**Authors**: Naoki Seto

**Date**: 8 Jul 2008

**Abstract**: We propose a non-Gaussianity test for gravitational wave backgrounds by combining data streams of multiple detectors. This simple method allows us to check whether a detected background is "smooth" enough to be consistent with an inflation-type background, or is contaminated by individually undetectable weak burst signals. The proposed test would be quite useful for the Big Bang Observer or DECIGO whose primary target is a background from inflation at 0.1-1Hz where gravitational wave bursts from supernovae of population III stars might become a troublesome foreground.

0807.1151
(/preprints)

2008-07-30, 18:16
**[edit]**

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

**Date**: 25 Jul 2008

**Abstract**: Pulsar glitches are a potential source of gravitational waves for current and future interferometric gravitational wave detectors. Some pulsar glitch events were observed by radio and X-ray telescopes during the fifth LIGO science run. It is expected that glitches from these same pulsars should also be seen in the future. We carried out Monte Carlo simulations to estimate the sensitivity of possible gravitational wave signals associated with a pulsar glitch using a coherent network analysis method. We show the detection efficiency and evaluate the reconstruction accuracy of gravitational waveforms using a matched filter analysis on the estimated gravitational waveforms from the coherent analysis algorithm.

0807.3983
(/preprints)

2008-07-29, 08:28
**[edit]**

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

**Date**: 25 Jul 2008

**Abstract**: Sco X-1, the brightest low mass X-ray binary, is likely to be a source for gravitational wave emission. In one mechanism, emission of a gravitational wave arrests the increase in spin frequency due to the accretion torque in a low mass X-ray binary. Since the gravitational waveform is unknown, a detection method assuming no apriori knowledge of the signal is preferable. In this paper, we propose to search for a gravitational wave from Sco X-1 using a {{\it source tracking}} method based on a coherent network analysis. In the method, we combine data from several interferometric gravitational wave detectors taking into account of the direction to Sco X-1, and reconstruct two polarization waveforms at the location of Sco X-1 in the sky as Sco X-1 is moving. The source tracking method opens up the possibility of searching for a wide variety of signals. We perform Monte Carlo simulations and show results for bursts, modeled, short duration periodic sources using a simple excess power and a matched filter method on the reconstructed signals.

0807.4171
(/preprints)

2008-07-29, 08:28
**[edit]**

**Authors**: Kazuhiro Hayama, Shantanu Desai, Kei Kotake, Soumya D. Mohanty, Malik Rakhmanov, Tiffany Summerscales, Sanichiro Yoshida

**Date**: 28 Jul 2008

**Abstract**: Core-collapse supernovae are promising sources of gravitational waves. The supernova rate in our galaxy is sufficient that a supernova might occur soon and the most probable location is near the Galactic center. The current interferometric gravitational wave detectors such as LIGO and VIRGO can detect these signals from supernovae in our galaxy. Recent simulations of supernova core collapse performed by various groups show that generic features of the waveforms are determined by the rotational nature of the core. Specifically, they predict a negative sign for the second peak in the gravitational wave strain signal if the rotation law of the core dynamics is cylindrical and the differential rotation is strong. The sign of the second peak could be detected by the ground-based gravitational wave detectors. We present a data analysis procedure aiming at the detection of the second peaks using a coherent network analysis and estimated the detection efficiency when a supernova was at the sky location of the Galactic center. The simulations we performed using an idealized network of gravitational waves detectors give encouraging results.

0807.4514
(/preprints)

2008-07-29, 08:27
**[edit]**

**Authors**: John Veitch, Alberto Vecchio

**Date**: 28 Jul 2008

**Abstract**: Bayesian model selection provides a powerful and mathematically transparent framework to tackle hypothesis testing, such as detection tests of gravitational waves emitted during the coalescence of binary systems using ground-based laser interferometers. Although its implementation is computationally intensive, we have developed an efficient probabilistic algorithm based on a technique known as nested sampling that makes Bayesian model selection applicable to follow-up studies of candidate signals produced by on-going searches of inspiralling compact binaries. We discuss the performance of this approach, in terms of "false alarm rate" and "detection probability" of restricted second post-Newtonian inspiral waveforms from non-spinning compact objects in binary systems. The results confirm that this approach is a viable tool for detection tests in current searches for gravitational wave signals.

