[0804.4816] A geometric algorithm for efficient coincident detection of gravitational waves

Authors: C.A.K. Robinson, B.S. Sathyaprakash, Anand S. Sengupta

Date: 30 Apr 2008

Abstract: Data from a network of gravitational wave detectors can be analyzed in coincidence to increase detection confidence and reduce non-stationarity of the background. We propose and explore a geometric algorithm to combine the data from a network of detectors. The algorithm makes optimal use of the variances and covariances that exist amongst the different parameters of a signal in a coincident detection of events. The new algorithm essentially associates with each trigger ellipsoidal regions in parameter space defined by the covariance matrix. Triggers from different detectors are deemed to be in coincidence if their ellipsoids have a non-zero overlap. Compared to an algorithm that uses uncorrelated windows separately for each of the signal parameters, the new algorithm greatly reduces the background rate thereby increasing detection efficiency at a given false alarm rate.

abs pdf

Apr 30, 2008

0804.4816 (/preprints)
2008-04-30, 19:02 [edit]


[0804.4184] High-accuracy numerical simulation of black-hole binaries: Computation of the gravitational-wave energy flux and comparisons with post-Newtonian approximants

Authors: Michael Boyle, Alessandra Buonanno, Lawrence E. Kidder, Abdul H. Mroué, Yi Pan, Harald P. Pfeiffer, Mark A. Scheel

Date: 25 Apr 2008

Abstract: Expressions for the gravitational wave (GW) energy flux and center-of-mass energy of a compact binary are integral building blocks of post-Newtonian (PN) waveforms. In this paper, we compute the GW energy flux and GW frequency derivative from a highly accurate numerical simulation of an equal-mass, non-spinning black hole binary. We also estimate the (derivative of the) center-of-mass energy from the simulation by assuming energy balance. We compare these quantities with the predictions of various PN approximants (adiabatic Taylor and Pade models; non-adiabatic effective-one-body (EOB) models). We find that Pade summation of the energy flux does not accelerate the convergence of the flux series; nevertheless, the Pade flux is markedly closer to the numerical result for the whole range of the simulation (about 30 GW cycles). Taylor and Pade models overestimate the increase in flux and frequency derivative close to merger, whereas EOB models reproduce more faithfully the shape of and are closer to the numerical flux, frequency derivative and derivative of energy. We also compare the GW phase of the numerical simulation with Pade and EOB models. Matching numerical and untuned 3.5 PN order waveforms, we find that the phase difference accumulated until $M \omega = 0.1$ is -0.12 radians for Pade approximants, and 0.50 (-0.28) radians for an EOB approximant with Keplerian (non-Keplerian) flux. We fit free parameters within the EOB models to minimize the phase difference, and discover degeneracies among these parameters. By tuning pseudo 4PN order coefficients in the radial potential or in the flux, or, if present, the location of the pole in the flux, we find that the accumulated phase difference can be reduced - if desired - to much less than the estimated numerical phase error (0.04 radians).

abs pdf

Apr 29, 2008

0804.4184 (/preprints)
2008-04-29, 09:20 [edit]


[0804.4144] Search for a stochastic gravitational-wave signal in the second round of the Mock LISA Data Challenges

Authors: E. L. Robinson, J. D. Romano, A. Vecchio

Date: 25 Apr 2008

Abstract: The analysis method currently proposed to search for isotropic stochastic radiation of primordial or astrophysical origin with the Laser Interferometer Space Antenna (LISA) relies on the combined use of two LISA channels, one of which is insensitive to gravitational waves, such as the symmetrised Sagnac. For this method to work, it is essential to know how the instrumental noise power in the two channels are related to one another; however, no quantitative estimates of this key information are available to date. The purpose of our study is to assess the performance of the symmetrised Sagnac method for different levels of prior information regarding the instrumental noise. We develop a general approach in the framework of Bayesian inference and an end-to-end analysis algorithm based on Markov Chain Monte Carlo methods to compute the posterior probability density functions of the relevant model parameters. We apply this method to data released as part of the second round of the Mock LISA Data Challenges. For the selected (and somewhat idealised) cases considered here, we find that a prior uncertainty of a factor ~2 in the ratio between the power of the instrumental noise contributions in the two channels allows for the detection of isotropic stochastic radiation. More importantly, we provide a framework for more realistic studies of LISA's performance and development of analysis techniques in the context of searches for stochastic signals.

