[0911.4232] Third-and-a-half order post-Newtonian equations of motion for relativistic compact binaries using the strong field point particle limit

Authors: Yousuke Itoh

Date: 22 Nov 2009

Abstract: We report our rederivation of the equations of motion for relativistic compact binaries through the third-and-a-half post-Newtonian (3.5 PN) order approximation to general relativity using the strong field point particle limit to describe self-gravitating stars instead of the Dirac delta functional. The computation is done in harmonic coordinates. Our equations of motion describe the orbital motion of the binary consisting of spherically symmetric non-rotating stars. The resulting equations of motion fully agree with the 3.5 PN equations of motion derived in the previous works. We also show that the locally defined energy of the star has a simple relation with its mass up to the 3.5 PN order.

abs pdf

Nov 30, 2009

0911.4232 (/preprints)
2009-11-30, 12:53 [edit]


[0911.4939] Relativistic figures of equilibrium: from Maclaurin spheroids to Kerr black holes

Authors: Reinhard Meinel

Date: 25 Nov 2009

Abstract: Analytical and numerical results on equilibrium configurations of rotating fluid bodies within Einstein's theory of gravitation are reviewed. Particular emphasis is placed on continuous parametric transitions to black holes. In this connection the uniqueness of extremal Kerr black holes is discussed.

abs pdf

Nov 30, 2009

0911.4939 (/preprints)
2009-11-30, 12:52 [edit]


[0911.4718] Testing Properties of the Galactic Center Black Hole Using Stellar Orbits

Authors: David Merritt, Tal Alexander, Seppo Mikkola, Clifford M. Will

Date: 25 Nov 2009

Abstract: The spin and quadrupole moment of the supermassive black hole at the Galactic center can in principle be measured via astrometric monitoring of stars orbiting at milliparsec (mpc) distances, allowing tests of general relativistic "no-hair" theorems (Will 2008). One complicating factor is the presence of perturbations from other stars, which may induce orbital precession of the same order of magnitude as that due to general relativistic effects. The expected number of stars in this region is small enough that full N-body simulations can be carried out. We present the results of a comprehensive set of such simulations, which include a post-Newtonian treatment of spin-orbit effects. A number of possible models for the distribution of stars and stellar remnants are considered. We find that stellar perturbations are likely to obscure the signal due to frame-dragging for stars beyond ~0.5 mpc from the black hole, while measurement of the quadrupole moment is likely to require observation of stars inside ~0.2 mpc. A high fraction of stellar remnants, e.g. 10-Solar-mass black holes, in this region would make tests of GR problematic at all radii. We discuss the possibility of separating the effects of stellar perturbations from those due to GR.

abs pdf

Nov 30, 2009

0911.4718 (/preprints)
2009-11-30, 12:52 [edit]


[0911.5051] Random template placement and prior information

Authors: Christian Röver

Date: 26 Nov 2009

Abstract: In signal detection problems, one is usually faced with the task of searching a parameter space for peaks in the likelihood function which indicate the presence of a signal. Random searches have proven to be very efficient as well as easy to implement, compared e.g. to searches along regular grids in parameter space. Knowledge of the parameterised shape of the signal searched for adds structure to the parameter space, i.e., there are usually regions requiring to be densely searched while in other regions a coarser search is sufficient. On the other hand, prior information identifies the regions in which a search will actually be promising or may likely be in vain. Defining specific figures of merit allows one to combine both template metric and prior distribution and devise optimal sampling schemes over the parameter space. We show an example related to the gravitational wave signal from a binary inspiral event. Here the template metric and prior information are particularly contradictory, since signals from low-mass systems tolerate the least mismatch in parameter space while high-mass systems are far more likely, as they imply a greater signal-to-noise ratio (SNR) and hence are detectable to greater distances. The derived sampling strategy is implemented in a Markov chain Monte Carlo (MCMC) algorithm where it improves convergence.

abs pdf

Nov 30, 2009

0911.5051 (/preprints)
2009-11-30, 12:49 [edit]


[0911.5041] Effective One Body description of tidal effects in inspiralling compact binaries

Authors: Thibault Damour, Alessandro Nagar

Date: 27 Nov 2009

Abstract: The late part of the gravitational wave signal of binary neutron star inspirals can in principle yield crucial information on the nuclear equation of state via its dependence on relativistic tidal parameters. In the hope of analytically describing the gravitational wave phasing during the late inspiral (essentially up to contact) we propose an extension of the effective one body (EOB) formalism which includes tidal effects. We compare the prediction of this tidal-EOB formalism to recently computed nonconformally flat quasi-equilibrium circular sequences of binary neutron star systems. Our analysis suggests the importance of higher-order (post-Newtonian) corrections to tidal effects, even beyond the first post-Newtonian order, and their tendency to {\it significantly} increase the ‘effective tidal polarizability’ of neutron stars. We compare the EOB predictions to some recently advocated, nonresummed, post-Newtonian based (‘Taylor-T4’) description of the phasing of inspiralling systems. This comparison shows the strong sensitivity of the late-inspiral phasing to the choice of the analytical model, but raises the hope that a sufficiently accurate numerical--relativity--‘calibrated’ EOB model might give us a reliable handle on the nuclear equation of state

abs pdf

Nov 30, 2009

0911.5041 (/preprints)
2009-11-30, 12:47 [edit]