0807.4483
(/preprints)

2008-07-29, 08:26
**[edit]**

**Authors**: Vitor Cardoso, Oscar J.C. Dias, Pau Figueras

**Date**: 14 Jul 2008

**Abstract**: Some years ago, a new powerful technique, known as the Classical Effective Field Theory, was proposed to describe classical phenomena in gravitational systems. Here we show how this approach can be useful to investigate theoretically important issues, such as gravitational radiation in any spacetime dimension. In particular, we derive for the first time the Einstein-Infeld-Hoffman Lagrangian and we compute Einstein's quadrupole formula for any number of flat spacetime dimensions.

0807.2261
(/preprints)

2008-07-25, 08:59
**[edit]**

**Authors**: Michael Kesden

**Date**: 18 Jul 2008

**Abstract**: Gravitational waves carry away both energy and angular momentum as binary black holes inspiral and merge. The relative efficiency with which they are radiated determines whether the final black hole of mass $M_f$ and spin $S_f$ saturates the Kerr limit ($\chi_f \equiv S_f/M_fˆ2 \leq 1$). Extrapolating from the test-particle limit, we propose expressions for $S_f$ and $M_f$ for mergers with initial spins aligned or anti-aligned with the orbital angular momentum. We predict the the final spin at plunge for equal-mass non-spinning binaries to better than 1%, and that equal-mass maximally spinning aligned mergers lead to nearly maximally spinning final black holes ($\chi_f \simeq 0.9988$). We also find black holes can always be spun up by aligned mergers provided the mass ratio is small enough.

0807.3043
(/preprints)

2008-07-25, 08:59
**[edit]**

**Authors**: Benjamin Koch, Marcus Bleicher, Horst Stoecker

**Date**: 22 Jul 2008

**Abstract**: The upcoming high energy experiments at the LHC are one of the most outstanding efforts for a better understanding of nature. It is associated with great hopes in the physics community. But there is also some fear in the public, that the conjectured production of mini black holes might lead to a dangerous chain reaction. In this paper we summarize the most straightforward proofs that are necessary to rule out such doomsday scenarios.

0807.3349
(/preprints)

2008-07-23, 09:48
**[edit]**

**Authors**: Ryan M. O'Leary, Bence Kocsis, Abraham Loeb

**Date**: 17 Jul 2008

**Abstract**: Stellar mass black holes (BHs) are expected to segregate and form a steep density cusp around supermassive black holes in galactic nuclei. We follow the evolution of a multi-mass system of BHs and stars by numerically integrating the Fokker-Planck energy diffusion equations for a variety of BH mass distributions. We find that the BHs ‘self-segregate’, and that the rarest, most massive BHs dominate the scattering rate closest to the SMBH (< .1 pc). BH--BH binaries form out of gravitational wave emission during BH encounters. We find that the expected rate of BH coalescence events detectable by Advanced LIGO is ~1-1000/yr, depending on the initial mass function of stars in galactic nuclei and the mass of the most massive BHs. The BH binaries that form this way in galactic nuclei have significant eccentricities as they enter the LIGO band (90% with e > 0.9), and are therefore distinguishable from other binaries, which circularize before becoming detectable. We also show that eccentric mergers can be detected to larger distances and greater BH masses than circular mergers, up to ~700 M_sun. Future ground-based gravitational wave observatories will be able to constrain both the mass function of BHs and stars in galactic nuclei.

0807.2638
(/preprints)

2008-07-21, 18:54
**[edit]**

**Authors**: James Healy, Frank Herrmann, Ian Hinder, Deirdre M. Shoemaker, Pablo Laguna, Richard A. Matzner

**Date**: 21 Jul 2008

**Abstract**: Generic inspirals and mergers of binary black holes produce beamed emission of gravitational radiation that can lead to a gravitational recoil or kick of the final black hole. The kick velocity depends on the mass ratio and spins of the binary as well as on the dynamics of the binary configuration. Studies have focused so far on the most astrophysically relevant configuration of quasi-circular inspirals, for which kicks as large as 3,300 km/s have been found. We present the first study of gravitational recoil in hyperbolic encounters. Contrary to quasi-circular configurations, in which the beamed radiation tends to average during the inspiral, radiation from hyperbolic encounters is plunge dominated, resulting in an enhancement of preferential beaming. As a consequence, it is possible to achieve kick velocities as large as 10,000 km/s.

