[1006.4973] Hamiltonian ADM Gravity in Non-Harmonic Gauges with Well Defined Non-Euclidean 3-Spaces: How Much Darkness can be Explained as a Relativistic Inertial Effect?

Authors: Luca Lusanna (INFN)

Date: 25 Jun 2010

Abstract: In special and general relativity the synchronization convention of distant clocks may be simulated with a mathematical definition of global non-inertial frames (the only ones existing in general relativity due to the equivalence principle) with well-defined instantaneous 3-spaces. For asymptotically Minkowskian Einstein space-times this procedure can be used at the Hamiltonian level in the York canonical basis, where it is possible for the first time to disentangle tidal gravitational degrees of freedom from gauge inertial ones. The most important inertial effect connected with clock synchronization is the York time {}ˆ3K(\tau, \sigmaˆr), not existing in Newton gravity. This fact opens the possibility to describe some aspects of {\it darkness} as a relativistic inertial effect in Einstein gravity by means of a Post-Minkowskian reformulation of the Celestial Reference System ICRS.

abs pdf

Jun 30, 2010

1006.4973 (/preprints)
2010-06-30, 00:24 [edit]


[1006.5363] Stochastic resonance with matched filtering

Authors: Li-Fang Li, Jian-Yang Zhu

Date: 28 Jun 2010

Abstract: Along with the development of interferometric gravitational wave detector, we enter into an epoch of gravitational wave astronomy, which will open a brand new window for astrophysics to observe our universe. Almost all of the data analysis methods in gravitational wave detection are based on matched filtering. Gravitational wave detection is a typical example of weak signal detection, and this weak signal is buried in strong instrument noise. So it seems attractable if we can take advantage of stochastic resonance. But unfortunately, almost all of the stochastic resonance theory is based on Fourier transformation and has no relation to matched filtering. In this paper we try to relate stochastic resonance to matched filtering. Our results show that stochastic resonance can indeed be combined with matched filtering for both periodic and non-periodic input signal. This encouraging result will be the first step to apply stochastic resonance to matched filtering in gravitational wave detection. In addition, based on matched filtering, we firstly proposed a novel measurement method for stochastic resonance which is valid for both periodic and non-periodic driven signal.

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Jun 30, 2010

1006.5363 (/preprints)
2010-06-30, 00:22 [edit]


[1006.5394] Galaxy Formation Theory

Authors: Andrew J. Benson (1) ((1) California Institute of Technology)

Date: 28 Jun 2010

Abstract: We review the current theory of how galaxies form within the cosmological framework provided by the cold dark matter paradigm for structure formation. Beginning with the pre-galactic evolution of baryonic material we describe the analytical and numerical understanding of how baryons condense into galaxies, what determines the structure of those galaxies and how internal and external processes (including star formation, merging, active galactic nuclei etc.) determine their gross properties and evolution. Throughout, we highlight successes and failings of current galaxy formation theory. We include a review of computational implementations of galaxy formation theory and assess their ability to provide reliable modeling of this complex phenomenon. We finish with a discussion of several "hot topics" in contemporary galaxy formation theory and assess future directions for this field.

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Jun 30, 2010

1006.5394 (/preprints)
2010-06-30, 00:21 [edit]


[1001.4911] Time Delay Interferometry for LISA with one arm dysfunctional

Authors: S. V. Dhurandhar, K. Rajesh Nayak, J-Y. Vinet

Date: 27 Jan 2010

Abstract: In order to attain the requisite sensitivity for LISA - a joint space mission of the ESA and NASA- the laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. By combining six appropriately time-delayed data streams containing fractional Doppler shifts - a technique called time delay interferometry (TDI) - the laser frequency noise may be adequately suppressed. We consider the general model of LISA where the armlengths vary with time, so that second generation TDI are relevant. However, we must envisage the possibility, that not all the optical links of LISA will be operating at all times, and therefore, we here consider the case of LISA operating with two arms only. As shown earlier in the literature, obtaining even approximate solutions of TDI to the general problem is very difficult. Since here only four optical links are relevant, the algebraic problem simplifies considerably. We are then able to exhibit a large number of solutions (from mathematical point of view an infinite number) and further present an algorithm to generate these solutions.

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Jun 29, 2010

1001.4911 (/preprints)
2010-06-29, 13:52 [edit]


[1006.4644] cuInspiral: prototype gravitational waves detection pipeline fully coded on GPU using CUDA

Authors: Leone B. Bosi

Date: 16 Jun 2010

Abstract: In this paper we report the prototype of the first coalescing binary detection pipeline fully implemented on NVIDIA GPU hardware accelerators. The code has been embedded in a GPU library, called cuInspiral and has been developed under CUDA framework. The library contains for example a PN gravitational wave signal generator, matched filtering/FFT and detection algorithms that have been profiled and compared with the corresponding CPU code with dedicated benchmark in order to provide gain factor respect to the standard CPU implementation. In the paper we present performances and accuracy results about some of the main important elements of the pipeline, demonstrating the feasibility and the chance of obtain an impressive computing gain from these new many-core architectures in the perspective of the second and third generations of gravitational wave detectors.

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Jun 24, 2010

1006.4644 (/preprints)
2010-06-24, 19:21 [edit]


[1006.3768] Genus statistics using the Delaunay tessellation field estimation method: (I) tests with the Millennium Simulation and the SDSS DR7

Authors: Youcai Zhang, Volker Springel, Xiaohu Yang

Date: 18 Jun 2010

Abstract: We study the topology of cosmic large-scale structure through the genus statistics, using galaxy catalogues generated from the Millennium Simulation and observational data from the latest Sloan Digital Sky Survey Data Release (SDSS DR7). We introduce a new method for constructing galaxy density fields and for measuring the genus statistics of its isodensity surfaces. It is based on a Delaunay tessellation field estimation (DTFE) technique that allows the definition of a piece-wise continuous density field and the exact computation of the topology of its polygonal isodensity contours, without introducing any free numerical parameter. Besides this new approach, we also employ the traditional approaches of smoothing the galaxy distribution with a Gaussian of fixed width, or by adaptively smoothing with a kernel that encloses a constant number of neighboring galaxies. Our results show that the Delaunay-based method extracts the largest amount of topological information. Unlike the traditional approach for genus statistics, it is able to discriminate between the different theoretical galaxy catalogues analyzed here, both in real space and in redshift space, even though they are based on the same underlying simulation model. In particular, the DFTE approach detects with high confidence a discrepancy of one of the semi-analytic models studied here compared with the SDSS data, while the other models are found to be consistent.