[0911.3175] LISA long-arm interferometry

Authors: James Ira Thorpe

Date: 16 Nov 2009

Abstract: The Laser Interferometer Space Antenna (LISA) will observe gravitational radiation in the milliHertz band by measuring picometer-level fluctuations in the distance between drag-free proof masses over baselines of approximately five million kilometers. The measurement over each baseline will be divided into three parts: two short-arm measurements between the proof masses and a fiducial point on their respective spacecraft, and a long-arm measurement between fiducial points on separate spacecraft. This work focuses on the technical challenges associated with these long-arm measurements and the techniques that have been developed to overcome them.

abs pdf

Nov 23, 2009

0911.3175 (/preprints)
2009-11-23, 09:07 [edit]


[0911.3535] Tidal deformability of neutron stars with realistic equations of state and their gravitational wave signatures in binary inspiral

Authors: Tanja Hinderer, Benjamin D. Lackey, Ryan N. Lang, Jocelyn S. Read

Date: 18 Nov 2009

Abstract: The early part of the gravitational wave signal of binary neutron star inspirals can potentially yield robust information on the nuclear equation of state. The influence of a star's internal structure on the waveform is characterized by a single parameter: the tidal deformability lambda, which measures the star's quadrupole deformation in response to the companion's perturbing tidal field. We calculate lambda for a wide range of equations of state and find that the value of lambda spans an order of magnitude for the range of equation of state models considered.
An analysis of the feasibility of discriminating between neutron star equations of state with gravitational wave observations of the early part of the inspiral reveals that the measurement error in lambda increases steeply with the total mass of the binary. Comparing the errors with the expected range of lambda, we find that Advanced LIGO observations of binaries at a distance of 100 Mpc will probe only unusually stiff equations of state, while the proposed Einstein Telescope is likely to see a clean tidal signature.

abs pdf

Nov 23, 2009

0911.3535 (/preprints)
2009-11-23, 09:06 [edit]


[0911.3899] Universal Ringdown Amplitudes in Extreme Mass Ratio Inspiral

Authors: Shahar Hadar, Barak Kol

Date: 20 Nov 2009

Abstract: An extreme mass ratio inspiral consists of two parts: adiabatic inspiral and plunge. The plunge trajectory is quite universal (independent of initial conditions). We write an expression for its solution in closed-form and for the emitted universal waveform. In particular we extract an expression for the universal black-hole ringdown amplitudes, which reduces to solving certain ordinary (radial) differential equations in the Schwarzschild background.

abs pdf

Nov 23, 2009

0911.3899 (/preprints)
2009-11-23, 09:06 [edit]


[0911.3889] Understanding possible electromagnetic counterparts to loud gravitational wave events: Binary black hole effects on electromagnetic fields

Authors: Carlos Palenzuela, Luis Lehner, Shin Yoshida

Date: 19 Nov 2009

Abstract: In addition to producing loud gravitational waves (GW), the dynamics of a binary black hole system could induce emission of electromagnetic (EM) radiation by affecting the behavior of plasmas and electromagnetic fields in their vicinity. We here study how the electromagnetic fields are affected by a pair of orbiting black holes through the merger. In particular, we show how the binary's dynamics induce a variability in possible electromagnetically induced emissions as well as an enhancement of electromagnetic fields during the late-merge and merger epochs. These time dependent features will likely leave their imprint in processes generating detectable emissions and can be exploited in the detection of electromagnetic counterparts of gravitational waves.

abs pdf

Nov 23, 2009

0911.3889 (/preprints)
2009-11-23, 09:06 [edit]


[0911.3862] Radiation from low-momentum zoom-whirl orbits

Authors: Roman Gold, Bernd Bruegmann

Date: 19 Nov 2009

Abstract: We study zoom-whirl behaviour of equal mass, non-spinning black hole binaries in full general relativity. The magnitude of the linear momentum of the initial data is fixed to that of a quasi-circular orbit, and its direction is varied. We find a global maximum in radiated energy for a configuration which completes roughly one orbit. The radiated energy in this case exceeds the value of a quasi-circular binary with the same momentum by 15%. The direction parameter only requires minor tuning for the localisation of the maximum. There is non-trivial dependence of the energy radiated on eccentricity (several local maxima and minima). Correlations with orbital dynamics shortly before merger are discussed. While being strongly gauge-dependent, these findings are intuitive from a physical point of view and support basic ideas about the efficiency of gravitational radiation from a binary system.

abs pdf

Nov 23, 2009

0911.3862 (/preprints)
2009-11-23, 09:06 [edit]


[0911.3820] Bayesian coherent analysis of in-spiral gravitational wave signals with a detector network

Authors: John Veitch, Alberto Vecchio

Date: 19 Nov 2009

Abstract: The present operation of the ground-based network of gravitational-wave laser interferometers in "enhanced" configuration brings the search for gravitational waves into a regime where detection is highly plausible. The development of techniques that allow us to discriminate a signal of astrophysical origin from instrumental artefacts in the interferometer data and to extract the full range of information are some of the primary goals of the current work. Here we report the details of a Bayesian approach to the problem of inference for gravitational wave observations using a network of instruments, for the computation of the Bayes factor between two hypotheses and the evaluation of the marginalised posterior density functions of the unknown model parameters. The numerical algorithm to tackle the notoriously difficult problem of the evaluation of large multi-dimensional integrals is based on a technique known as Nested Sampling, which provides an attractive alternative to more traditional Markov-chain Monte Carlo (MCMC) methods. We discuss the details of the implementation of this algorithm and its performance against a Gaussian model of the background noise, considering the specific case of the signal produced by the in-spiral of binary systems of black holes and/or neutron stars, although the method is completely general and can be applied to other classes of sources. We also demonstrate the utility of this approach by introducing a new coherence test to distinguish between the presence of a coherent signal of astrophysical origin in the data of multiple instruments and the presence of incoherent accidental artefacts, and the effects on the estimation of the source parameters as a function of the number of instruments in the network.