0807.3292
(/preprints)

2008-07-21, 18:54
**[edit]**

**Authors**: Jiri Bicak, Joseph Katz, Donald Lynden-Bell

**Date**: 19 Jul 2008

**Abstract**: Linear and rotational dragging effects of gravitational waves on local inertial frames are studied in purely vacuum spacetimes. First the linear dragging caused by a simple cylindrical pulse is investigated. Surprisingly strong transversal effects of the pulse are exhibited. The angular momentum in cylindrically symmetric spacetimes is then defined and confronted with some results in literature. In the main part, the general procedure is developed for studying weak gravitational waves with translational but not axial symmetry which can carry angular momentum. After a suitable averaging the rotation of local inertial frames due to such rotating waves can be calculated explicitly and illustrated graphically. This is done in detail in the accompanying paper. Finally, the rotational dragging is given for strong cylindrical waves interacting with a rotating cosmic string with a small angular momentum.

0807.3072
(/preprints)

2008-07-21, 18:53
**[edit]**

**Authors**: Rene P. Breton (1), Victoria M. Kaspi (1), Michael Kramer (2), Maura A. McLaughlin (3,4), Maxim Lyutikov (5), Scott M. Ransom (6), Ingrid H. Stairs (7), Robert D. Ferdman (7,8), Fernando Camilo (9), Andrea Possenti (10) ((1) McGill University, (2) Jodrell Bank Centre for Astrophysics, (3) West Virginia University, (4) NRAO Green Bank, (5) Purdue University, (6) NRAO Charlottesville, (7) University of British Columbia, (8) LPCE / CNRS, (9) Columbia University, (10) INAF)

**Date**: 16 Jul 2008

**Abstract**: The double pulsar PSR J0737-3039A/B consists of two neutron stars in a highly relativistic orbit that displays a roughly 30-second eclipse when pulsar A passes behind pulsar B. Describing this eclipse of pulsar A as due to absorption occurring in the magnetosphere of pulsar B, we successfully use a simple geometric model to characterize the observed changing eclipse morphology and to measure the relativistic precession of pulsar B's spin axis around the total orbital angular momentum. This provides a test of general relativity and alternative theories of gravity in the strong-field regime. Our measured relativistic spin precession rate of 4.77 (+0.66,-0.65) degrees per year (68% confidence level) is consistent with that predicted by general relativity within an uncertainty of 13%.

0807.2644
(/preprints)

2008-07-21, 09:13
**[edit]**

**Authors**: Sarah H. Miller, R.A. Matzner

**Date**: 18 Jul 2008

**Abstract**: Thorne and Kidder give expressions which allow for analytical estimates of the "kick", it i.e. the recoil, produced from asymmetrical gravitational radiation during the interaction of black holes, or in fact any gravitating compact bodies. (The Thorne-Kidder formula uses momentum flux calculations based on the linearized General Relativity of gravitational radiation.) We specifically treat kicks arising in the binary interaction of equal mass black holes, when at least one of the black holes has significant spin, a. Such configurations can produce very large kicks in computational simulations. We consider both fly-by and quasicircular orbits. For fly-by orbits we find substantial kicks from those Thorne-Kidder terms which are linear in a. For the quasi-circular case, we consider in addition the nonlinear contribution (O(aˆ2)) to the kicks, and provide a dynamical explanation for such terms. However, in the cases of maximal kick velocities, the dependence on spin is largely linear (reproduced in numerical results).