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Jun 21, 2010

1006.3768 (/preprints)
2010-06-21, 21:14 [edit]


[1006.4139] Next to Leading Order gravitational Spin-Orbit coupling in an Effective Field Theory approach

Authors: Michele Levi

Date: 21 Jun 2010

Abstract: We use an effective field theory (EFT) approach to calculate the next to leading order (NLO) gravitational spin-orbit interaction between two spinning compact objects. The NLO spin-orbit interaction provides the most computationally complex sector of the NLO spin effects, previously derived within the EFT approach. In particular, it requires the inclusion of non-stationary cubic self-gravitational interaction, as well as the implementation of a spin supplementary condition (SSC) at higher orders. The EFT calculation is carried out in terms of the non relativistic gravitational field parametrization, making the calculation more efficient with no need to rely on automated computations, and illustrating the coupling hierarchy of the different gravitational field components to the spin and mass sources. Finally, we show explicitly how to relate the EFT derived spin results to the canonical results obtained with the ADM Hamiltonian formalism. This is done using non-canonical transformations, required due to the implementation of SSC, as well as canonical transformations at the level of the Hamiltonian, with no need to resort to the voluminous equations of motion and cumbersome Dirac brackets.

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Jun 21, 2010

1006.4139 (/preprints)
2010-06-21, 19:45 [edit]


[1006.3903] Motion of small bodies in general relativity: foundations and implementations of the self-force

Authors: Adam Pound

Date: 20 Jun 2010

Abstract: Extreme mass-ratio inspirals, in which solar-mass compact bodies spiral into supermassive black holes, are an important potential source for gravitational wave detectors. Because of the extreme mass-ratio, one can model these systems using perturbation theory. However, in order to relate the motion of the small body to the emitted waveform, one requires a model that is accurate on extremely long timescales. Additionally, in order to avoid intractable divergences, one requires a model that treats the small body as asymptotically small rather than exactly pointlike. Both of these difficulties can be resolved by using techniques of singular perturbation theory. I begin this dissertation with an analysis of singular perturbation theory on manifolds, including the common techniques of matched asymptotic expansions and two-timescale expansions. I then formulate a systematic asymptotic expansion in which the metric perturbation due to the body is expanded while a representative worldline is held fixed, and I contrast it with a regular expansion in which both the metric and the worldline must be expanded. This results in an approximation that is potentially uniformly accurate on long timescales. The equation of motion for the body's fixed worldline is determined by performing a local-in-space expansion in the neighbourhood of the body. Using this local expansion as boundary data, I construct a global solution to the perturbative Einstein equation. To concretely characterize orbits, I next devise a relativistic generalization of the Newtonian method of osculating orbits. Making use of this method and two-timescale expansions, I examine the utility of adiabatic approximations that can forgo an explicit calculation of the force.

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Jun 21, 2010

1006.3903 (/preprints)
2010-06-21, 19:43 [edit]


[0908.3283] DECIGO/BBO as a probe to constrain alternative theories of gravity

Authors: Kent Yagi, Takahiro Tanaka

Date: 23 Aug 2009

Abstract: We calculate how strongly one can constrain the alternative theories of gravity with deci-Hz gravitational wave interferometers such as DECIGO and BBO. Here we discuss Brans-Dicke theory and massive graviton theories as typical examples. We consider the inspiral of compact binaries composed of a neutron star (NS) and an intermediate mass black hole (IMBH) for Brans-Dicke (BD) theory and those composed of a super massive black hole (SMBH) and a black hole (SMBH) for massive graviton theories. Using the restricted 2PN waveforms including spin effects and taking the spin precession into account, we perform the Monte Carlo simulations of $10ˆ4$ binaries to estimate the determination accuracy of binary parameters including the Brans-Dicke parameter $\omega_{\mathrm{BD}}$ and the graviton Compton length $\lambda_g$. Assuming a $(1.4+10)M_{\odot}$ NS/BH binary of SNR=$\sqrt{200}$, the constraint on $\omega_{\mathrm{BD}}$ is obtained as $\omega_{\mathrm{BD}}>1.68\times 10ˆ6$, which is 200 times stronger than the estimated constraint from LISA observation. Furthermore, we find that, due to the expected large merger rate of NS/BH binaries of $O(10ˆ4)$ yr$ˆ{-1}$, a statistical analysis yields $\omega_{\mathrm{BD}}>5.74\times10ˆ7$, which is three orders of magnitude stronger than the current strongest bound obtained from the solar system experiment. For massive graviton theories, assuming a $(10ˆ6+10ˆ5)M_{\odot}$ BH/BH binary at 3Gpc, one can put a constraint $\lambda_g>2.24\times10ˆ{20}$cm, on average. This is three orders of magnitude stronger than the one obtained from the solar system experiment. From these results, it is understood that DECIGO/BBO is a very powerful tool for constraining alternative theories of gravity.

abs pdf

Jun 21, 2010

0908.3283 (/preprints)
2010-06-21, 18:02 [edit]


[1006.3772] Mass Constraints from Eclipse Timing in Double White Dwarf Binaries

Authors: David L Kaplan (KITP)

Date: 18 Jun 2010

Abstract: I demonstrate that an effect similar to the Roemer delay, familiar from timing radio pulsars, should be detectable in the first eclipsing double white dwarf (WD) binary, NLTT 11748. By measuring the difference of the time between the secondary and primary eclipses from one-half period (4.6 s), one can determine the physical size of the orbit and hence constrain the masses of the individual WDs. A measurement with uncertainty <0.1 s — possible with modern large telescopes — will determine the individual masses to +/-0.02 Msun when combined with good-quality (<1 km/s) radial velocity data, although the eccentricity must also be known to high accuracy (+/- 1e-3). Mass constraints improve as Pˆ{-½} (where P is the orbital period), so this works best in wide binaries and should be detectable even for non-degenerate stars, but such constraints require the mass ratio to differ from one and undistorted orbits.