abs pdf

Nov 23, 2009

0911.3820 (/preprints)
2009-11-23, 09:06 [edit]


[0911.1274] The importance of precession in modelling the direction of the final spin from a black-hole merger

Authors: Enrico Barausse

Date: 6 Nov 2009

Abstract: The prediction of the spin of the black hole resulting from the merger of a generic black-hole binary system is of great importance to study the cosmological evolution of supermassive black holes. Several attempts have been recently made to model the spin via simple expressions exploiting the results of numerical-relativity simulations. Here I compare the results of all the simulations appeared so far in the literature with various formulas for the final spin magnitude and direction. I show that although all the formulas give reasonable results for the final spin magnitude, only the formula that I recently proposed in (Barausse & Rezzolla, Apj 704 L40) accurately predicts the final spin direction when applied to binaries with separations of hundred or thousands of gravitational radii. This makes my formula particularly suitable for cosmological merger-trees and N-body simulations, which provide the spins and angular momentum of the two black holes when their separation is of thousands of gravitational radii, and happens because my formula takes into account the post-Newtonian precession of the spins in a consistent manner.

abs pdf

Nov 17, 2009

0911.1274 (/preprints)
2009-11-17, 11:46 [edit]


[0911.1806] HST's hunt for intermediate-mass black holes in star clusters

Authors: Julio Chanamé (1), Justice Bruursema (2), Rupali Chandar (3), Jay Anderson (4), Roeland van der Marel (4), Holland Ford (2) ((1) Carnegie DTM, (2) Johns Hopkins University, (3) University of Toledo, (4) Space Telescope Science Institute)

Date: 10 Nov 2009

Abstract: Establishing or ruling out, either through solid mass measurements or upper limits, the presence of intermediate-mass black holes (IMBHs) at the centers of star clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of supermassive black holes. While there are sound theoretical arguments both for and against their presence in today's clusters, observational studies have so far not yielded truly conclusive IMBH detections nor upper limits. We argue that the most promising approach to solving this issue is provided by the combination of measurements of the proper motions of stars at the centers of Galactic globular clusters and dynamical models able to take full advantage of this type of data set. We present a program based on HST observations and recently developed tools for dynamical analysis designed to do just that.

abs pdf

Nov 17, 2009

0911.1806 (/preprints)
2009-11-17, 11:46 [edit]


[0901.0604] Gravitational waves from eccentric intermediate-mass black hole binaries

Authors: Pau Amaro-Seoane, Cole Miller, Marc Freitag

Date: 6 Jan 2009

Abstract: If binary intermediate-mass black holes (IMBHs; with masses between 100 and $10ˆ4 \Msun$) form in dense stellar clusters, their inspiral will be detectable with the planned Laser Interferometer Space Antenna (LISA) out to several Gpc. Here we present a study of the dynamical evolution of such binaries using a combination of direct $N$-body techniques (when the binaries are well separated) and three-body relativistic scattering experiments (when the binaries are tight enough that interactions with stars occur one at a time). We find that for reasonable IMBH masses there is only a mild effect on the structure of the surrounding cluster even though the binary binding energy can exceed the binding energy of the cluster. We demonstrate that, contrary to standard assumptions, the eccentricity in the LISA band can be in {\em some} cases as large as $\sim 0.2 - 0.3$ and that it induces a measurable phase difference from circular binaries in the last year before merger. We also show that, even though energy input from the binary decreases the density of the core and slows down interactions, the total time to coalescence is short enough (typically less than a hundred million years) that such mergers will be unique snapshots of clustered star formation.

abs pdf

Nov 17, 2009

0901.0604 (/preprints)
2009-11-17, 11:45 [edit]


[0911.2431] Evidence for GR rotational frame-dragging in the light from the Sgr A* supermassive black hole

Authors: Bernd Eduard Aschenbach

Date: 12 Nov 2009

Abstract: The analysis of flare start-times confirms the periods found years ago (Aschenbach et al., 2004) in the near-infrared and X-ray light-curves related to the Sgr A* black hole. The assignment of the frequencies found to radial and vertical epicyclic frequencies $\nu\sb{\rm r}$, $\nu\sb{\rm v}$, respectively, as well as to the Kepler orbital frequency $\nu\sb{\rm K}$ reveals resonances of $\nu\sb{\rm v}$ / $\nu\sb{\rm r}$=7:2, and $\nu\sb{\rm K}$ / $\nu\sb{\rm v}$=3:1. The highest observed frequency of 10 mHz is identified as the Kepler frequency corrected by the rotational frame-dragging frequency, as expected from the Lense-Thirring effect. These frequency assignments conclude a black hole mass of M = (4.10-4.34)$\times10\sp{6} M_\odot$ and a spin of a = (0.99473-0.99561).

abs pdf

Nov 17, 2009

0911.2431 (/preprints)
2009-11-17, 11:45 [edit]


