[0902.3660] Nonlinear gravitational-wave memory from binary black hole mergers

Authors: Marc Favata (KITP)

Date: 23 Feb 2009

Abstract: Some astrophysical sources of gravitational-waves can produce a "memory effect," which causes a permanent displacement of the test masses in a freely-falling gravitational-wave detector. The Christodoulou memory is a particularly interesting nonlinear form of memory that arises from the gravitational-wave stress-energy tensor's contribution to the distant gravitational-wave field. This nonlinear memory contributes a non-oscillatory component to the gravitational-wave signal at leading (Newtonian-quadrupole) order in the waveform amplitude. Previous computations of the memory and its detectability considered only the inspiral phase of binary black hole coalescence. Using an "effective-one-body" (EOB) approach calibrated to numerical relativity simulations, as well as a simple fully-analytic model, the Christodoulou memory is computed for the inspiral, merger, and ringdown. The memory will be very difficult to detect with ground-based interferometers, but is likely to be observable in supermassive black hole mergers with LISA out to a redshift of two. Detection of the nonlinear memory could serve as an experimental test of the ability of gravity to "gravitate."

Feb 27, 2009

0902.3660 (/preprints)
2009-02-27, 09:40 

[0902.4689] Can the Known Millisecond Pulsars Help in the Detection of Intermediate-Mass Black Holes at the Centers of Globular Clusters?

Authors: T.I. Larchenkova (1), A.A. Lutovinov (2) ((1) - Astro Space Center of the P.N.Lebedev Physical Institute, Moscow, Russia, (2) - Space Research Institute, Moscow, Russia)

Date: 26 Feb 2009

Abstract: We consider the possibility of detecting intermediate-mass ($10ˆ3-10ˆ4 M_{\odot}$) black holes, whose existence at the centers of globular clusters is expected from optical and infrared observations, using precise pulse arrival timing for the millisecond pulsars in globular clusters known to date. For some of these pulsars closest to the cluster centers, we have calculated the expected delay times of pulses as they pass in the gravitational field of the central black hole. The detection of such a time delay by currently available instruments for the known pulsars is shown to be impossible at a black hole mass of $10ˆ3 M_{\odot}$ and very problematic at a black hole mass of $10ˆ4 M_{\odot}$. In addition, the signal delay will have a negligible effect on the pulsar periods and their first derivatives compared to the current accuracy of their measurements.

Feb 27, 2009

0902.4689 (/preprints)
2009-02-27, 09:40 

[0902.4077] Momentum Flow in Black Hole Binaries: I. Post-Newtonian Analysis of the Inspiral and Spin-Induced Bobbing

Authors: Drew Keppel, David A. Nichols, Yanbei Chen, Kip S. Thorne

Date: 24 Feb 2009

Abstract: A brief overview is presented of a new Caltech/Cornell research program that is exploring the nonlinear dynamics of curved spacetime in binary black hole collisions and mergers, and of an initial project in this program aimed at elucidating the flow of linear momentum in black-hole binaries (BBHs). The "gauge-dependence" (arbitrariness) in the localization of linear momentum in BBHs is discussed, along with the hope that the qualitative behavior of linear momentum will be gauge-independent. Harmonic coordinates are suggested as a possibly preferred foundation for fixing the gauge associated with linear momentum. For a BBH or other compact binary, the Landau-Lifshitz formalism is used to define the momenta of the binary's individual bodies in terms of integrals over the bodies' surfaces or interiors, and define the momentum of the gravitational field (spacetime curvature) outside the bodies as a volume integral over the field's momentum density. These definitions will be used in subsequent papers that explore the internal nonlinear dynamics of BBHs via numerical relativity. This formalism is then used, in the 1.5PN approximation, to explore momentum flow between a binary's bodies and its gravitational field during the binary's orbital inspiral. Special attention is paid to momentum flow and conservation associated with synchronous spin-induced bobbing of the black holes, in the so-called "extreme-kick configuration" (where two identical black holes have their spins lying in their orbital plane and antialigned).