0807.3028
(/preprints)

2008-07-21, 09:13
**[edit]**

**Authors**: Giovanni Santostasi

**Date**: 16 Jul 2008

**Abstract**: The Laser Interferometer Gravitational Observatory (LIGO) has recently reached the end of its fifth science run (S5), having collected more than a year worth of data. Analysis of the data is still ongoing but a positive detection of gravitational waves, while possible, is not realistically expected for most likely sources. This is particularly true for what concerns gravitational waves from known pulsars. In fact, even under the most optimistic (and not very realistic) assumption that all the pulsar's observed spin-down is due to gravitational waves, the gravitational wave strain at earth from all the known isolated pulsars (with the only notable exception of the Crab pulsar) would not be strong enough to be detectable by existing detectors. By August 2006, LIGO had produced enough data for a coherent integration capable to extract signal from noise that was weaker than the one expected from the Crab pulsar's spin-down limit. No signal was detected, but beating the spin-down limit is a considerable achievement for the LIGO Scientific Collaboration (LSC). It is customary to translate the upper limit on strain from a pulsar into a more astrophysically significant upper limit on ellipticity. Once the spin-down limit has been beaten, it is possible to release the constraint that all the spin-down is due to gravitational wave emission. A more complete model with diverse braking mechanisms can be used to set limits on several astrophysical parameters of the pulsar. This paper shows possible values of such parameters for the Crab pulsar given the current limit on gravitational waves from this neutron star.

0807.2485
(/preprints)

2008-07-16, 18:39
**[edit]**

**Authors**: Sukanta Bose, Achamveedu Gopakumar, Manuel Tessmer

**Date**: 15 Jul 2008

**Abstract**: A new family of restricted post-Newtonian-accurate waveforms, termed TaylorEt approximants, was recently proposed for searching gravitational wave (GW) signals from inspiraling non-spinning compact binaries having arbitrary mass-ratios. We perform detailed fitting factor (FF) studies to probe if the TaylorEt (3.5PN) signals for non-spinning comparable mass compact binaries can be effectually and faithfully searched with TaylorT1, TaylorT4, and TaylorF2 (3.5PN) templates in LIGO, Advanced LIGO, and Virgo interferometers. We observe that a good fraction of the templates, which by choice are from TaylorT1, TaylorT4, and TaylorF2 (3.5PN) families, have FF <~ 0.97 and substantial biases for the estimated total-mass against the fiducial TaylorEt (3.5PN) signals for equal-mass systems. Both these observations can bear on the detectability of a signal. TaylorEt (3.5PN) signals with mass-ratios of a third or a quarter yield high FFs against those same template banks, but at the expense of inviting large systematic errors in the estimated values of their total mass and symmetric mass-ratio. In general, the aforementioned templates are found to be increasingly {\it unfaithful} with respect to a TaylorEt signal as one increases the total mass of the inspiraling system. We also observe that the amount of bias in the estimated mass varies with the (noise power spectral density of the) detector. This can be of some concern for multi-detector searches, which check for consistency in the estimated masses of concurrent triggers in their data. (Abridged)

0807.2400
(/preprints)

2008-07-15, 20:25
**[edit]**

**Authors**: Holger J. Pletsch

**Date**: 9 Jul 2008

**Abstract**: The phase parameters of matched-filtering searches for continuous gravitational-wave signals are sky position, frequency and frequency time-derivatives. The space of these parameters features strong global correlations in the optimal detection statistic. For observation times smaller than one year, the orbital motion of the Earth leads to a family of global-correlation equations which describes the "global maximum structure" of the detection statistic. The solution to each of these equations is a different hypersurface in parameter space. The expected detection statistic is maximal at the intersection of these hypersurfaces. The global maximum structure of the detection statistic from stationary instrumental-noise artifacts is also described by the global-correlation equations. This permits the construction of a veto method which excludes false candidate events.