[0911.1565] The CBE Hardware Accelerator for Numerical Relativity: A Simple Approach

Authors: Gaurav Khanna

Date: 8 Nov 2009

Abstract: Hardware accelerators (such as the Cell Broadband Engine) have recently received a significant amount of attention from the computational science community because they can provide significant gains in the overall performance of many numerical simulations at a low cost. However, such accelerators usually employ a rather unfamiliar and specialized programming model that often requires advanced knowledge of their hardware design. In this article, we demonstrate an alternate and simpler approach towards managing the main complexities in the programming of the Cell processor, called software caching. We apply this technique to a numerical relativity application: a time-domain, finite-difference Kerr black hole perturbation evolver, and present the performance results. We obtain gains in the overall performance of generic simulations that are close to the theoretical maximum that can be obtained through our parallelization approach.

abs pdf

Nov 17, 2009

0911.1565 (/preprints)
2009-11-17, 11:44 [edit]


[0911.1609] Gravitational Radiation from Hydrodynamic Turbulence in a Differentially Rotating Neutron Star

Authors: A. Melatos, C. Peralta

Date: 9 Nov 2009

Abstract: (Abridged.) The mean-square current quadrupole moment associated with vorticity fluctuations in high-Reynolds-number turbulence in a differentially rotating neutron star is calculated analytically, as are the amplitude and decoherence time of the resulting, stochastic gravitational wave signal. The calculation resolves the subtle question of whether the signal is dominated by the smallest or largest turbulent eddies: for the Kolmogorov-like power spectrum observed in superfluid spherical Couette simulations, the wave strain is controlled by the largest eddies, and the decoherence time approximately equals the maximum eddy turnover time. For a neutron star with spin frequency $\nu_s$ and Rossby number $Ro$, at a distance $d$ from Earth, the root-mean-square wave strain reaches $h_{RMS} \approx 3\times 10ˆ{-24} Roˆ3 (\nu_s / 30 Hz)ˆ3 (d/1 kpc)ˆ{-1}$. A cross-correlation search can detect such a source in principle, because the signal decoheres over the time-scale $\tau_c \approx 10ˆ{-3} Roˆ{-1} (\nu_s / 30 Hz)ˆ{-1} s$, which is adequately sampled by existing long-baseline interferometers. Hence hydrodynamic turbulence imposes a fundamental noise floor on gravitational wave observations of neutron stars, although its polluting effect may be muted by partial decoherence in the hectohertz band, where current continuous-wave searches are concentrated, for the highest frequency (and hence most powerful) sources.

abs pdf

Nov 17, 2009

0911.1609 (/preprints)
2009-11-17, 11:43 [edit]


[0911.1756] Spacetime and orbits of bumpy black holes

Authors: Sarah J. Vigeland, Scott A. Hughes

Date: 9 Nov 2009

Abstract: Our universe contains a great number of extremely compact and massive objects which are generally accepted to be black holes. Precise observations of orbital motion near candidate black holes have the potential to determine if they have the spacetime structure that general relativity demands. As a means of formulating measurements to test the black hole nature of these objects, Collins and Hughes introduced "bumpy black holes": objects that are almost, but not quite, general relativity's black holes. The spacetimes of these objects have multipoles that deviate slightly from the black hole solution, reducing to black holes when the deviation is zero. In this paper, we extend this work in two ways. First, we show how to introduce bumps which are smoother and lead to better behaved orbits than those in the original presentation. Second, we show how to make bumpy Kerr black holes -- objects which reduce to the Kerr solution when the deviation goes to zero. This greatly extends the astrophysical applicability of bumpy black holes. Using Hamilton-Jacobi techniques, we show how a spacetime's bumps are imprinted on orbital frequencies, and thus can be determined by measurements which coherently track a small orbiting body's orbital phase. We find that weak-field orbits of bumpy black holes are modified exactly as expected from a Newtonian analysis of a body with a prescribed multipolar structure, reproducing well-known results from the celestial mechanics literature. The impact of bumps on strong-field orbits is especially strong, suggesting that this framework will allow observations to set robust limits on the extent to which a spacetime's multipoles deviate from the black hole expectation.

abs pdf

Nov 17, 2009

0911.1756 (/preprints)
2009-11-17, 11:43 [edit]


[0911.1816] Lorentz Violation and Gravity

Authors: Quentin G. Bailey

Date: 10 Nov 2009

Abstract: In the last decade, a variety of high-precision experiments have searched for miniscule violations of Lorentz symmetry. These searches are largely motivated by the possibility of uncovering experimental signatures from a fundamental unified theory. Experimental results are reported in the framework called the Standard-Model Extension (SME), which describes general Lorentz violation for each particle species in terms of its coefficients for Lorentz violation. Recently, the role of gravitational experiments in probing the SME has been explored in the literature. In this talk, I will summarize theoretical and experimental aspects of these works. I will also discuss recent lunar laser ranging and atom interferometer experiments, which place stringent constraints on gravity coefficients for Lorentz violation.

abs pdf

Nov 17, 2009

0911.1816 (/preprints)
2009-11-17, 11:42 [edit]


[0911.2139] PPN limit and cosmological gravitational waves as tools to constrain f(R)-gravity

Authors: Mariafelicia De Laurentis, Salvatore Capozziello, Shin'ichi Nojiri, Sergei Odintsov