Feb 27, 2009

0902.4077 (/preprints)
2009-02-27, 09:39 

[0902.4133] An algorithm for detection of extreme mass ratio inspirals in LISA data

Authors: Stanislav Babak, Jonathan R. Gair, Edward K. Porter

Date: 24 Feb 2009

Abstract: The gravitational wave signal from a compact object spiralling toward a massive black hole (MBH) is thought to be one of the most difficult sources to detect in the LISA data stream. Due to the large parameter space of possible signals and many orbital cycles spent in the sensitivity band of LISA, it has been estimated previously that of the order of 10ˆ{35} templates would be required for a fully coherent search with a template grid, which is computationally impossible. Here we describe an algorithm based on a constrained Metropolis-Hastings stochastic search which allows us to find and accurately estimate parameters of isolated EMRI signals buried in Gaussian instrumental noise. We illustrate the effectiveness of the algorithm with results from searches of the Mock LISA Data Challenge round 1B data sets.

Feb 27, 2009

0902.4133 (/preprints)
2009-02-27, 09:39 

[0902.3004] Opportunities for Probing Fundamental Gravity with Solar System Experiments

Authors: Slava G. Turyshev (Jet Propulsion Laboratory), Thomas W. Murphy, Jr. (University of California, San Diego), Eric G. Adelberger (University of Washington, Seattle), James Battat (Massachusetts Institute of Technology), Douglas Currie (University of Maryland, College Park), William M. Folkner (Jet Propulsion Laboratory), Jens Gundlach (University of Washington, Seattle), Stephen M. Merkowitz (Goddard Space Flight Center), Kenneth L. Nordtvedt (Northwest Analysis), Robert D. Reasenberg (Harvard-Smithsonian Center for Astrophysics), Irwin I. Shapiro (Harvard-Smithsonian Center for Astrophysics), Michael Shao (Jet Propulsion Laboratory), Christopher W. Stubbs (Harvard University), Massimo Tinto (Jet Propulsion Laboratory), James G. Williams (Jet Propulsion Laboratory), Nan Yu (Jet Propulsion Laboratory)

Date: 17 Feb 2009

Abstract: The recent discovery of "dark energy" has challenged Einstein's general theory of relativity as a complete model for our macroscopic universe. From a theoretical view, the challenge is even stronger: general relativity clearly does not extend to the very small, where quantum mechanics holds sway. Fundamental physics models thus require some major revisions. We must explore deeper to both constrain and inspire this needed new physics. In the realm of the solar-system, we can effectively probe for small deviations from the predictions of general relativity: Technology now offers a wide range of opportunities to pursue experiments with accuracies orders of magnitude better than yet achieved. We describe both the relevant theoretical backgrounds and the opportunities for far more accurate solar system experiments.

Feb 19, 2009

0902.3004 (/preprints)
2009-02-19, 08:42 

[0902.3144] Detecting the Cosmological Stochastic Background of Gravitational Waves with FastICA

Authors: L. Izzo, S. Capozziello, M. De Laurentis

Date: 18 Feb 2009

Abstract: We show that the stochastic background of gravitational waves, produced in the early cosmological epochs, strictly depends on the assumed theory of gravity. In particular, the specific form of the function f(R), where R is the Ricci scalar, is related to the evolution and the production mechanism of gravitational waves. Using a neural network algorithm which only requires non-Gaussian nature and independence of the input signals we conclude that, in order to detect a CSB signal, the interferometric sensitivity of detector like VIRGO will be improved.

Feb 19, 2009

0902.3144 (/preprints)
2009-02-19, 08:42 

[0902.2720] Gravitational-wave extraction from neutron-star oscillations

Authors: Sebastiano Bernuzzi, Luca Baiotti, Giovanni Corvino, Roberto De Pietri, Alessandro Nagar

Date: 16 Feb 2009

Abstract: We compare different gravitational-wave extraction methods used in three-dimensional nonlinear simulations against linear simulations of perturbations of spherical spacetimes with matter. We present results from fully general-relativistic simulations of a system composed by an oscillating and non-rotating star emitting gravitational radiation. Results about the onset of non-linear effects are also shown.