abs pdf

Apr 28, 2008

0804.4144 (/preprints)
2008-04-28, 08:36 [edit]


[0804.3853] Modelling coloured noise

Authors: Christian Röver (Max-Planck-Institut für Gravitationsphysik, Hannover, Germany), Renate Meyer (The University of Auckland, Auckland, New Zealand), Nelson Christensen (Carleton College, Northfield, MN, USA)

Date: 24 Apr 2008

Abstract: This paper introduces a novel approach to modelling non-white residual noise in discrete time series. We present a Markov chain Monte Carlo (MCMC) algorithm for combined posterior inference on signal and noise parameters. By choosing a conjugate prior distribution for the noise parameters, the additional Gibbs sampling steps have a particularly simple form and are easy to implement as well as fast to run. Furthermore, the sampling-based approach allows for easy inference on the autocovariance function. The model is illustrated using a well-known sunspot dataset as well as a simulated dataset of a chirp signal embedded in non-Normal, coloured noise where the spectrum is regarded as a nuisance parameter.

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Apr 28, 2008

0804.3853 (/preprints)
2008-04-28, 08:36 [edit]


[0804.4029] Markov chain Monte Carlo searches for Galactic binaries in Mock LISA Data Challenge 1B data sets

Authors: Miquel Trias, Alberto Vecchio, John Veitch

Date: 24 Apr 2008

Abstract: We are developing a Bayesian approach based on Markov chain Monte Carlo techniques to search for and extract information about white dwarf binary systems with the Laser Interferometer Space Antenna (LISA). Here we present results obtained by applying an initial implementation of this method to some of the data sets released in Round 1B of the Mock LISA Data Challenges. For Challenges 1B.1.1a and 1b the signals were recovered with parameters lying within the 95.5% posterior probability interval and the correlation between the true and recovered waveform is in excess of 99%. Results were not submitted for Challenge 1B.1.1c due to some convergence problems of the algorithms, despite the signal was detected in a search over a 2 mHz band.

abs pdf

Apr 28, 2008

0804.4029 (/preprints)
2008-04-28, 08:35 [edit]


[0804.3390] Effects of Prior Assumptions on Bayesian Estimates of Inflation Parameters, and the expected Gravitational Waves Signal from Inflation

Authors: Wessel Valkenburg, Lawrence M. Krauss, Jan Hamann

Date: 22 Apr 2008

Abstract: In this work we explore the effect of choosing flat priors on different parameterizations on the estimation of the tensor-to-scalar ratio and other parameters describing inflation. We show that a flat prior on the scale of inflation does not correspond to a flat prior on the tensor-to-scalar ratio, and that current data is not strong enough to render parameter estimation parameterization independent. Most importantly, we show that a flat prior on the scale of inflation raises the predicted tensor contribution, leading to a mild, yet non-zero 68 % c.l. lower bound on tensor perturbations from existing data. Which prior to choose remains for the moment a matter of taste. However this work provides more reason for optimism with respect to the possibility of future detection of primordial gravitational waves.

abs pdf

Apr 25, 2008

0804.3390 (/preprints)
2008-04-25, 09:19 [edit]


[0804.3806] Gravito-Magnetism in one-body and two-body systems: Theory and Experiments