Date: 11 Nov 2009

Abstract: We discuss the PPN Solar-System constraints and the GW stochastic background considering some recently proposed $f(R)$ gravity models which satisfy both cosmological and stability conditions. Using the definition of PPN-parameters $\gamma$ and $\beta$ in terms of $f(R)$-models and the definition of scalar GWs, we compare and discuss if it is possible to search for parameter ranges of $f(R)$-models working at Solar System and GW stochastic background scale.

abs pdf

Nov 17, 2009

0911.2139 (/preprints)
2009-11-17, 11:41 [edit]


[0906.0993] Fisher Matrix Preloaded -- Fisher4Cast

Authors: Bruce A. Bassett (SAAO, UCT), Yabebal Fantaye (SISSA, SAAO, UCT), Renée Hlozek (Oxford, SAAO, UCT), Jacques Kotze (UCT)

Date: 4 Jun 2009

Abstract: The Fisher Matrix is the backbone of modern cosmological forecasting. We describe the Fisher4Cast software: a general-purpose, easy-to-use, Fisher Matrix framework. It is open source, rigorously designed and tested and includes a Graphical User Interface (GUI) with automated LATEX file creation capability and point-and-click Fisher ellipse generation. Fisher4Cast was designed for ease of extension and, although written in Matlab, is easily portable to open-source alternatives such as Octave and Scilab. Here we use Fisher4Cast to present new 3-D and 4-D visualisations of the forecasting landscape and to investigate the effects of growth and curvature on future cosmological surveys. Early releases have been available at this http URL since May 2008 with 750 downloads in the first year. Version 2.0 is made public with this paper and includes a Quick Start guide and the code used to produce the figures in this paper, in the hope that it will be useful to the cosmology and wider scientific communities.

abs pdf

Nov 17, 2009

0906.0993 (/preprints)
2009-11-17, 10:15 [edit]


[0910.5224] Baryon Acoustic Oscillations

Authors: Bruce A. Bassett (SAAO & UCT), Renée Hlozek (Oxford)

Date: 27 Oct 2009

Abstract: Baryon Acoustic Oscillations (BAO) are frozen relics left over from the pre-decoupling universe. They are the standard rulers of choice for 21st century cosmology, providing distance estimates that are, for the first time, firmly rooted in well-understood, linear physics. This review synthesises current understanding regarding all aspects of BAO cosmology, from the theoretical and statistical to the observational, and includes a map of the future landscape of BAO surveys, both spectroscopic and photometric.

abs pdf

Nov 17, 2009

0910.5224 (/preprints)
2009-11-17, 10:14 [edit]


[0911.2150] Bayesian evidence: can we beat MultiNest using traditional MCMC methods?

Authors: Rutger van Haasteren

Date: 11 Nov 2009

Abstract: Markov Chain Monte Carlo (MCMC) methods have revolutionised Bayesian data analysis over the years by making the direct computation of posterior probability densities feasible on modern workstations. However, the calculation of the prior predictive, the Bayesian evidence, has proved to be notoriously difficult with standard techniques. In this work a method is presented that lets one calculate the Bayesian evidence using nothing but the results from standard MCMC algorithms, like Metropolis-Hastings. This new method is compared to other methods like MultiNest, and greatly outperforms the latter in several cases. One of the toy problems considered in this work is the analysis of mock pulsar timing data, as encountered in pulsar timing array projects. This method is expected to be useful as well in other problems in astrophysics, cosmology and particle physics.

abs pdf

Nov 17, 2009

0911.2150 (/preprints)
2009-11-17, 10:14 [edit]


[0911.2738] LIGO-Virgo searches for gravitational waves from coalescing binaries: a status update

Authors: Anand S. Sengupta, for the LIGO Scientific Collaboration, the Virgo collaboration

Date: 14 Nov 2009

Abstract: Coalescing compact binaries of neutron stars and/or black holes are considered as one of the most promising sources for Earth based gravitational wave detectors. The LIGO-Virgo joint collaboration's Compact Binary Coalescence (CBC) group is searching for gravitational waves emitted by these astrophysical systems by matched filtering the data against theoretically modeled template waveforms. A variety of waveform template families are employed depending on the mass range probed by the search and the stage of the inspiral phase targeted: restricted post-Newtonian for systems having total mass less than $35 \msun$, numerical relativity inspired complete inspiral-merger-ringdown waveforms for more massive systems up to $100\msun$ and ringdown templates for modeling perturbed black holes up to $500\msun$. We give a status update on CBC group's current efforts and upcoming plans in detecting signatures of astrophysical gravitational waves.

abs pdf

Nov 17, 2009

0911.2738 (/preprints)
2009-11-17, 10:13 [edit]


[0911.3020] Mock LISA Data Challenge for the galactic white dwarf binaries

Authors: Arkadiusz Błaut, Stanislav Babak, Andrzej Królak

Date: 16 Nov 2009

Abstract: We present data analysis methods used in detection and the estimation of parameters of gravitational wave signals from the white dwarf binaries in the Mock LISA Data Challenge. Our main focus is on the analysis of Challenge 3.1, where the gravitational wave signals from more than 50 mln. Galactic binaries were added to the simulated Gaussian instrumental noise. Majority of the signals at low frequencies are not resolved individually. The confusion between the signals is strongly reduced at frequencies above 5 mHz. Our basic data analysis procedure is the maximum likelihood detection method. We filter the data through the template bank at the first step of the search, then we refine parameters using the Nelder-Mead algorithm, we remove the strongest signal found and we repeat the procedure. We detect reliably and estimate parameters accurately of more than ten thousand signals from white dwarf binaries.