abs pdf

Jun 20, 2010

1006.3772 (/preprints)
2010-06-20, 21:23 [edit]


[1006.3759] Characterizing Spinning Black Hole Binaries in Eccentric Orbits with LISA

Authors: Joey Shapiro Key, Neil J. Cornish

Date: 18 Jun 2010

Abstract: The Laser Interferometer Space Antenna (LISA) is designed to detect gravitational wave signals from astrophysical sources, including those from coalescing binary systems of compact objects such as black holes. Colliding galaxies have central black holes that sink to the center of the merged galaxy and begin to orbit one another and emit gravitational waves. Some galaxy evolution models predict that the binary black hole system will enter the LISA band with significant orbital eccentricity, while other models suggest that the orbits will already have circularized. Using a full seventeen parameter waveform model that includes the effects of orbital eccentricity, spin precession and higher harmonics, we investigate how well the source parameters can be inferred from simulated LISA data. Defining the reference eccentricity as the value one year before merger, we find that for typical LISA sources, it will be possible to measure the eccentricity to an accuracy of parts in a thousand. The accuracy with which the eccentricity can be measured depends only very weakly on the eccentricity, making it possible to distinguish circular orbits from those with very small eccentricities. LISA measurements of the orbital eccentricity can provide strong constraints on theories of galaxy mergers in the early universe.

abs pdf

Jun 20, 2010

1006.3759 (/preprints)
2010-06-20, 21:23 [edit]


[1006.3788] Highly accurate and efficient self-force computations using time-domain methods: Error estimates, validation, and optimization

Authors: Jonathan Thornburg

Date: 18 Jun 2010

Abstract: If a small "particle" of mass $\mu M$ (with $\mu \ll 1$) orbits a Schwarzschild or Kerr black hole of mass $M$, the particle is subject to an $\O(\mu)$ radiation-reaction "self-force". Here I argue that it's valuable to compute this self-force highly accurately (relative error of $\ltsim 10ˆ{-6}$) and efficiently, and I describe techniques for doing this and for obtaining and validating error estimates for the computation. I use an adaptive-mesh-refinement (AMR) time-domain numerical integration of the perturbation equations in the Barack-Ori mode-sum regularization formalism; this is efficient, yet allows easy generalization to arbitrary particle orbits. I focus on the model problem of a scalar particle in a circular geodesic orbit in Schwarzschild spacetime.
The mode-sum formalism gives the self-force as an infinite sum of regularized spherical-harmonic modes $\sum_{\ell=0}ˆ\infty F_{\ell,\reg}$, with $F_{\ell,\reg}$ (and an "internal" error estimate) computed numerically for $\ell \ltsim 30$ and estimated for larger~$\ell$ by fitting an asymptotic "tail" series. Here I validate the internal error estimates for the individual $F_{\ell,\reg}$ using a large set of numerical self-force computations of widely-varying accuracies. I present numerical evidence that the actual numerical errors in $F_{\ell,\reg}$ for different~$\ell$ are at most weakly correlated, so the usual statistical error estimates are valid for computing the self-force. I show that the tail fit is numerically ill-conditioned, but this can be mostly alleviated by renormalizing the basis functions to have similar magnitudes.
Using AMR, fixed mesh refinement, and extended-precision floating-point arithmetic, I obtain the (contravariant) radial component of the self-force for a particle in a circular geodesic orbit of areal radius $r = 10M$ to within $1$~ppm relative error.

abs pdf

Jun 20, 2010

1006.3788 (/preprints)
2010-06-20, 21:23 [edit]


[1006.3563] The Galactic Centre star S2 as a dynamical probe for intermediate-mass black holes

Authors: Alessia Gualandris, Stefan Gillessen, David Merritt

Date: 17 Jun 2010

Abstract: We study the short-term effects of an intermediate mass black hole (IBH) on the orbit of star S2 (S02), the shortest period star known to orbit the supermassive black hole (SBH) in the centre of the Milky Way. Near-infrared imaging and spectroscopic observations allow an accurate determination of the orbit of the star. Given S2's short orbital period and large eccentricity, general relativity (GR) needs to be taken into account, and its effects are potentially measurable with current technology. We show that perturbations due to an IBH in orbit around the SBH can produce a shift in the apoapsis of S2 that is as large or even larger than the GR shift. An IBH will also induce changes in the plane of S2's orbit at a level as large as one degree per period. We apply observational orbital fitting techniques to simulations of the S-cluster in the presence of an IBH and find that an IBH more massive than about 1000 solar masses at the distance of the S-stars will be detectable at the next periapse passage of S2, which will occur in 2018.

abs pdf

Jun 20, 2010

1006.3563 (/preprints)
2010-06-20, 21:23 [edit]


[1006.3326] MYRIAD: A new N-body code for simulations of Star Clusters

Authors: Simos Konstantinidis, Kostas D. Kokkotas

Date: 16 Jun 2010

Abstract: We present a new C++ code for collisional N-body simulations of star clusters. The code uses the Hermite fourth-order scheme with block time steps, for advancing the particles in time, while the forces and neighboring particles are computed using the GRAPE-6 board. Special treatment is used for close encounters, binary and multiple sub-systems that either form dynamically or exist in the initial configuration. The structure of the code is modular and allows the appropriate treatment of more physical phenomena, such as stellar and binary evolution, stellar collisions and evolution of close black-hole binaries. Moreover, it can be easily modified so that the part of the code that uses GRAPE-6, could be replaced by another module that uses other accelerating-hardware like the Graphics Processing Units (GPUs). Appropriate choice of the free parameters give a good accuracy and speed for simulations of star clusters up to and beyond core collapse. Simulations of Plummer models consisting of equal-mass stars reached core collapse at t~17 half-mass relaxation times, which compares very well with existing results, while the cumulative relative error in the energy remained below 0.001. Also, comparisons with published results of other codes for the time of core collapse for different initial conditions, show excellent agreement. Simulations of King models with an initial mass-function, similar to those found in the literature, reached core collapse at t~0.17, which is slightly smaller than the expected result from previous works. Finally, the code accuracy becomes comparable and even better than the accuracy of existing codes, when a number of close binary systems is dynamically created in a simulation. This is due to the high accuracy of the method that is used for close binary and multiple sub-systems.