Authors: R. F. O'Connell

Date: 23 Apr 2008

Abstract: We survey theoretical and experimental/observational results on general-relativistic spin (rotation) effects in binary systems. A detailed discussion is given of the two-body Kepler problem and its first post-Newtonian generalization, including spin effects. Spin effects result from gravitational spin-orbit and spin-spin interactions (analogous to the corresponding case in quantum electrodynamics) and these effects are shown to manifest themselves in two ways: (a) precession of the spinning bodies per se and (b) precession of the orbit (which is further broke down into precessions of the argument of the periastron, the longitude of the ascending node and the inclination of the orbit). We also note the ambiguity that arises from use of the terminology frame-dragging, de Sitter precession and Lense-Thirring precession, in contrast to the unambiguous reference to spin-orbit and spin-spin precessions. Turning to one-body experiments, we discuss the recent results of the GP-B experiment, the Ciufolini-Pavlis Lageos experiment and lunar-laser ranging measurements (which actually involve three bodies). Two-body systems inevitably involve astronomical observations and we survey results obtained from the first binary pulsar system, a more recently discovered binary system and, finally, the highly significant discovery of a double-pulsar binary system.

abs pdf

Apr 25, 2008

0804.3806 (/preprints)
2008-04-25, 09:18 [edit]


[0804.3787] Initial data for black hole-neutron star binaries: a flexible, high-accuracy spectral method

Authors: Francois Foucart, Lawrence E. Kidder, Harald P. Pfeiffer, Saul A. Teukolsky

Date: 23 Apr 2008

Abstract: We present a new numerical scheme to solve the initial value problem for black hole-neutron star binaries. This method takes advantage of the flexibility and fast convergence of a multidomain spectral representation of the initial data to construct high-accuracy solutions at a relatively low computational cost. We provide convergence tests of the method for both isolated neutron stars and irrotational binaries. In the second case, we show that we can resolve the small inconsistencies that are part of the quasi-equilibrium formulation, and that these inconsistencies are significantly smaller than observed in previous works. The possibility of generating a wide variety of initial data is also demonstrated through two new configurations inspired by results from binary black holes. First, we show that choosing a modified Kerr-Schild conformal metric instead of a flat conformal metric allows for the construction of quasi-equilibrium binaries with a spinning black hole. Second, we construct binaries in low-eccentricity orbits, which are a better approximation to astrophysical binaries than quasi-equilibrium systems.

abs pdf

Apr 23, 2008

0804.3787 (/preprints)
2008-04-23, 18:27 [edit]


[0804.3393] Proposed search method for gravitational waves from PKS 2155-304 and other blazar flares

Authors: Shantanu Desai, Kazuhiro Hayama, Soumya Mohanty, Malik Rakhmanov, Tiffany Summerscales, Sanichiro Yoshida

Date: 21 Apr 2008

Abstract: We motivate searches for gravitational waves from transient blazar flares with emphasis on PKS 2155-304. PKS 2155-304 is a blazar with redshift approximately equal to 0.12. On July 28 2006, the H.E.S.S. atmospheric Cherenkov telescopes detected an outburst of TeV gamma rays from this object lasting approximately two hours with total isotropic equivalent energy released in TeV gamma rays (without accounting for attenuation with infrared photons) approximately $10ˆ{45}$ ergs. During this period, the two LIGO detectors at Hanford and GEO were running and collecting science mode data. We propose to look for gravitational waves during this gamma-ray outburst with the RIDGE network analysis pipeline. Simulated detector noise is used to study the performance achievable by RIDGE in measuring possible gravitational wave signals associated with this event.

abs pdf

Apr 23, 2008

0804.3393 (/preprints)
2008-04-23, 10:30 [edit]