abs pdf

Nov 17, 2009

0911.3020 (/preprints)
2009-11-17, 10:13 [edit]


[0911.3090] Thermal-noise-limited underground interferometer CLIO

Authors: Kazuhiro Agatsuma, Koji Arai, Masa-Katsu Fujimoto, Seiji Kawamura, Kazuaki Kuroda, Osamu Miyakawa, Shinji Miyoki, Masatake Ohashi, Toshikazu Suzuki, Ryutaro Takahashi, Daisuke Tatsumi, Souichi Telada, Takashi Uchiyama, Kazuhiro Yamamoto, CLIO collaborators

Date: 16 Nov 2009

Abstract: We report on the current status of CLIO (Cryogenic Laser Interferometer Observatory), which is a prototype interferometer for LCGT (Large scale Cryogenic Gravitational-wave Telescope). LCGT is a Japanese next-generation interferometric gravitational wave detector featuring the use of cryogenic mirrors and a quiet underground site. The main purpose of CLIO is to demonstrate a reduction of the mirror thermal noise by cooling the sapphire mirrors. CLIO is located in an underground site of the Kamioka mine, 1000 m deep from the mountain top, to verify its advantages. After a few years of commissioning work, we have achieved a thermal-noise-limited sensitivity at room temperature. One of the main results of noise hunting was the elimination of thermal noise caused by a conductive coil-holder coupled with a pendulum through magnets.

abs pdf

Nov 17, 2009

0911.3090 (/preprints)
2009-11-17, 10:13 [edit]


[0911.1078] Impact of mergers on LISA parameter estimation for nonspinning black hole binaries

Authors: Sean T. McWilliams, James Ira Thorpe, John G. Baker, Bernard J. Kelly

Date: 5 Nov 2009

Abstract: We investigate the precision with which the parameters describing the characteristics and location of nonspinning black hole binaries can be measured with the Laser Interferometer Space Antenna (LISA). By using complete waveforms including the inspiral, merger and ringdown portions of the signals, we find that LISA will have far greater precision than previous estimates for nonspinning mergers that ignored the merger and ringdown. Our analysis covers nonspinning waveforms with moderate mass ratios, q >= 1/10, and total masses 10ˆ5 < M/M_{Sun} < 10ˆ7. We compare the parameter uncertainties using the Fisher matrix formalism, and establish the significance of mass asymmetry and higher-order content to the predicted parameter uncertainties resulting from inclusion of the merger. In real-time observations, the later parts of the signal lead to significant improvements in sky-position precision in the last hours and even the final minutes of observation. For comparable mass systems with total mass M/M_{Sun} = ~10ˆ6, we find that the increased precision resulting from including the merger is comparable to the increase in signal-to-noise ratio. For the most precise systems under investigation, half can be localized to within O(10 arcmin), and 10% can be localized to within O(1 arcmin).

abs pdf

Nov 06, 2009

0911.1078 (/preprints)
2009-11-06, 18:08 [edit]


[0911.1043] Confusion background from compact binaries

Authors: T. Regimbau, Scott A. Hughes

Date: 5 Nov 2009

Abstract: Double neutron stars are one of the most promizing sources for terrestrial gravitational wave interferometers. For actual interferometers and their planned upgrades, the probability of having a signal present in the data is small, but as the sensitivity improves, the detection rate increases and the waveforms may start to overlap, creating a confusion background, ultimately limiting the capabilities of future detectors. The third generation Einstein Telescope, with an horizon of $z > 1$ and very low frequency ‘seismic wall’ may be affected by such confusion noise. At a minimum, careful data analysis will be require to separate signals which will appear confused. This result should be borne in mind when designing highly advanced future instruments.

abs pdf

Nov 06, 2009

0911.1043 (/preprints)
2009-11-06, 18:06 [edit]


[0910.5931] Gravitational waveforms from unequal-mass binaries with arbitrary spins under leading order spin-orbit coupling

Authors: Manuel Tessmer

Date: 30 Oct 2009

Abstract: The paper generalizes the structure of gravitational waves from orbiting spinning binaries under leading order spin-orbit coupling, as given in the work by K\"onigsd\"orffer and Gopakumar [PRD 71, 024039 (2005)] for single-spin and equal-mass binaries, to unequal-mass binaries and arbitrary spin configurations. The orbital motion is taken to be quasi-circular and the fractional mass difference is assumed to be small against one. The emitted gravitational waveforms are given in analytic form.

abs pdf

Nov 05, 2009

0910.5931 (/preprints)
2009-11-05, 10:44 [edit]


[0910.5847] Time, Topology and the Twin Paradox

Authors: J.-P. Luminet

Date: 30 Oct 2009

Abstract: The twin paradox is the best known thought experiment associated with Einstein's theory of relativity. An astronaut who makes a journey into space in a high-speed rocket will return home to find he has aged less than a twin who stayed on Earth. This result appears puzzling, since the situation seems symmetrical, as the homebody twin can be considered to have done the travelling with respect to the traveller. Hence it is called a "paradox". In fact, there is no contradiction and the apparent paradox has a simple resolution in Special Relativity with infinite flat space. In General Relativity (dealing with gravitational fields and curved space-time), or in a compact space such as the hypersphere or a multiply connected finite space, the paradox is more complicated, but its resolution provides new insights about the structure of spacetime and the limitations of the equivalence between inertial reference frames.