0807.1324
(/preprints)

2008-07-10, 08:51
**[edit]**

**Authors**: Thibault Damour

**Date**: 8 Jul 2008

**Abstract**: This contribution tries to highlight the importance of Minkowski's ‘Raum und Zeit’ lecture in a ‘negative’ way, where {\it negative} is taken in the photographic sense of reversing lights and shades. Indeed, we focus on the ‘shades’ of Minkowski's text, i.e. what is missing, or misunderstood. In particular, we focus on two issues: (i) why are Poincaré's pioneering contributions to four-dimensional geometry not quoted by Minkowski (while he abundantly quoted them a few months before the Cologne lecture)?, and (ii) did Minkowski fully grasp the physical (and existential) meaning of ‘time’ within spacetime? We think that this ‘negative’ approach (and the contrast between Poincaré's and Minkowski's attitudes towards physics) allows one to better grasp the boldness of the {\it revolutionary} step taken by Minkowski in his Cologne lecture.

0807.1300
(/preprints)

2008-07-08, 18:28
**[edit]**

**Authors**: Alberto Sesana, Alberto Vecchio, Carlo Nicola Colacino

**Date**: 28 Apr 2008

**Abstract**: Massive black hole binary systems, with masses in the range ~10ˆ4-10ˆ10 \msun, are among the primary sources of gravitational waves in the frequency window ~10ˆ-9 Hz - 0.1 Hz. Pulsar Timing Arrays (PTAs) and the Laser Interferometer Space Antenna (LISA) are the observational means by which we will be able to observe gravitational radiation from these systems. We carry out a systematic study of the generation of the stochastic gravitational-wave background from the cosmic population of massive black hole binaries. We consider a wide variety of assembly scenarios and we estimate the range of signal strength in the frequency band accessible to PTAs. We show that, taking into account the uncertainties surrounding the actual key model parameters, the amplitude lies in the interval h_c(f = 10ˆ-8 Hz)~5x10ˆ-16 - 8x10ˆ-15. The most optimistic predictions place the signal level at a factor of ~3 below the current sensitivity of Pulsar Timing Arrays, but within the detection range of the complete Parkes PTA for a wide variety of models, and of the future Square-Kilometer-Array PTA for all the models considered here. We also show that at frequencies >10ˆ-8 Hz the frequency dependency of the generated background follows a power-law significantly steeper than fˆ-2/3, that has been considered so far. Finally we show that LISA observations of individual resolvable massive black hole binaries are complementary and orthogonal to PTA observations of a stochastic background from the whole population in the Universe. In fact, the detection of gravitational radiation in both frequency windows will enable us to fully characterise the cosmic history of massive black holes.

0804.4476
(/preprints)

2008-07-08, 08:36
**[edit]**

**Authors**: David Brizuela, Jose M. Martin-Garcia, Guillermo A. Mena Marugan

**Date**: 6 Jul 2008

**Abstract**: We present the tensor computer algebra package xPert for fast construction and manipulation of the equations of metric perturbation theory, around arbitrary backgrounds. It is based on the combination of explicit combinatorial formulas for the n-th order perturbation of curvature tensors and their gauge changes, and the use of highly efficient techniques of index canonicalization, provided by the underlying tensor system xAct, for Mathematica. We give examples of use and show the efficiency of the system with timings plots: it is possible to handle orders n=4 or n=5 within seconds, or reach n=10 with timings below 1 hour.

0807.0824
(/preprints)

2008-07-08, 08:35
**[edit]**

**Authors**: Ronny Richter, Christian Lubich

**Date**: 7 Jul 2008

**Abstract**: We consider symplectic time integrators in numerical General Relativity and discuss both free and constrained evolution schemes. For free evolution of ADM-like equations we propose the use of the Stoermer-Verlet method, a standard symplectic integrator which here is explicit in the computationally expensive curvature terms. For the constrained evolution we give a formulation of the evolution equations that enforces the momentum constraints in a holonomically constrained Hamiltonian system and turns the Hamilton constraint function from a weak to a strong invariant of the system. This formulation permits the use of the constraint-preserving symplectic RATTLE integrator, a constrained version of the Stoermer-Verlet method.

The behavior of the methods is illustrated on two effectively 1+1-dimensional versions of Einstein's equations, that allow to investigate a perturbed Minkowski problem and the Schwarzschild space-time. We compare symplectic and non-symplectic integrators for free evolution, showing very different numerical behavior for nearly-conserved quantities in the perturbed Minkowski problem. Further we compare free and constrained evolution, demonstrating in our examples that enforcing the momentum constraints can turn an unstable free evolution into a stable constrained evolution. This is demonstrated in the stabilization of a perturbed Minkowski problem with Dirac gauge, and in the suppression of the propagation of boundary instabilities into the interior of the domain in Schwarzschild space-time.