Feb 17, 2009

0902.2720 (/preprints)
2009-02-17, 12:07 

[0902.1287] Discontinuous Galerkin method for computing gravitational waveforms from extreme mass ratio binaries

Authors: Scott E. Field (1), Jan S. Hesthaven (1), Stephen R. Lau (1 and 2) ((1) Brown, (2) New Mexico)

Date: 8 Feb 2009

Abstract: Gravitational wave emission from extreme-mass-ratio binaries (EMRBs) should be detectable by the joint NASA-ESU LISA project, spurring interest in analytical and numerical methods for investigating EMRBs. We describe a discontinuous Galerkin (dG) method for solving the distributionally forced 1+1 wave equations which arise when modeling EMRBs via the perturbation theory of Schwarzschild blackholes. Despite the presence of jump discontinuities in the relevant polar and axial gravitational "master functions", our dG method achieves global spectral accuracy, provided that we know the instantaneous position, velocity, and acceleration of the small particle. Here these variables are known, since we assume that the particle follows a timelike geodesic of the Schwarzschild geometry. We document the results of several numerical experiments testing our method, and discuss the possible incorporation of radiation reaction in the model.

Feb 10, 2009

0902.1287 (/preprints)
2009-02-10, 11:25 

[0902.1127] Binary black hole evolutions of approximate puncture initial data

Authors: Tanja Bode, Pablo Laguna, Deirdre M. Shoemaker, Ian Hinder, Frank Herrmann, Birjoo Vaishnav

Date: 6 Feb 2009

Abstract: Approximate solutions to the Einstein field equations are a valuable tool to investigate gravitational phenomena. An important aspect of any approximation is to investigate and quantify its regime of validity. We present a study that evaluates the effects that approximate puncture initial data, based on "skeleton" solutions to the Einstein constraints as proposed by Faye et al. [PRD 69, 124029 (2004)], have on numerical evolutions. Using data analysis tools, we assess the effectiveness of these constraint-violating initial data and show that the matches of waveforms from skeleton data with the corresponding waveforms from constraint-satisfying initial data are > 0.97 when the total mass of the binary is > 40M(solar). In addition, we demonstrate that the differences between the skeleton and the constraint-satisfying initial data evolutions, and thus waveforms, are due to negative Hamiltonian constraint violations present in the skeleton initial data located in the vicinity of the punctures. During the evolution, the skeleton data develops both Hamiltonian and momentum constraint violations that decay with time, with the binary system relaxing to a constraint-satisfying solution with black holes of smaller mass and thus different dynamics.

Feb 09, 2009

0902.1127 (/preprints)
2009-02-09, 09:17 

[0901.4936] Estimating the parameters of non-spinning binary black holes using ground-based gravitational-wave detectors: Statistical errors

Authors: P. Ajith, Sukanta Bose

Date: 30 Jan 2009

Abstract: (Abridged): We assess the statistical errors in estimating the parameters of non-spinning black-hole binaries using ground-based gravitational-wave detectors. While past assessments were based on only the inspiral/ring-down pieces of the coalescence signal, the recent progress in analytical and numerical relativity enables us to make more accurate projections using "complete" inspiral-merger-ringdown waveforms. We employ the Fisher matrix formalism to estimate how accurately the source parameters will be measurable using a single interferometer as well as a network of interferometers. Those estimates are further vetted by Monte-Carlo simulations. We find that the parameter accuracies of the complete waveform are, in general, significantly better than those of just the inspiral waveform in the case of binaries with total mass M > 20 M_sun. For the case of the Advanced LIGO detector, parameter estimation is the most accurate in the M=100-200 M_sun range. For an M=100M_sun system, the errors in measuring the total mass and the symmetric mass-ratio are reduced by an order of magnitude or more compared to inspiral waveforms. For binaries located at a luminosity distance d_L and observed with the Advanced LIGO--Advanced Virgo network, the sky-position error varies widely across the sky: For M=100M_sun systems at d_L=1Gpc, this variation ranges from ~0.01 square-degrees to one square-degree, with an average value of ~0.1 square-degrees. This is more than forty times better than the average sky-position accuracy of inspiral waveforms at this mass-range. The error in estimating d_L is dominated by the error in measuring the wave's polarization and is ~43% for low-mass binaries and ~23% for high-mass binaries located at d_L=1Gpc.