[0804.3323] Detection Strategies for Extreme Mass Ratio Inspirals

Authors: N. J. Cornish

Date: 21 Apr 2008

Abstract: The capture of compact stellar remnants by galactic black holes provides a unique laboratory for exploring the near horizon geometry of the Kerr spacetime. The gravitational radiation produced by these Extreme Mass Ratio Inspirals (EMRIs) encodes a detailed map of the black hole geometry, and the detection and characterization of these signals is a major science driver for the LISA observatory. The waveforms produced are very complex, and the signals need to be coherently tracked for hundreds to thousands of cycles to produce a detection, making EMRI signals one of the most challenging data analysis problems in all of gravitational wave astronomy. Estimates for the number of templates required to perform an optimal matched-filter search for these signals are astronomically large, and far out of reach of current computational resources. Here a sub-optimal, hierarchical approach to the EMRI detection problem is developed that employs a directed-stochastic search technique. The algorithm, dubbed Metropolis Hastings Monte Carlo (MHMC), is a close cousin of Markov Chain Monte Carlo and genetic algorithms. The utility of the MHMC approach is demonstrated using simulated data sets from the Mock LISA Data Challenge.

abs pdf

Apr 22, 2008

0804.3323 (/preprints)
2008-04-22, 09:44 [edit]


[0804.3322] A Constrained Metropolis-Hastings Search for EMRIs in the Mock LISA Data Challenge 1B

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

Date: 21 Apr 2008

Abstract: We describe a search for the EMRI sources in the Round 1B Mock LISA Data Challenge data sets. The search algorithm is a Monte-Carlo search based on the Metropolis-Hastings algorithm, but also incorporates simulated, thermostated and time annealing, plus a harmonic identification stage designed to reduce the chance of the chain locking onto secondary maxima. In this paper, we focus on describing the algorithm that we have been developing. We give the results of the search of the Round 1B data, although parameter recovery has improved since that deadline. Finally, we describe several modifications to the search pipeline that we are currently investigating for incorporation in future searches.

abs pdf

Apr 22, 2008

0804.3322 (/preprints)
2008-04-22, 09:43 [edit]


[0804.3274] A hierarchical search for gravitational waves from supermassive black hole binary mergers

Authors: I.W. Harry, S. Fairhurst, B.S. Sathyaprakash

Date: 21 Apr 2008

Abstract: We present a method to search for gravitational waves from coalescing supermassive binary black holes in LISA data. The search utilizes the $\mathcal{F}$-statistic to maximize over, and determine the values of, the extrinsic parameters of the binary system. The intrinsic parameters are searched over hierarchically using stochastically generated multi-dimensional template banks to recover the masses and sky locations of the binary. We present the results of this method applied to the mock LISA data Challenge 1B data set.

abs pdf

Apr 22, 2008

0804.3274 (/preprints)
2008-04-22, 09:43 [edit]


[0804.3075] Blandford's Argument: The Strongest Continuous Gravitational Wave Signal

Authors: B. Knispel, B. Allen

Date: 18 Apr 2008

Abstract: For a uniform population of neutron stars whose spin-down is dominated by the emission of gravitational radiation, an argument by Blandford states that the expected gravitational wave amplitude of the nearest source is independent of the deformation and rotation frequency of the objects. Recent work has improved and extended this argument to set upper limits on the expected amplitude from neutron stars which also emit electromagnetic radiation. We restate these argments in a more general framework, and simulate the evolution of such a population of stars in the gravitational potential of our Galaxy. The simulations allow us to test the assumptions of Blandford's argument on a realistic model of our Galaxy. We show that the two key assumptions of the argument (two-dimensionality of the spatial distribution and a steady-state frequency distribution) are in general not fulfilled. The effective scaling dimension of the spatial distribution of neutron stars is significantly larger than two, and for frequencies detectable by terrestrial instruments the frequency distribution is not in a steady state unless the ellipticity is unrealistically large. Thus, in the cases of most interest, the maximum expected gravitational wave amplitude does have a strong dependence on the deformation and rotation frequency of the population. The results strengthen the previous upper limits on the expected gravitational wave amplitude from neutron stars.

abs pdf

Apr 21, 2008

0804.3075 (/preprints)
2008-04-21, 09:45 [edit]