0807.0734
(/preprints)

2008-07-08, 08:35
**[edit]**

**Authors**: Tomas Ledvinka, Gerhard Schaefer, Jiri Bicak

**Date**: 1 Jul 2008

**Abstract**: The Hamiltonian for a system of relativistic bodies interacting by their gravitational field is found in the post-Minkowskian approximation, including all terms linear in the gravitational constant. It is given in a surprisingly simple closed form as a function of canonical variables describing the bodies only. The field is eliminated by solving inhomogeneous wave equations, applying transverse-traceless projections, and using the Routh functional. By including all special relativistic effects our Hamiltonian extends the results described in classical textbooks of theoretical physics. As an application, the scattering of relativistic objects is considered.

0807.0214
(/preprints)

2008-07-04, 07:44
**[edit]**

**Authors**: Ian Hinder, Birjoo Vaishnav, Frank Herrmann, Deirdre Shoemaker, Pablo Laguna

**Date**: 26 Oct 2007

**Abstract**: We present results from numerical relativity simulations of equal mass, non-spinning binary black hole inspirals and mergers with initial eccentricities e <= 0.8 and coordinate separations D >= 12 M of up to 9 orbits (18 gravitational wave cycles). We extract the mass M_f and spin a_f of the final black hole and find, for eccentricities e < 0.4, that a_f/M_f = 0.69 and M_f/M_adm = 0.96 are independent of the initial eccentricity, suggesting that the binary has circularized by the merger time. For e > 0.5, the black holes plunge rather than orbit, and we obtain a maximum spin parameter a_f/M_f = 0.72 around e = 0.5.

0710.5167
(/preprints)

2008-07-04, 07:43
**[edit]**

**Authors**: Jan Harms, Christoph Mahrdt, Markus Otto, Malte Priess

**Date**: 3 Mar 2008

**Abstract**: In this paper, we present a successful implementation of a subtraction-noise projection method into a simple, simulated data analysis pipeline of a gravitational-wave search. We investigate the problem to reveal a weak stochastic background signal which is covered by a strong foreground of compact-binary coalescences. The foreground which is estimated by matched filters, has to be subtracted from the data. Even an optimal analysis of foreground signals will leave subtraction noise due to estimation errors of template parameters which may corrupt the measurement of the background signal. The subtraction noise can be removed by a noise projection. We apply our analysis pipeline to the proposed future-generation space-borne Big Bang Observer (BBO) mission which seeks for a stochastic background of primordial GWs in the frequency range $\sim 0.1-1 $Hz covered by a foreground of black-hole and neutron-star binaries. Our analysis is based on a simulation code which provides a dynamical model of a time-delay interferometer (TDI) network. It generates the data as time series and incorporates the analysis pipeline together with the noise projection. Our results confirm previous ad hoc predictions which say that BBO will be sensitive to backgrounds with fractional energy densities below $\Omega=10ˆ{-16}$

0803.0226
(/preprints)

2008-07-04, 07:42
**[edit]**

**Authors**: Stefanie Komossa, David Merritt

**Date**: 1 Jul 2008

**Abstract**: Supermassive black holes ejected from galaxy nuclei by gravitational wave recoil will carry a retinue of bound stars, even in the absence of an accretion disk. We discuss the observable signatures related to these stars, with an emphasis on electromagnetic flares from stars that are tidally disrupted by the black hole. We calculate disruption rates for the bound, and the unbound, stars. The rates are smaller than, but comparable to, rates for non-recoiling black holes. A key observational consequence is the existence of powerful off-nuclear and intergalactic X-ray flares. We also discuss other observable signatures associated with the bound stars, including episodic X-ray emission from accretion due to stellar mass loss; intergalactic supernovae; and feedback trails.

0807.0223
(/preprints)

2008-07-04, 07:41
**[edit]**

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

*Tantum in modicis, quantum in maximis*