abs pdf

Jun 17, 2010

1006.3326 (/preprints)
2010-06-17, 21:37 [edit]


[1006.3094] Using the Galileo satellite constellation to test Gravitation

Authors: O. Bertolami, J. P&#xe1;ramos

Date: 15 Jun 2010

Abstract: We consider the feasibility of using the Galileo Navigation Satellite System to constrain possible extensions or modifications to General Relativity, by assessing the impact of the related additions to the Newtonian potential and comparing with the available observables: the relative frequency shift and the delay time of light propagation. We address the impact of deviations from General Relativity based on the parameterized Post-Newtonian parameters, the presence of a Cosmological Constant, of a constant acceleration like the putative Pioneer anomaly, a Yukawa potential term due to massive scalar fields and a power-law potential term, which can arise from ungravity or f(R) theories.

abs pdf

Jun 16, 2010

1006.3094 (/preprints)
2010-06-16, 21:49 [edit]


[1006.3201] Pseudospectral Collocation Methods for the Computation of the Self-Force on a Charged Particle: Generic Orbits around a Schwarzschild Black Hole

Authors: P. Canizares (1), C. F. Sopuerta (1), J. L. Jaramillo (2 and 3) ((1) ICE, CSIC-IEEC, (2) AEI, (3) LUTH)

Date: 16 Jun 2010

Abstract: [abridged] The inspiral of a stellar compact object into a massive black hole is one of the main sources of gravitational waves for the future space-based Laser Interferometer Space Antenna. We expect to be able to detect and analyze many cycles of these slowly inspiraling systems. To that end, the use of very precise theoretical waveform templates in the data analysis is required. To build them we need to have a deep understanding of the gravitational backreaction mechanism responsible for the inspiral. The self-force approach describes the inspiral as the action of a local force that can be obtained from the regularization of the perturbations created by the stellar compact object on the massive black hole geometry. In this paper we extend a new time-domain technique for the computation of the self-force from the circular case to the case of eccentric orbits around a non-rotating black hole. The main idea behind our scheme is to use a multidomain framework in which the small compact object, described as a particle, is located at the interface between two subdomains. Then, the equations at each subdomain are homogeneous wave-type equations, without distributional sources. In this particle-without-particle formulation, the solution of the equations is smooth enough to provide good convergence properties for the numerical computations. This formulation is implemented by using a pseudospectral collocation method for the spatial discretization, combined with a Runge Kutta algorithm for the time evolution. We present results from several simulations of eccentric orbits in the case of a scalar charged particle around a Schwarzschild black hole. In particular, we show the convergence of the method and its ability to resolve the field and its derivatives across the particle location. Finally, we provide numerical values of the self-force for different orbital parameters.

abs pdf

Jun 16, 2010

1006.3201 (/preprints)
2010-06-16, 21:48 [edit]


[0704.0389] Evolution of the Carter constant for inspirals into a black hole: effect of the black hole quadrupole

Authors: Eanna E. Flanagan, Tanja Hinderer

Date: 3 Apr 2007

Abstract: We analyze the effect of gravitational radiation reaction on generic orbits around a body with an axisymmetric mass quadrupole moment Q to linear order in Q, to the leading post-Newtonian order, and to linear order in the mass ratio. This system admits three constants of the motion in absence of radiation reaction: energy, angular momentum, and a third constant analogous to the Carter constant. We compute instantaneous and time-averaged rates of change of these three constants. For a point particle orbiting a black hole, Ryan has computed the leading order evolution of the orbit's Carter constant, which is linear in the spin. Our result, when combined with an interaction quadratic in the spin (the coupling of the black hole's spin to its own radiation reaction field), gives the next to leading order evolution. The effect of the quadrupole, like that of the linear spin term, is to circularize eccentric orbits and to drive the orbital plane towards antialignment with the symmetry axis. In addition we consider a system of two point masses where one body has a single mass multipole or current multipole. To linear order in the mass ratio, to linear order in the multipole, and to the leading post-Newtonian order, we show that there does not exist an analog of the Carter constant for such a system (except for the cases of spin and mass quadrupole). With mild additional assumptions, this result falsifies the conjecture that all vacuum, axisymmetric spacetimes posess a third constant of geodesic motion.

abs pdf

Jun 15, 2010

0704.0389 (/preprints)
2010-06-15, 14:35 [edit]


[1006.2535] First search for gravitational waves from the youngest known neutron star

Authors: LVC

Date: 13 Jun 2010

Abstract: We present a search for periodic gravitational waves from the neutron star in the supernova remnant Cassiopeia A. The search coherently analyzes data in a 12-day interval taken from the fifth science run of the Laser Interferometer Gravitational-Wave Observatory. It searches gravitational wave frequencies from 100 to 300 Hz, and covers a wide range of first and second frequency derivatives appropriate for the age of the remnant and for different spin-down mechanisms. No gravitational wave signal was detected. Within the range of search frequencies, we set 95% confidence upper limits of 0.7--1.2e-24 on the intrinsic gravitational wave strain, 0.4--4e-4 on the equatorial ellipticity of the neutron star, and 0.005--0.14 on the amplitude of r-mode oscillations of the neutron star. These direct upper limits beat indirect limits derived from energy conservation and enter the range of theoretical predictions involving crystalline exotic matter or runaway r-modes. This is the first gravitational wave search to present upper limits on r-modes.

abs pdf

Jun 15, 2010

1006.2535 (/preprints)
2010-06-15, 14:35 [edit]


[0907.2198] A Bayesian approach to the study of white dwarf binaries in LISA data: The application of a reversible jump Markov chain Monte Carlo method

Authors: Alexander Stroeer, John Veitch

Date: 13 Jul 2009

Abstract: The Laser Interferometer Space Antenna (LISA) defines new demands on data analysis efforts in its all-sky gravitational wave survey, recording simultaneously thousands of galactic compact object binary foreground sources and tens to hundreds of background sources like binary black hole mergers and extreme mass ratio inspirals. We approach this problem with an adaptive and fully automatic Reversible Jump Markov Chain Monte Carlo sampler, able to sample from the joint posterior density function (as established by Bayes theorem) for a given mixture of signals "out of the box'', handling the total number of signals as an additional unknown parameter beside the unknown parameters of each individual source and the noise floor. We show in examples from the LISA Mock Data Challenge implementing the full response of LISA in its TDI description that this sampler is able to extract monochromatic Double White Dwarf signals out of colored instrumental noise and additional foreground and background noise successfully in a global fitting approach. We introduce 2 examples with fixed number of signals (MCMC sampling), and 1 example with unknown number of signals (RJ-MCMC), the latter further promoting the idea behind an experimental adaptation of the model indicator proposal densities in the main sampling stage. We note that the experienced runtimes and degeneracies in parameter extraction limit the shown examples to the extraction of a low but realistic number of signals.

