravastar might seem indistinguishable from a black hole when tests are only performed on its external metric. We study the linearized dynamics of the gravastar, and in particular the junction conditions connecting internal and external gravitational perturbations. As a first application of the formalism we compute polar and axial oscillation modes of a thin-shell gravastar. We show that the quasinormal mode spectrum is completely different from that of a black hole, even in the limit when its surface redshift becomes infinite. Polar QNMs depend on the equation of state of matter on the shell and can be used to distinguish between different gravastar models. Our calculations suggest that low-compactness gravastars could be unstable when the sound speed on the shell is superluminal.

abs pdf

Sep 02, 2009

0909.0287 (/preprints)
2009-09-02, 22:57 [edit]


[0908.0755] Binaries of massive black holes in rotating clusters: Dynamics, gravitational waves, detection and the role of eccentricity

Authors: Pau Amaro-Seoane, Christoph Eichhorn, Ed Porter, Rainer Spurzem

Date: 5 Aug 2009

Abstract: The dynamical evolution of binaries of intermediate-massive black holes (IMBHs, massive black holes with a mass ranging between $10ˆ2$ and $10ˆ4 M_{\odot}$) in stellar clusters has recently received an increasing amount of attention. This is at least partially due to the fact that if the binary is hard enough to evolve to the phase at which it will start emitting gravitational waves (GWs) efficiently, there is a good probability that it will be detectable by future space-borne detectors like LISA. We study this evolution in the presence of rotation in the cluster. The eccentricity is strongly connected to the initial IMBHs velocities, and values of $\sim 0.7$ up to 0.9 are reached for low initial velocities, while almost circular orbits result if the initial velocities are increased. A Monte Carlo study indicates that these sources will be detectable by a detector such as LISA with median signal to noise ratios of between 10 and 20 over a three year period, although some events had signal to noise ratios of 300 or greater. Furthermore, one should also be able to estimate the chirp-mass with median fractional errors of $10ˆ{-4}$, reduced mass on the order of $10ˆ{-3}$ and luminosity distance on the order of $10ˆ{-1}$. Finally, these sources will have a median angular resolution in the LISA detector of about 3 square degrees, putting events firmly in the field of view of future electromagnetic detectors such as LSST.

abs pdf

Sep 02, 2009

0908.0755 (/preprints)
2009-09-02, 22:56 [edit]


[0909.0487] Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries

Authors: L&#xe1;szl&#xf3; &#xc1;. Gergely, Peter L. Biermann, Bal&#xe1;zs Mik&#xf3;czi, Zolt&#xe1;n Keresztes

Date: 2 Sep 2009

Abstract: We analyze galactic black hole mergers and their emitted gravitational waves. Such mergers have typically unequal masses with mass ratio of the order 1/10. The emitted gravitational waves carry the inprint of spins and mass quadrupoles of the binary components. Among these contributions, we consider here the quasi-precessional evolution of the spins. A method of taking into account these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5 PN and 2PN accurate spin contributions to the accumulated orbital phase is developed.

abs pdf

Sep 02, 2009

0909.0487 (/preprints)
2009-09-02, 22:56 [edit]


[0908.4363] Elementary development of the gravitational self-force

Authors: Steven Detweiler

Date: 31 Aug 2009

Abstract: The gravitational field of a particle of small mass $\mu$ moving through curved spacetime, with metric $g_{ab}$, is naturally and easily decomposed into two parts each of which satisfies the perturbed Einstein equations through $O(\mu)$. One part is an inhomogeneous field $hˆS_{ab}$ which, near the particle, looks like the Coulomb $\mu/r$ field with tidal distortion from the local Riemann tensor. This singular field is defined in a neighborhood of the small particle and does not depend upon boundary conditions or upon the behavior of the source in either the past or the future. The other part is a homogeneous field $hˆR_{ab}$. In a perturbative analysis, the motion of the particle is then best described as being a geodesic in the metric $g_{ab}+hˆR_{ab}$. This geodesic motion includes all of the effects which might be called radiation reaction and conservative effects as well.

abs pdf

Sep 02, 2009

0908.4363 (/preprints)
2009-09-02, 11:20 [edit]


[0909.0066] The Effect of Eccentricity on Searches for Gravitational-Waves from Coalescing Compact Binaries in Ground-based Detectors

Authors: Duncan A. Brown, Peter J. Zimmerman

Date: 1 Sep 2009

Abstract: Inspiralling compact binaries are expected to circularize before their gravitational-wave signals reach the sensitive frequency band of ground-based detectors. Current searches for gravitational waves from compact binaries using the LIGO and Virgo detectors therefore use circular templates to construct matched filters. Binary formation models have been proposed which suggest that some systems detectable by the LIGO--Virgo network may have non-negligible eccentricity. We investigate the ability of the restricted 3.5 post-Newtonian order TaylorF2 template bank, used by LIGO and Virgo to search for gravitational waves from compact binaries with masses $M \le 35 M_\odot$, to detect binaries with non-zero eccentricity. We model the gravitational waves from eccentric binaries using the $x$-model post-Newtonian formalism proposed by Hinder \emph{et. al.} [I. Hinder, F. Hermann, P. Laguna, and D. Shoemaker, arXiv:0806.1037v1]. We find that small residual eccentricities ($e_0 \lesssim 0.05$ at 40 Hz) do not significantly affect the ability of current LIGO searches to detect gravitational waves from coalescing compact binaries with total mass $2 M_\odot < M < 15 M_\odot$. For eccentricities $e_0 \gtrsim 0.1$, the loss in matched filter signal-to-noise ratio due to eccentricity can be significant and so templates which include eccentric effects will be required to perform optimal searches for such systems.

abs pdf

Sep 02, 2009

0909.0066 (/preprints)
2009-09-02, 11:19 [edit]


[0908.4518] Tidal interaction of a small black hole in the field of a large Kerr black hole

Authors: Simon Comeau, Eric Poisson

Date: 31 Aug 2009

Abstract: The rates at which the mass and angular momentum of a small black hole change as a result of a tidal interaction with a much larger black hole are calculated to leading order in the small mass ratio. The small black hole is either rotating or nonrotating, and it moves on a circular orbit in the equatorial plane of the large Kerr black hole. The orbits are fully relativistic, and the rates are computed to all orders in the orbital velocity V < V_{isco}, which is limited only by the size of the innermost stable circular orbit. We show that as V \to V_{isco}, the rates take on a limiting value that depends only on V_{isco} and not on the spin parameter of the large black hole.

abs pdf

Sep 02, 2009

0908.4518 (/preprints)
2009-09-02, 11:19 [edit]


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