[0804.1797] Chern-Simons Modified Gravity as a Torsion Theory and its Interaction with Fermions

Authors: Stephon Alexander, Nicolas Yunes

Date: 10 Apr 2008

Abstract: We study the tetrad formulation of Chern-Simons (CS) modified gravity, which adds a Pontryagin term to the Einstein-Hilbert action with a spacetime-dependent coupling field. We first verify that CS modified gravity leads to a theory with torsion, where this tensor is given by an antisymmetric product of the Riemann tensor and derivatives of the CS coupling. We then calculate the torsion in the far field of a weakly gravitating source within the parameterized post-Newtonian formalism, and specialize the result to Earth. We find that CS torsion vanishes only if the coupling vanishes, thus generically leading to a modification of gyroscopic precession, irrespective of the coupling choice. Perhaps most interestingly, we couple fermions to CS modified gravity via the standard Dirac action and find that these further correct the torsion tensor. Such a correction leads to two new results: (i) a generic enhancement of CS modified gravity by the Dirac equation and axial fermion currents; (ii) a new two-fermion interactions, mediated by an axial current and the CS correction. We conclude with a discussion of the consequences of these results in particle detectors and realistic astrophysical systems.

abs pdf

Apr 15, 2008

0804.1797 (/preprints)
2008-04-15, 10:25 [edit]


[0804.2103] Minimizing the kinematical effects on LISA's performance

Authors: Ioannis Deligiannis, Theocharis A. Apostolatos

Date: 14 Apr 2008

Abstract: Proper tuning of the orbital characteristics of the three spacecrafts that constitute the usual triangular configuration of the space-borne gravitational-wave detector LISA, could minimize the breathing mode of its arm-lengths. Since the three spacecrafts form three pairs of interferometric arms, we have the freedom to minimize whichever combination of arm-length variations that might be useful in signal analysis. Thus for any kind of time delay interferometry (TDI), that is chosen to be used in analysing the data, the optimal orbital characteristics could be chosen accordingly, so as to enhance the performance of the gravitational wave detector.

abs pdf

Apr 15, 2008

0804.2103 (/preprints)
2008-04-15, 10:24 [edit]


[0804.1161] Monte-Carlo and Bayesian techniques in gravitational wave burst data analysis

Authors: Antony C. Searle

Date: 7 Apr 2008

Abstract: Monte-Carlo simulations are used in the gravitational wave burst detection community to demonstrate and compare the properties of different search techniques. We note that every Monte-Carlo simulation has a corresponding optimal search technique according to both the non-Bayesian Neyman-Pearson criterion and the Bayesian approach, and that this optimal search technique is the Bayesian statistic. When practical, we recommend deriving the optimal statistic for a credible Monte-Carlo simulation, rather than testing ad hoc statistics against that simulation.

abs pdf

Apr 08, 2008

0804.1161 (/preprints)
2008-04-08, 17:56 [edit]


[0804.1127] Tests of Relativistic Gravity in Space: Recent Progress and Future Directions

Authors: Slava G. Turyshev

Date: 7 Apr 2008

Abstract: We review the foundations of Einstein's general theory of relativity, discuss recent progress in the tests of relativistic gravity, and present motivations for new generation of high-accuracy gravitational experiments. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential of the recently proposed gravitational experiments.

abs pdf

Apr 08, 2008

0804.1127 (/preprints)
2008-04-08, 17:55 [edit]


[0804.1084] Improved time-frequency analysis of extreme-mass-ratio inspiral signals in mock LISA data