abs pdf

Jun 14, 2010

0907.2198 (/preprints)
2010-06-14, 17:40 [edit]


[1006.1994] How to adapt broad-band gravitational-wave searches for r-modes

Authors: Benjamin J. Owen

Date: 10 Jun 2010

Abstract: Up to now there has been no search for gravitational waves from the r-modes of neutron stars in spite of the theoretical interest in the subject. Several oddities of r-modes must be addressed to obtain an observational result: The gravitational radiation field is dominated by the mass current (gravitomagnetic) quadrupole rather than the usual mass quadrupole, and the consequent difference in polarization affects detection statistics and parameter estimation. To astrophysically interpret a detection or upper limit it is necessary to convert the wave amplitude to an r-mode amplitude. Also, it is helpful to know indirect limits on gravitational-wave emission to gauge the interest of various searches. Here I address these issues, thereby providing the ingredients to adapt broad-band searches for continuous gravitational waves to obtain r-mode results. I also show that searches of existing data can already have interesting sensitivities to r-modes.

abs pdf

Jun 10, 2010

1006.1994 (/preprints)
2010-06-10, 22:44 [edit]


[1006.1763] Might black holes reveal their inner secrets?

Authors: Ted Jacobson, Thomas P. Sotiriou

Date: 9 Jun 2010

Abstract: Black holes harbor a spacetime singularity of infinite curvature, where classical spacetime physics breaks down, and current theory cannot predict what will happen. However, the singularity is invisible from the outside because strong gravity traps all signals, even light, behind an event horizon. In this essay we discuss whether it might be possible to destroy the horizon, if a body is tossed into the black hole so as to make it spin faster and/or have more charge than a certain limit. It turns out that one could expose a "naked" singularity if effects of the body's own gravity can be neglected. We suspect however that such neglect is unjustified.

abs pdf

Jun 10, 2010

1006.1763 (/preprints)
2010-06-10, 14:03 [edit]


[1006.1664] Gravitational waves from intermediate-mass black holes in young clusters

Authors: M. Mapelli, C. Huwyler, L. Mayer, Ph. Jetzer, A. Vecchio

Date: 8 Jun 2010

Abstract: Massive young clusters (YCs) are expected to host intermediate-mass black holes (IMBHs) born via runaway collapse. These IMBHs are likely in binaries and can undergo mergers with other compact objects, such as stellar mass black holes (BHs) and neutron stars (NSs). We derive the frequency of such mergers starting from information available in the Local Universe. Mergers of IMBH-NS and IMBH-BH binaries are sources of gravitational waves (GWs), which might allow us to reveal the presence of IMBHs. We thus examine their detectability by current and future GW observatories, both ground- and space-based. In particular, as representative of different classes of instruments we consider Initial and Advanced LIGO, the Einstein gravitational-wave Telescope (ET) and the Laser Interferometer Space Antenna (LISA). We find that IMBH mergers are unlikely to be detected with instruments operating at the current sensitivity (Initial LIGO). LISA detections are disfavored by the mass range of IMBH-NS and IMBH-BH binaries: less than one event per year is expected to be observed by such instrument. Advanced LIGO is expected to observe a few merger events involving IMBH binaries in a 1-year long observation. Advanced LIGO is particularly suited for mergers of relatively light IMBHs (~100 Msun) with stellar mass BHs. The number of mergers detectable with ET is much larger: tens (hundreds) of IMBH-NS (IMBH-BH) mergers might be observed per year, according to the runaway collapse scenario for the formation of IMBHs. We note that our results are affected by large uncertainties, produced by poor observational constraints on many of the physical processes involved in this study, such as the evolution of the YC density with redshift.[abridged]

abs pdf

Jun 10, 2010

1006.1664 (/preprints)
2010-06-10, 14:03 [edit]


[1006.1764] Destroying black holes with test bodies

Authors: Ted Jacobson, Thomas P. Sotiriou

Date: 9 Jun 2010

Abstract: If a black hole can accrete a body whose spin or charge would send the black hole parameters over the extremal limit, then a naked singularity would presumably form, in violation of the cosmic censorship conjecture. We review some previous results on testing cosmic censorship in this way using the test body approximation, focusing mostly on the case of neutral black holes. Under certain conditions a black hole can indeed be over-spun or over-charged in this approximation, hence radiative and self-force effects must be taken into account to further test cosmic censorship.

abs pdf

Jun 10, 2010

1006.1764 (/preprints)
2010-06-10, 14:03 [edit]


[1006.0730] Self consistent model for the evolution of eccentric massive black hole binaries in stellar environments: implications for gravitational wave observations

Authors: A. Sesana

Date: 3 Jun 2010

Abstract: We construct evolutionary tracks for massive black hole binaries (MBHBs) embedded in a surrounding distribution of stars. The dynamics of the binary is evolved by taking into account the erosion of the central stellar cusp bound to the massive black holes, the scattering of unbound stars feeding the binary loss cone, and the emission of gravitational waves (GWs). Stellar dynamics is treated in a hybrid fashion by coupling the results of numerical 3-body scattering experiments of bound and unbound stars to an analytical framework for the evolution of the stellar density distribution and for the efficiency of the binary loss cone refilling. Our main focus is on the behaviour of the binary eccentricity, in the attempt of addressing its importance in the merger process and its possible impact for GW detection with the planned Laser Interferometer Space Antenna ({\it LISA}), and ongoing and forthcoming pulsar timing array (PTA) campaigns. We produce a family of evolutionary tracks extensively sampling the relevant parameters of the system which are the binary mass, mass ratio and initial eccentricity, the slope of the stellar density distribution, its normalization and the efficiency of loss cone refilling. We find that, in general, stellar dynamics causes a dramatic increase of the MBHB eccentricity, especially for initially already mildly eccentric and/or unequal mass binaries. When applied to standard MBHB population models, our results predict eccentricities in the ranges $10ˆ{-3}-0.2$ and $0.03-0.3$ for sources detectable by {\it LISA} and PTA respectively. Such figures may have a significant impact on the signal modelling, on source detection, and on the development of parameter estimation algorithms.