Feb 06, 2009

0901.4936 (/preprints)
2009-02-06, 09:17 

[0902.0307] Searching for binary coalescences with inspiral templates: Detection and parameter estimation

Authors: Benjamin Farr, Stephen Fairhurst, B.S. Sathyaprakash

Date: 2 Feb 2009

Abstract: There has been remarkable progress in numerical relativity recently. This has led to the generation of gravitational waveform signals covering what has been traditionally termed the three phases of the coalescence of a compact binary - the inspiral, merger and ringdown. In this paper, we examine the usefulness of inspiral only templates for both detection and parameter estimation of the full coalescence waveforms generated by numerical relativity simulations. To this end, we deploy as search templates waveforms based on the effective one-body waveforms terminated at the light-ring as well as standard post-Newtonian waveforms. We find that both of these are good for detection of signals. Parameter estimation is good at low masses, but degrades as the mass of the binary system increases.

Feb 06, 2009

0902.0307 (/preprints)
2009-02-06, 09:16 

[0901.4955] Accurate evolutions of inspiralling neutron-star binaries: assessment of the truncation error

Authors: Luca Baiotti, Bruno Giacomazzo, Luciano Rezzolla

Date: 30 Jan 2009

Abstract: We have recently presented an investigation in full general relativity of the dynamics and gravitational-wave emission from binary neutron stars which inspiral and merge, producing a black hole surrounded by a torus (see arXiv:0804.0594). We here discuss in more detail the convergence properties of the results presented in arXiv:0804.0594 and, in particular, the deterioration of the convergence rate at the merger and during the survival of the merged object, when strong shocks are formed and turbulence develops. We also show that physically reasonable and numerically convergent results obtained at low-resolution suffer however from large truncation errors and hence are of little physical use. We summarize our findings in an "error budget", which includes the different sources of possible inaccuracies we have investigated and provides a first quantitative assessment of the precision in the modelling of compact fluid binaries.

Feb 06, 2009

0901.4955 (/preprints)
2009-02-06, 09:16 

[0902.0368] A Bayesian Approach to the Detection Problem in Gravitational Wave Astronomy

Authors: Tyson B. Littenberg, Neil J. Cornish

Date: 2 Feb 2009

Abstract: The analysis of data from gravitational wave detectors can be divided into three phases: search, characterization, and evaluation. The evaluation of the detection - determining whether a candidate event is astrophysical in origin or some artifact created by instrument noise - is a crucial step in the analysis. The on-going analyses of data from ground based detectors use variants of the frequentist Neyman-Pearson criterion to set detection thresholds based on signal injections and time-slides of the data. These techniques frame the detection problem in terms of an artificial, infinite collection of trials, and do not take into account the particular character of the data in question. Moreover, these techniques are ill suited to addressing more complex problems such as teasing individual sources from the signal rich data streams of future space based gravitational wave detectors. Here we argue that the detection problem may best be addressed in a Bayesian framework, and demonstrate an "end-to-end" solution based on the Parallel Tempered Markov Chain Monte Carlo algorithm and thermodynamic integration of the model evidence. As a demonstration we consider the detection problem of selecting between models describing the data as instrument noise, or instrument noise plus the signal from a single compact galactic binary. The evidence ratios, or Bayes factors, computed by our end-to-end algorithm are found to be in close agreement with those computed using a Reversible Jump Markov Chain Monte Carlo algorithm.