Authors: Jonathan R Gair, Ilya Mandel, Linqing Wen

Date: 7 Apr 2008

Abstract: The planned Laser Interferometer Space Antenna (LISA) is expected to detect gravitational wave signals from ~100 extreme-mass-ratio inspirals (EMRIs) of stellar-mass compact objects into massive black holes. The long duration and large parameter space of EMRI signals makes data analysis for these signals a challenging problem. One approach to EMRI data analysis is to use time-frequency methods. This consists of two steps: (i) searching for tracks from EMRI sources in a time-frequency spectrogram, and (ii) extracting parameter estimates from the tracks. In this paper we discuss the results of applying these techniques to the latest round of the Mock LISA Data Challenge, Round 1B. This analysis included three new techniques not used in previous analyses: (i) a new Chirp-based Algorithm for Track Search for track detection; (ii) estimation of the inclination of the source to the line of sight; (iii) a Metropolis-Hastings Monte Carlo over the parameter space in order to find the best fit to the tracks.

abs pdf

Apr 07, 2008

0804.1084 (/preprints)
2008-04-07, 21:02 [edit]


[0804.1075] Computational Efficiency of Frequency-- and Time--Domain Calculations of Extreme Mass--Ratio Binaries: Equatorial Orbits

Authors: Jonathan L. Barton, David J. Lazar, Daniel J. Kennefick, Gaurav Khanna, Lior M. Burko

Date: 7 Apr 2008

Abstract: Gravitational waveforms and fluxes from extreme mass--ratio inspirals can be computed using time--domain methods with accuracy that is fast approaching that of frequency--domain methods. We study in detail the computational efficiency of these methods for equatorial orbits of fast spinning Kerr black holes, and find the number of modes needed in either method --as functions of the orbital parameters-- in order to achieve a desired accuracy level. We then estimate the total computation time and argue that for high eccentricity orbits the time--domain approach is more efficient computationally. We suggest that in practice low--$m$ modes are computed using the frequency--domain approach, and high--$m$ modes are computed using the time--domain approach, where $m$ is the azimuthal mode number.

abs pdf

Apr 07, 2008

0804.1075 (/preprints)
2008-04-07, 21:02 [edit]


[0804.1036] Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector

Authors: A. Freise, S. Chelkowski, S. Hild, W. Del Pozzo, A. Perreca, A. Vecchio

Date: 7 Apr 2008

Abstract: The upcoming European design study ‘Einstein gravitational wave Telescope’ represents the first step towards a substantial, international effort for the design of a third-generation interferometric gravitational wave detector. It is generally believed that third generation instruments cannot be installed into existing infrastructures but will require a new search for optimal detector sites. Consequently, the detector design will be subject to fewer constraints than the on-going design of the second generation instruments. In particular, it will be prudent to investigate alternatives to the traditional L-shaped Michelson interferometer. In this article, we review an old proposal to use three Michelson interferometers in a triangular configuration. We use this example of a triple Michelson interferometer to clarify the terminology and will put this idea into the context of more recent research on interferometer technologies. Furthermore the benefits of a triangular detector will be used to motivate this design as a good starting point for a more detailed research effort towards a third-generation gravitational wave detector.

abs pdf

Apr 07, 2008

0804.1036 (/preprints)
2008-04-07, 21:01 [edit]


[0804.0628] Wormholes and trumpets: the Schwarzschild spacetime for the moving-puncture generation

Authors: Mark Hannam, Sascha Husa, Frank Ohme, Bernd Bruegmann, Niall O'Murchadha

Date: 3 Apr 2008

Abstract: We expand upon our previous analysis of numerical moving-puncture simulations of the Schwarzschild spacetime. We present a derivation of the family of analytic stationary 1+log foliations of the Schwarzschild solution, and outline a transformation to isotropic-like coordinates. We discuss in detail the numerical evolution of standard Schwarzschild puncture data, and the new time-independent 1+log data. Finally, we demonstrate that the moving-puncture method can locate the appropriate stationary geometry in a robust manner when a numerical code alternates between two forms of 1+log slicing during a simulation.

abs pdf

Apr 06, 2008

0804.0628 (/preprints)
2008-04-06, 21:16 [edit]