abs pdf

Jun 10, 2010

1006.0730 (/preprints)
2010-06-10, 14:03 [edit]


[1006.1632] Notes on the integration of numerical relativity waveforms

Authors: Christian Reisswig, Denis Pollney

Date: 8 Jun 2010

Abstract: A primary goal of numerical relativity is to provide estimates of the wave strain, $h$, from strong gravitational wave sources, to be used in detector templates. The simulations, however, typically measure waves in terms of gauge resilient quantities, such as the Weyl curvature component, $\psi_4$. Transforming to the strain requires integration of the measured variable twice in time. There are a number of fundamental difficulties which can arise from integrating finite length, discretely sampled and noisy data streams. These issues are related to the post-processing of the data, and thus independent of the characteristics of the original simulation, such as gauge or numerical method used. In particular, secular drifts in integrated waveforms have been observed empirically, but can also be studied with simple analytic models. We demonstrate that regardless of the nature of the original simulation, a degree of uncertainty will always be present in a strain which is calculated by integration. We suggest, however, a simple procedure for integrating numerical waveforms in the frequency domain, which is effective at strongly reducing spurious secular drifts in the resulting strain.

abs pdf

Jun 10, 2010

1006.1632 (/preprints)
2010-06-10, 14:03 [edit]


[1006.0064] The Massive Black Hole and Nuclear Star Cluster in the Center of the Milky Way

Authors: Reinhard Genzel, Frank Eisenhauer, Stefan Gillessen

Date: 1 Jun 2010

Abstract: The Galactic Center is an excellent laboratory for studying phenomena and physical occurring in many other galactic nuclei. The Center of our Milky Way is by far the closest galactic nucleus, and observations with exquisite resolution and sensitivity cover 18 orders of magnitude in energy of electromagnetic radiation. Theoretical simulations have become increasingly more powerful in explaining these measurements. This review summarizes the recent progress in observational and theoretical work on the central parsec, with a strong emphasis on the current empirical evidence for a central massive black hole and on the properties of the surrounding dense star cluster. We present the current evidence, from the analysis of the orbits of more than two dozen stars and from the measurements of the size and motion of the central compact radio source, Sgr A*, that this radio source must be a massive black hole of about 4.4 x 106 M_\odot, beyond any reasonable doubt. We report what is known about the structure and evolution of the dense nuclear star cluster surrounding this black hole, including the astounding fact that stars have been forming in the vicinity of Sgr A* recently, apparently with a top-heavy stellar mass function. We discuss a dense concentration of fainter stars centered in the immediate vicinity of the massive black hole, three of which have orbital peri-bothroi of less than one light day. This 'S-star cluster' appears to consist mainly of young early-type stars, in contrast to the predicted properties of an equilibrium 'stellar cusp' around a black hole. This constitutes a remarkable and presently not fully understood 'paradox of youth'. We also summarize more briefly what is known about the emission properties of the accreting gas onto Sgr A* and how this emission is beginning to delineate the physical properties in the hot accretion zone around the event horizon.

abs pdf

Jun 04, 2010

1006.0064 (/preprints)
2010-06-04, 14:09 [edit]


[1006.0431] Post-Newtonian factorized multipolar waveforms for spinning, non-precessing black-hole binaries

Authors: Yi Pan, Alessandra Buonanno, Ryuichi Fujita, Etienne Racine, Hideyuki Tagoshi

Date: 2 Jun 2010

Abstract: We generalize the factorized resummation of multipolar waveforms introduced by Damour, Iyer and Nagar to spinning black holes. For a nonspinning test-particle spiraling a Kerr black hole in the equatorial plane, we find that factorized multipolar amplitudes which replace the residual relativistic amplitude f_{l m} with its l-th root, \rho_{l m} = f_{l m}ˆ{1/l}, agree quite well with the numerical amplitudes up to the Kerr-spin value q \leq 0.95 for orbital velocities v \leq 0.4. The numerical amplitudes are computed solving the Teukolsky equation with a spectral code. The agreement for prograde orbits and large spin values of the Kerr black hole can be further improved at high velocities by properly factoring out the lower-order post-Newtonian contributions in \rho_{l m}. The resummation procedure results in a better and systematic agreement between numerical and analytical amplitudes (and energy fluxes) than standard Taylor-expanded post-Newtonian approximants. This is particularly true for higher-order modes, such as (2,1), (3,3), (3,2), and (4,4) for which less spin post-Newtonian terms are known. We also extend the factorized resummation of multipolar amplitudes to generic mass-ratio, non-precessing, spinning black holes. Lastly, in our study we employ new, recently computed, higher-order post-Newtonian terms in several subdominant modes, and compute explicit expressions for the half and one-and-half post-Newtonian contributions to the odd-parity (current) and even-parity (odd) multipoles, respectively. Those results can be used to build more accurate templates for ground-based and space-based gravitational-wave detectors.

abs pdf

Jun 04, 2010

1006.0431 (/preprints)
2010-06-04, 14:09 [edit]


[1006.0138] Calibrating spectral estimation for the LISA Technology Package with multichannel synthetic noise generation

Authors: Luigi Ferraioli, Gerhard Heinzel, Martin Hewitson, Mauro Hueller, Anneke Monsky, Miquel Nofrarias, Stefano Vitale

Date: 1 Jun 2010

Abstract: The scientific objectives of the Lisa Technology Package (LTP) experiment, on board of the LISA Pathfinder mission, demand for an accurate calibration and validation of the data analysis tools in advance of the mission launch. The levels of confidence required on the mission outcomes can be reached only with an intense activity on synthetically generated data. A flexible procedure allowing the generation of cross-correlated stationary noise time series was set-up. Multi-channel time series with the desired cross correlation behavior can be generated once a model for a multichannel cross-spectral matrix is provided. The core of the procedure is the synthesis of a noise coloring multichannel filter through a frequency-by-frequency eigendecomposition of the model cross-spectral matrix and a Z-domain fit. The common problem of initial transients in noise time series is solved with a proper initialization of the filter recursive equations. The noise generator performances were tested in a two dimensional case study of the LTP dynamics along the two principal channels of the sensing interferometer.