abs pdf

Nov 05, 2009

0910.5847 (/preprints)
2009-11-05, 10:44 [edit]


[0910.5818] Light-time computations for the BepiColombo radioscience experiment

Authors: G. Tommei, A. Milani, D. Vokrouhlicky

Date: 30 Oct 2009

Abstract: The radioscience experiment is one of the on board experiment of the Mercury ESA mission BepiColombo that will be launched in 2014. The goals of the experiment are to determine the gravity field of Mercury and its rotation state, to determine the orbit of Mercury, to constrain the possible theories of gravitation (for example by determining the post-Newtonian (PN) parameters), to provide the spacecraft position for geodesy experiments and to contribute to planetary ephemerides improvement. This is possible thanks to a new technology which allows to reach great accuracies in the observables range and range rate; it is well known that a similar level of accuracy requires studying a suitable model taking into account numerous relativistic effects. In this paper we deal with the modelling of the space-time coordinate transformations needed for the light-time computations and the numerical methods adopted to avoid rounding-off errors in such computations.

abs pdf

Nov 05, 2009

0910.5818 (/preprints)
2009-11-05, 10:43 [edit]


[0911.0288] Classifying LISA gravitational wave burst signals using Bayesian evidence

Authors: Farhan Feroz, Jonathan R. Gair, Philip Graff, Michael P Hobson, Anthony Lasenby

Date: 2 Nov 2009

Abstract: We consider the problem of characterisation of burst sources detected with the Laser Interferometer Space Antenna (LISA) using the multi-modal nested sampling algorithm, MultiNest. We use MultiNest as a tool to search for modelled bursts from cosmic string cusps, and compute the Bayesian evidence associated with the cosmic string model. As an alternative burst model, we consider sine-Gaussian burst signals, and show how the evidence ratio can be used to choose between these two alternatives. We present results from an application of MultiNest to the last round of the Mock LISA Data Challenge, in which we were able to successfully detect and characterise all three of the cosmic string burst sources present in the release data set. We also present results of independent trials and show that MultiNest can detect cosmic string signals with signal-to-noise ratio (SNR) as low as ~7 and sine-Gaussian signals with SNR as low as ~8. In both cases, we show that the threshold at which the sources become detectable coincides with the SNR at which the evidence ratio begins to favour the correct model over the alternative.

abs pdf

Nov 05, 2009

0911.0288 (/preprints)
2009-11-05, 10:42 [edit]


[0911.0477] Secular momentum transport by gravitational waves from spinning compact binaries

Authors: Zolt&#xe1;n Keresztes, Bal&#xe1;zs Mik&#xf3;czi, L&#xe1;szl&#xf3; &#xc1;. Gergely, M&#xe1;ty&#xe1;s Vas&#xfa;th

Date: 3 Nov 2009

Abstract: We give a closed system of coupled first order differential equations governing the secular linear momentum loss of a compact binary due to emitted gravitational waves, with the leading order relativistic and spin-orbit perturbations included. In order to close the system, the secular evolution equations of the linear momentum derived from the dissipative dynamics are supplemented with the secular evolutions of the coupled angular variables, as derived from the conservative dynamics.

abs pdf

Nov 05, 2009

0911.0477 (/preprints)
2009-11-05, 10:40 [edit]


[0911.0473] Recovering a spinning inspiralling compact binary waveform immersed in LIGO-like noise with spinning templates

Authors: L&#xe1;szl&#xf3; Ver&#xe9;b, Zolt&#xe1;n Keresztes, P&#xe9;ter Raffai, Szabolcs M&#xe9;sz&#xe1;ros, L&#xe1;szl&#xf3; &#xc1;. Gergely

Date: 3 Nov 2009

Abstract: We investigate the recovery chances of highly spinning waveforms immersed in LIGO S5-like noise by performing a matched filtering with one million randomly chosen spinning waveforms generated with the LAL package. While the masses of the compact binary are reasonably well recovered (slightly overestimated), the same does not hold true for the spins. We show the best fit matches both in the time-domain and the frequency-domain. These encompass some of the spinning characteristics of the signal, but far less, that would be required to identify the astrophysical parameters of the system. An improvement of the matching method is necessary, though may be difficult due to the noisy signal.

abs pdf

Nov 05, 2009

0911.0473 (/preprints)
2009-11-05, 10:40 [edit]


[0911.0525] Test of gravity with polarizations of stochastic gravitational waves around 0.1-1 Hz

Authors: Atsushi Nishizawa, Atsushi Taruya, Seiji Kawamura

Date: 3 Nov 2009

Abstract: In general relativity, a gravitational wave (GW) has two polarization modes, while in modified gravity, the GW is allowed to have additional polarizations. Thus, the observation of the GW polarizations can be utilized for the test of gravity theories. In this letter, we focus on a stochastic GW background (GWB) and classify the polarization modes into tensor, vector, and scalar modes, and then show that the future space-based detectors such as BBO and DECIGO can successfully separate and probe the GWB with the non-Einsteinian polarization modes.

abs pdf

Nov 05, 2009

0911.0525 (/preprints)
2009-11-05, 10:40 [edit]


[0911.0853] Accurate calibration of test mass displacement in the LIGO interferometers