[0804.0594] Accurate evolutions of inspiralling neutron-star binaries: prompt and delayed collapse to black hole

Authors: Luca Baiotti, Bruno Giacomazzo, Luciano Rezzolla

Date: 3 Apr 2008

Abstract: Binary neutron-star (BNS) systems represent primary sources for the gravitational-wave (GW) detectors. We present a systematic investigation in full GR of the dynamics and GW emission from BNS which inspiral and merge, producing a black hole (BH) surrounded by a torus. Our results represent the state of the art from several points of view: (i) We use HRSC methods for the hydrodynamics equations and high-order finite-differencing techniques for the Einstein equations; (ii) We employ AMR techniques with "moving boxes"; (iii) We use as initial data BNSs in irrotational quasi-circular orbits; (iv) We exploit the isolated-horizon formalism to measure the properties of the BHs produced in the merger; (v) Finally, we use two approaches, based either on gauge-invariant perturbations or on Weyl scalars, to calculate the GWs. These techniques allow us to perform accurate evolutions on timescales never reported before (ie ~30 ms) and to provide the first complete description of the inspiral and merger of a BNS leading to the prompt or delayed formation of a BH and to its ringdown. We consider either a polytropic or an ideal fluid EOS and show that already with this idealized EOSs a very interesting phenomenology emerges. In particular, we show that while high-mass binaries lead to the prompt formation of a rapidly rotating BH surrounded by a dense torus, lower-mass binaries give rise to a differentially rotating NS, which undergoes large oscillations and emits large amounts of GWs. Eventually, also the NS collapses to a rotating BH surrounded by a torus. Finally, we also show that the use of a non-isentropic EOS leads to significantly different evolutions, giving rise to a delayed collapse also with high-mass binaries, as well as to a more intense emission of GWs and to a geometrically thicker torus.

abs pdf

Apr 03, 2008

0804.0594 (/preprints)
2008-04-03, 18:23 [edit]


[0804.0492] LISA parameter estimation of supermassive black holes

Authors: Miquel Trias, Alicia M. Sintes

Date: 3 Apr 2008

Abstract: We study parameter estimation of supermassive black holes in the range $10ˆ5-10ˆ8\Ms$ by LISA using the inspiral full post-Newtonian gravitational waveforms, and we compare the results with those arising from the commonly used restricted post-Newtonian approximation. The analysis shows that for observations of the last year before merger, the inclusion of the higher harmonics clearly improves the parameter estimation.

abs pdf

Apr 03, 2008

0804.0492 (/preprints)
2008-04-03, 18:22 [edit]


[0804.0332] The Effect of Higher Harmonic Corrections on the Detection of massive black hole binaries with LISA

Authors: Edward K. Porter, Neil J. Cornish

Date: 2 Apr 2008

Abstract: Massive black hole binaries are key targets for the space based gravitational wave interferometer LISA. Several studies have investigated how LISA observations could be used to constrain the parameters of these systems. Until recently, most of these studies have ignored the higher harmonic corrections to the waveforms. Here we analyze the effects of the higher harmonics in more detail by performing extensive Monte Carlo simulations. We pay particular attention to how the higher harmonics impact parameter correlations, and show that the additional harmonics help mitigate the impact of having two laser links fail, by allowing for an instantaneous measurement of the gravitational wave polarization with a single interferometer channel. By looking at parameter correlations we are able to explain why certain mass ratios provide dramatic improvements in certain parameter estimations, and illustrate how the improved polarization measurement improves the prospects for single interferometer operation.

abs pdf

Apr 02, 2008

0804.0332 (/preprints)
2008-04-02, 19:27 [edit]


[0804.0279] A Discrete Representation of Einstein's Geometric Theory of Gravitation: The Fundamental Role of Dual Tessellations in Regge Calculus