Feb 06, 2009

0902.0368 (/preprints)
2009-02-06, 09:15 

[0902.0136] An improved analytical description of inspiralling and coalescing black-hole binaries

Authors: Thibault Damour, Alessandro Nagar

Date: 2 Feb 2009

Abstract: We present an analytical formalism, within the Effective-One-Body framework, which predicts gravitational-wave signals from inspiralling and coalescing black-hole binaries that agree, within numerical errors, with the results of the currently most accurate numerical relativity simulations for several different mass ratios. We think that our formalism opens a realistic possibility of constructing a sufficiently accurate, large bank of gravitational wave templates, as needed both for detection and data analysis of (non spinning) coalescing binary black holes.

Feb 06, 2009

0902.0136 (/preprints)
2009-02-06, 09:15 

[0902.0573] Gravitational self-force correction to the innermost stable circular orbit of a Schwarzschild black hole

Authors: Leor Barack, Norichika Sago

Date: 3 Feb 2009

Abstract: The innermost stable circular orbit (ISCO) of a test particle around a Schwarzschild black hole of mass $M$ is located at $r_{\rm isco}=6M G/cˆ2$ (Schwarzschild coordinate radius). If the particle is endowed with mass $\mu(\ll M)$, it experiences a gravitational self-force whose conservative piece alters the location of the ISCO. Here we calculate the resulting shifts $\Delta r_{\rm isco}$ and $\Delta\Omega_{\rm isco}$ in the ISCO's radius and frequency, at leading order in the mass ratio $\mu/M$. We obtain $\Delta r_{\rm isco}=-3.27 \mu G/cˆ2$ (in the Lorenz gauge) and $\Delta\Omega_{\rm isco}/\Omega_{\rm isco}=0.487 \mu/M$ (gauge invariant). We discuss the implications of our result within the context of extreme mass-ratio binary inspirals.

Feb 06, 2009

0902.0573 (/preprints)
2009-02-06, 09:15 

[0902.0790] Effective-one-body waveforms calibrated to numerical relativity simulations: coalescence of non-spinning, equal-mass black holes

Authors: Alessandra Buonanno, Yi Pan, Harald P. Pfeiffer, Mark A. Scheel, Luisa T. Buchman, Lawrence E. Kidder

Date: 4 Feb 2009

Abstract: We calibrate the effective-one-body (EOB) model to an accurate numerical simulation of an equal-mass, non-spinning binary black-hole coalescence produced by the Caltech-Cornell collaboration. Aligning the EOB and numerical waveforms at low frequency over a time interval of ~1000M, and taking into account the uncertainties in the numerical simulation, we investigate the significance and degeneracy of the EOB adjustable parameters during inspiral, plunge and merger, and determine the minimum number of EOB adjustable parameters that achieves phase and amplitude agreements on the order of the numerical error. We find that phase and fractional amplitude differences between the numerical and EOB values of the dominant gravitational wave mode h_{22} can be reduced to 0.02 radians and 2%, respectively, until a time 26 M before merger, and to 0.1 radians and 10%, at a time 16M after merger (during ringdown), respectively. Using LIGO, Enhanced LIGO and Advanced LIGO noise curves, we find that the overlap between the EOB and the numerical h_{22}, maximized only over the initial phase and time of arrival, is larger than 0.999 for equal-mass binary black holes with total mass 30-150 Msun. In addition to the leading gravitational mode (2,2), we compare the dominant subleading modes (4,4) and (3,2) and find phase and amplitude differences on the order of the numerical error. We also determine the mass-ratio dependence of one of the EOB adjustable parameters by fitting to numerical {\it inspiral} waveforms for black-hole binaries with mass ratios 2:1 and 3:1. These results improve and extend recent successful attempts aimed at providing gravitational-wave data analysts the best analytical EOB model capable of interpolating accurate numerical simulations.

Feb 06, 2009

0902.0790 (/preprints)
2009-02-06, 09:13