Authors: E. Goetz, R. L. Savage Jr., J. Garofoli, G. Gonzalez, E. Hirose, P. Kalmus, K. Kawabe, J. Kissel, M. Landry, B. O&#x27;Reilly, X. Siemens, A. Stuver, M. Sung

Date: 4 Nov 2009

Abstract: We describe three fundamentally different methods we have applied to calibrate the test mass displacement actuators to search for systematic errors in the calibration of the LIGO gravitational-wave detectors. The actuation frequencies tested range from 90 Hz to 1 kHz and the actuation amplitudes range from 1e-6 m to 1e-18 m. For each of the four test mass actuators measured, the weighted mean coefficient over all frequencies for each technique deviates from the average actuation coefficient for all three techniques by less than 4%. This result indicates that systematic errors in the calibration of the responses of the LIGO detectors to differential length variations are within the stated uncertainties.

abs pdf

Nov 05, 2009

0911.0853 (/preprints)
2009-11-05, 10:39 [edit]


[0910.5222] Dressing the Post-Newtonian two-body problem and Classical Effective Field Theory

Authors: Barak Kol, Michael Smolkin

Date: 28 Oct 2009

Abstract: We apply a dressed perturbation theory to better organize and economize the computation of high orders of the 2-body effective action of an inspiralling Post-Newtonian gravitating binary. We use the effective field theory approach with the non-relativistic field decomposition (NRG fields). For that purpose we develop quite generally the dressing theory of a non-linear classical field theory coupled to point-like sources. We introduce dressed charges and propagators, but unlike the quantum theory there are no dressed bulk vertices. The dressed quantities are found to obey recursive integral equations which succinctly encode parts of the diagrammatic expansion, and are the classical version of the Schwinger-Dyson equations. Actually, the classical equations are somewhat stronger since they involve only finitely many quantities, unlike the quantum theory. Classical diagrams are shown to factorize exactly when they contain non-linear world-line vertices, and we classify all the possible topologies of irreducible diagrams for low loop numbers. We apply the dressing program to our Post-Newtonian case of interest. The dressed charges consist of the dressed energy-momentum tensor after a non-relativistic decomposition, and we compute all dressed charges (in the harmonic gauge) appearing up to 2PN in the 2-body effective action (and more). We determine the irreducible skeleton diagrams up to 3PN and we employ the dressed charges to compute several terms beyond 2PN.

abs pdf

Nov 01, 2009

0910.5222 (/preprints)
2009-11-01, 09:08 [edit]


[0910.5533] Gravitational Self Force in a Schwarzschild Background and the Effective One Body Formalism

Authors: Thibault Damour

Date: 29 Oct 2009

Abstract: We discuss various ways in which the computation of conservative Gravitational Self Force (GSF) effects on a point mass moving in a Schwarzschild background can inform us about the basic building blocks of the Effective One-Body (EOB) Hamiltonian. We display the information which can be extracted from the recently published GSF calculation of the first-GSF-order shift of the orbital frequency of the last stable circular orbit, and we combine this information with the one recently obtained by comparing the EOB formalism to high-accuracy numerical relativity (NR) data on coalescing binary black holes. The information coming from GSF data helps to break the degeneracy (among some EOB parameters) which was left after using comparable-mass NR data to constrain the EOB formalism. We suggest various ways of obtaining more information from GSF computations: either by studying eccentric orbits, or by focussing on a special zero-binding zoom-whirl orbit. We show that logarithmic terms start entering the post-Newtonian expansions of various (EOB and GSF) functions at the fourth post-Newtonian (4PN) level, and we analytically compute the first logarithm entering a certain, gauge-invariant "redshift" GSF function (defined along the sequence of circular orbits).

abs pdf

Nov 01, 2009

0910.5533 (/preprints)
2009-11-01, 09:08 [edit]


[0910.5591] Precise calibration of LIGO test mass actuators using photon radiation pressure

Authors: E. Goetz, P. Kalmus, S. Erickson, R. L. Savage Jr., G. Gonzalez, K. Kawabe, M. Landry, S. Marka, B. O&#x27;Reilly, K. Riles, D. Sigg, P. Willems

Date: 29 Oct 2009

Abstract: Precise calibration of kilometer-scale interferometric gravitational wave detectors is crucial for source localization and waveform reconstruction. A technique that uses the radiation pressure of a power-modulated auxiliary laser to induce calibrated displacements of one of the ~10 kg arm cavity mirrors, a so-called photon calibrator, has been demonstrated previously and has recently been implemented on the LIGO detectors. In this article, we discuss the inherent precision and accuracy of the LIGO photon calibrators and several improvements that have been developed to reduce the estimated voice coil actuator calibration uncertainties to less than 2 percent (1-sigma). These improvements include accounting for rotation-induced apparent length variations caused by interferometer and photon calibrator beam centering offsets, absolute laser power measurement using temperature-controlled InGaAs photodetectors mounted on integrating spheres and calibrated by NIST, minimizing errors induced by localized elastic deformation of the mirror surface by using a two-beam configuration with the photon calibrator beams symmetrically displaced about the center of the optic, and simultaneously actuating the test mass with voice coil actuators and the photon calibrator to minimize fluctuations caused by the changing interferometer response. The photon calibrator is able to operate in the most sensitive interferometer configuration, and is expected to become a primary calibration method for future gravitational wave searches.

abs pdf

Nov 01, 2009

0910.5591 (/preprints)
2009-11-01, 09:07 [edit]


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