abs pdf

Jun 04, 2010

1006.0138 (/preprints)
2010-06-04, 14:09 [edit]


[1006.0182] The Lagrange Equilibrium Points L_4 and L_5 in a Black Hole Binary System

Authors: Jeremy D. Schnittman

Date: 1 Jun 2010

Abstract: We calculate the location and stability of the L_4 and L_5 Lagrange equilibrium points in the circular restricted three-body problem as the binary system evolves via gravitational radiation losses. Relative to the purely Newtonian case, we find that the L_4 equilibrium point moves towards the secondary mass and becomes slightly less stable, while the L_5 point moves away from the secondary and gains in stability. We discuss a number of astrophysical applications of these results, in particular as a mechanism for producing electromagnetic counterparts to gravitational-wave signals.

abs pdf

Jun 04, 2010

1006.0182 (/preprints)
2010-06-04, 14:09 [edit]


[1006.0663] High-Precision Numerical Simulations of Rotating Black Holes Accelerated by CUDA

Authors: Rakesh Ginjupalli, Gaurav Khanna

Date: 3 Jun 2010

Abstract: Hardware accelerators (such as Nvidia's CUDA GPUs) have tremendous promise for computational science, because they can deliver large gains in performance at relatively low cost. In this work, we focus on the use of Nvidia's Tesla GPU for high-precision (double, quadruple and octal precision) numerical simulations in the area of black hole physics -- more specifically, solving a partial-differential-equation using finite-differencing. We describe our approach in detail and present the final performance results as compared with a single-core desktop processor and also the Cell BE. We obtain mixed results -- order-of-magnitude gains in overall performance in some cases and negligible gains in others.

abs pdf

Jun 04, 2010

1006.0663 (/preprints)
2010-06-04, 14:09 [edit]


[1005.4655] Search for Gravitational Waves from Compact Binary Coalescence in LIGO and Virgo Data from S5 and VSR1

Authors: the LIGO Scientific Collaboration, the Virgo Collaboration

Date: 25 May 2010

Abstract: We report the results of the first search for gravitational waves from compact binary coalescence using data from the LIGO and Virgo detectors. Five months of data were collected during the concurrent S5 (LIGO) and VSR1 (Virgo) science runs. The search focused on signals from binary mergers with a total mass between 2 and 35 Msun. No gravitational waves are identified. The cumulative 90%-confidence upper limits on the rate of compact binary coalescence are calculated for non-spinning binary neutron stars, black hole-neutron star systems, and binary black holes to be 8.7x10ˆ-3, 2.2x10ˆ-3 and 4.4x10ˆ-4 yrˆ-1 L_10ˆ-1 respectively, where L_10 is 10ˆ10 times the blue solar luminosity. These upper limits are compared with astrophysical expectations.

abs pdf

Jun 01, 2010

1005.4655 (/preprints)
2010-06-01, 12:30 [edit]


[1005.4549] Relic gravitational waves in the light of 7-year Wilkinson Microwave Anisotropy Probe data and improved prospects for the Planck mission

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

Date: 25 May 2010

Abstract: The new release of data from Wilkinson Microwave Anisotropy Probe improves the observational situation with relic gravitational waves. The 7-year results enhance the indications of relic gravitational waves in the existing data and change to the better the prospects of confident detection of relic gravitational waves by the currently operating Planck satellite. We apply to WMAP7 data the same methods of analysis that we used earlier [W. Zhao, D. Baskaran, and L.P. Grishchuk, Phys. Rev. D 80, 083005 (2009)] with WMAP5 data. The maximum likelihood value of the quadrupole ratio $R$, which characterizes the amount of relic gravitational waves, increases up to R=0.264, and the interval separating this value from the point R=0 (the hypothesis of no gravitational waves) increases up to a $2\sigma$ level. Assuming that the WMAP7 maximum likelihood set of parameters is correct, the signal-to-noise ratio $S/N$ for the detection of relic gravitational waves by the Planck experiment increases up to $S/N=4.04$, even under pessimistic assumptions with regard to residual foreground contamination and instrumental noises. We comment on theoretical frameworks that, in the case of success, will be accepted or decisively rejected by the Planck observations.

abs pdf

Jun 01, 2010

1005.4549 (/preprints)
2010-06-01, 12:30 [edit]


[1005.4489] Possible use of self-calibration to reduce systematic uncertainties in determining distance-redshift relation via gravitational radiation from merging binaries

Authors: Tarun Deep Saini, Shiv K. Sethi, Varun Sahni

Date: 25 May 2010

Abstract: By observing mergers of compact objects, future gravity wave experiments would measure the luminosity distance to a large number of sources to a high precision but not their redshifts. Given the directional sensitivity of an experiment, a fraction of such sources (gold plated -- GP) can be identified optically as single objects in the direction of the source. We show that if an approximate distance-redshift relation is known then it is possible to statistically resolve those sources that have multiple galaxies in the beam. We study the feasibility of using gold plated sources to iteratively resolve the unresolved sources, obtain the self-calibrated best possible distance-redshift relation and provide an analytical expression for the accuracy achievable. We derive lower limit on the total number of sources that is needed to achieve this accuracy through self-calibration. We show that this limit depends exponentially on the beam width and give estimates for various experimental parameters representative of future gravitational wave experiments DECIGO and BBO.

abs pdf

Jun 01, 2010

1005.4489 (/preprints)
2010-06-01, 12:29 [edit]


[1005.4735] Gravitational Waves, Sources, and Detectors

Authors: Bernard F Schutz, Franco Ricci

Date: 26 May 2010

Abstract: Notes of lectures for graduate students that were given at Lake Como in 1999, covering the theory of linearized gravitational waves, their sources, and the prospects at the time for detecting gravitational waves. The lectures remain of interest for pedagogical reasons, and in particular because they contain a treatment of current-quadrupole gravitational radiation (in connection with the r-modes of neutron stars) that is not readily available in other sources.