Authors: Jonathan R. McDonald, Warner A. Miller

Date: 2 Apr 2008

Abstract: In 1961 Tullio Regge provided us with a beautiful lattice representation of Einstein's geometric theory of gravity. This Regge Calculus (RC) is strikingly different from the more usual finite difference and finite element discretizations of gravity. In RC the fundamental principles of General Relativity are applied directly to a tessellated spacetime geometry. In this manuscript, and in the spirit of this conference, we reexamine the foundations of RC and emphasize the central role that the Voronoi and Delaunay lattices play in this discrete theory. In particular we describe, for the first time, a geometric construction of the scalar curvature invariant at a vertex. This derivation makes use of a new fundamental lattice cell built from elements inherited from both the 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 and more familiar hinge-based expression in RC (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. What is most striking to us is how naturally spacetime is represented by Voronoi and Delaunay structures and that the laws of gravity appear to be encoded locally on the lattice spacetime with less complexity than in the continuum, yet the continuum is recovered by convergence in mean. Perhaps these prominent features may enable us to transcend the details of any particular discrete model gravitation and yield clues to help us discover how we may begin to quantize this fundamental interaction.

abs pdf

Apr 02, 2008

0804.0279 (/preprints)
2008-04-02, 19:27 [edit]


[0804.0260] Next to Leading Order Spin(1)Spin(1) Effects in the Motion of Inspiralling Compact Binaries

Authors: Rafael A Porto, Ira Z. Rothstein

Date: 1 Apr 2008

Abstract: Using effective field theory techniques we compute the next to leading order Spin(1)Spin(1) terms in the potential of spinning compact objects at third Post-Newtonian order, including subleading self-induced finite size effects. This result represents the last ingredient to complete the relevant spin potentials to 3PN order from which the equations of motion follow via a canonical formalism. As an example we include the precession equation.

abs pdf

Apr 02, 2008

0804.0260 (/preprints)
2008-04-02, 19:26 [edit]


[physics/0407078] Mach's Principle

Authors: Herbert Lichtenegger, Bahram Mashhoon

Date: 14 Jul 2004

Abstract: We briefly review the history of Mach's principle and discuss its significance in the light of modern physics.

abs pdf

Apr 02, 2008

0407078 (/preprints/physics)
2008-04-02, 19:26 [edit]


[0803.4193] General relativistic simulations of magnetized binary neutron star mergers

Authors: Yuk Tung Liu, Stuart L. Shapiro, Zachariah B. Etienne, Keisuke Taniguchi (UIUC)

Date: 28 Mar 2008

Abstract: Binary neutron stars (NSNS) are expected to be among the leading sources of gravitational waves observable by ground-based laser interferometers and may be the progenitors of short-hard gamma ray bursts. We present a series of general relativistic NSNS coalescence simulations both for unmagnetized and magnetized stars. We adopt quasiequilibrium initial data for circular, irrotational binaries constructed in the conformal thin-sandwich (CTS) framework. We adopt the BSSN formulation for evolving the metric and a high-resolution shock-capturing scheme to handle the magnetohydrodynamics. Our simulations of unmagnetized binaries confirm the results of Shibata, Taniguchi and Uryu (2003). In cases in which the mergers result in a prompt collapse to a black hole, we are able to use puncture gauge conditions to extend the evolution and determine the mass of the material that forms a disk. We find that the disk mass is less than 2% of the total mass in all cases studied. We then add a small poloidal magnetic field to the initial configurations and study the subsequent evolution. For cases in which the remnant is a hypermassive neutron star, we see measurable differences in both the amplitude and phase of the gravitational waveforms following the merger. For cases in which the remnant is a black hole surrounded by a disk, the disk mass and the gravitational waveforms are about the same as the unmagnetized cases. Magnetic fields substantially affect the long-term, secular evolution of a hypermassive neutron star (driving ‘delayed collapse’) and an accretion disk around a nascent black hole.

abs pdf

Apr 02, 2008

0803.4193 (/preprints)
2008-04-02, 19:26 [edit]


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