abs pdf

Jun 01, 2010

1005.4735 (/preprints)
2010-06-01, 12:28 [edit]


[1005.5330] Spinning compact binary inspiral II: Conservative angular dynamics

Authors: L&#xe1;szl&#xf3; &#xc1;rp&#xe1;d Gergely

Date: 28 May 2010

Abstract: We establish the evolution equations of the set of independent variables characterizing the 2PN rigorous conservative dynamics of a spinning compact binary, with the inclusion of the leading order spin-orbit, spin-spin and mass quadrupole - mass monopole effects, for generic (noncircular, nonspherical) orbits. More specifically, we give a closed system of first order ordinary differential equations for the orbital elements of the osculating ellipse and for the angles characterizing the spin orientations with respect to the osculating orbit. We also prove that (i) the relative angle of the spins stays constant for equal mass black holes, irrespective of their orientation, and (ii) the special configuration of equal mass black holes with equal, but anti-aligned spins, both laying in the plane of motion (leading to the largest recoil so far) is preserved during the inspiral at 2PN level of accuracy, with leading order spin-orbit, spin-spin and mass quadrupolar contributions included.

abs pdf

Jun 01, 2010

1005.5330 (/preprints)
2010-06-01, 12:27 [edit]


[1005.5228] Gravitational wave asteroseismology with fast rotating neutron stars

Authors: Erich Gaertig, Kostas D. Kokkotas

Date: 28 May 2010

Abstract: We investigate damping and growth times of the f-mode for rapidly rotating stars and a variety of different polytropic equations of state in the Cowling approximation. We discuss the differences in the eigenfunctions of co- and counterrotating modes and compute the damping times of the f-mode for several EoS and all rotation rates up to the Kepler-limit. This is the first study of the damping/growth time of this type of oscillations for fast rotating neutron stars in a general relativistic framework. We use these frequencies and damping/growth times to create robust empirical formulae which can be used for gravitational wave asteroseismology. The estimation of the damping/growth time is based on the quadrupole formula and our results agree very well with Newtonian ones in the appropriate limit.

abs pdf

Jun 01, 2010

1005.5228 (/preprints)
2010-06-01, 12:27 [edit]


[1005.5296] Eccentric Massive Black Hole Binaries in LISA I : The Detection Capabilities of Circular Templates

Authors: Edward K. Porter, Alberto Sesana

Date: 28 May 2010

Abstract: One of the major assumptions in the search for gravitational wave signatures from massive and supermassive black hole binaries with LISA, is that these systems will have circularized before entering the LISA bandwidth. Current astrophysical simulations now suggest that systems could have a non-negligible eccentricity in the LISA band, and an important level of eccentricity in the Pulsar Timing regime. In this work, we use a set of source catalogues from astrophysically motivated models of massive black hole binary formation and assume a one year LISA mission lifetime. Depending on the model in question, the initial eccentricities in the final year of the inspiral can be as high as 0.6 for high mass seeds and 0.8 for low mass seeds. We show that restricted post-Newtonian circular templates are extremely inefficient in recovering eccentric binaries, with median optimal signal to noise ratio recoveries of approximately 10% for all models considered. This coupled with extremely large errors in parameter recovery from individual Markov chain Monte Carlo's demonstrate quite clearly that even to search for binaries with initial eccentricities as low as $10ˆ{-4}$, we will require eccentric templates for LISA data analysis.

abs pdf

Jun 01, 2010

1005.5296 (/preprints)
2010-06-01, 12:27 [edit]


[1005.5163] Sensitivity of Pulsar Timing Arrays to Gravitational Waves

Authors: Brian J. Burt, Andrea N. Lommen, Lee Samuel Finn

Date: 27 May 2010

Abstract: Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on how the available observing time is allocated among the pulsars in the array. Here, we report on a preliminary analysis of observing strategies for the current North American Nanohertz Observatory for Gravitational Waves (NANOGrav) PTA. We also investigate the affects of an additional pulsar on the array sensitivity, with the goal of suggesting where PTA pulsar searches might be best directed. We demonstrate that there exists a slight advantage to finding a new pulsar near where the array is already most sensitive. Further, the study suggests that more observing time should be dedicated to the already low noise pulsars in order to have the greatest positive effect on the PTA sensitivity. We have made a web-based sensitivity mapping tool available at this http URL

abs pdf

Jun 01, 2010

1005.5163 (/preprints)
2010-06-01, 12:26 [edit]


[1005.5560] Statistical constraints on binary black hole inspiral dynamics

Authors: Chad R. Galley, Frank Herrmann, John Silberholz, Manuel Tiglio, Gustavo Guerberoff

Date: 30 May 2010

Abstract: We perform a statistical analysis of the binary black hole problem in the post-Newtonian approximation by systematically sampling and evolving the parameter space of initial configurations for quasi-circular inspirals. Through a principal component analysis of spin and orbital angular momentum variables we systematically look for uncorrelated quantities and find three of them which are highly conserved in a statistical sense, both as functions of time and with respect to variations in initial spin orientations. We also look for and find the variables that account for the largest variations in the problem. We present binary black hole simulations of the full Einstein equations analyzing to what extent these results might carry over to the full theory in the inspiral and merger regimes. Among other applications these results should be useful both in semi-analytical and numerical building of templates of gravitational waves for gravitational wave detectors.

abs pdf

Jun 01, 2010

1005.5560 (/preprints)
2010-06-01, 12:26 [edit]


[1005.5730] Next to leading order spin-orbit effects in the motion of inspiralling compact binaries

Authors: Rafael A. Porto

Date: 31 May 2010

Abstract: Using effective field theory (EFT) techniques we calculate the next-to-leading order (NLO) spin-orbit contributions to the gravitational potential of inspiralling compact binaries. We use the covariant spin supplementarity condition (SSC), and explicitly prove the equivalence with previous results by Faye et al. in arXiv:gr-qc/0605139. We also show that the direct application of the Newton-Wigner SSC at the level of the action leads to the correct dynamics using a canonical (Dirac) algebra. This paper then completes the calculation of the necessary spin dynamics within the EFT formalism that will be used in a separate paper to compute the spin contributions to the energy flux and phase evolution to NLO.

abs pdf

Jun 01, 2010

1005.5730 (/preprints)
2010-06-01, 12:25 [edit]


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