## [gr-qc/0607092] Phenomenology of amplitude-corrected post-Newtonian gravitational waveforms for compact binary inspiral. I. Signal-to-noise ratios

Authors: Chris Van Den Broeck, Anand S. Sengupta

Date: Fri, 21 Jul 2006

Abstract: We study the phenomenological consequences of amplitude-corrected post-Newtonian (PN) gravitational waveforms, as opposed to the more commonly used restricted PN waveforms, for the quasi-circular, adiabatic inspiral of compact binary objects. In the case of initial detectors it has been shown that the use of amplitude-corrected waveforms for detection templates would lead to significantly lower signal-to-noise ratios (SNRs) than those suggested by simulations based exclusively on restricted waveforms. We further elucidate the origin of the effect by an in-depth analytic treatment. The discussion is extended to advanced detectors, where new features emerge. Non-restricted waveforms are linear combinations of harmonics in the orbital phase, and in the frequency domain the $k$th harmonic is cut off at $k f_{LSO}$, with $f_{LSO}$ the orbital frequency at the last stable orbit. As a result, with non-restricted templates it is possible to achieve sizeable signal-to-noise ratios in cases where the dominant harmonic (which is the one at twice the orbital phase) does not enter the detector's bandwidth. This will have important repercussions on the detection of binary inspirals involving intermediate-mass black holes. For sources at a distance of 100 Mpc, taking into account the higher harmonics will double the mass reach of Advanced LIGO, and that of EGO gets tripled. Conservative estimates indicate that the restricted waveforms underestimate detection rates for intermediate mass binary inspirals by at least a factor of twenty.

#### Jul 24, 2006

0607092 (/preprints/gr-qc)
2006-07-24, 16:55 

## [gr-qc/0607065] On the relation between mathematical and numerical relativity

Authors: Lars Andersson (UM and AEI)

Date: Mon, 17 Jul 2006

Abstract: The large scale binary black hole effort in numerical relativity has led to an increasing distinction between numerical and mathematical relativity. This note discusses this situation and gives some examples of succesful interactions between numerical and mathematical methods is general relativity.

#### Jul 18, 2006

0607065 (/preprints/gr-qc)
2006-07-18, 01:29 

## [gr-qc/0607047] Eccentricity content of binary black hole initial data

Authors: Emanuele Berti, Sai Iyer, Clifford M. Will (Washington University, St. Louis)

Date: Tue, 11 Jul 2006

Abstract: Using a post-Newtonian diagnostic tool developed by Mora and Will, we examine numerically generated quasiequilibrium initial data sets that have been used in recently successful numerical evolutions of binary black holes through plunge, merger and ringdown. We show that a small but significant orbital eccentricity is required to match post-Newtonian and quasiequilibrium calculations. If this proves to be a real eccentricity, it could affect the fine details of the subsequent numerical evolutions and the predicted gravitational waveforms.

#### Jul 12, 2006

0607047 (/preprints/gr-qc)
2006-07-12, 01:48 

## [gr-qc/0607045] Graviton Physics

Authors: Barry R. Holstein

Date: Tue, 11 Jul 2006

Abstract: The interactions of gravitons with matter are calculated in parallel with the familiar photon case. It is shown that graviton scattering amplitudes can be factorized into a product of familiar electromagnetic forms, and cross sections for various reactions are straightforwardly evaluated using helicity methods.

#### Jul 12, 2006

0607045 (/preprints/gr-qc)
2006-07-12, 01:47 

## [astro-ph/0607043] Detection regimes of the cosmological gravitational wave background from astrophysical sources

Authors: David Coward, Tania Regimbau

Date: Tue, 4 Jul 2006

Abstract: Key targets for gravitational wave (GW) observatories, such as LIGO and the next generation interferometric detector, Advanced LIGO, include core-collapse of massive stars and the final stage of coalescence of compact stellar remnants. The combined GW signal from such events occurring throughout the Universe will produce an astrophysical GW background (AGB), one that is fundamentally different from the GW background by very early Universe processes. One can classify contributions to the AGB for different classes of sources based on the strength of the GW emissions from the individual sources, their peak emission frequency, emission duration and their event rate density distribution. This article provides an overview of the detectability regimes of the AGB in the context of current and planned gravitational wave observatories. We show that there are two important AGB signal detection regimes, which we define as ‘continuous’ and ‘popcorn noise’. We describe how the ‘popcorn noise’ AGB regime evolves with observation time and we discuss how this feature distinguishes it from the GW background produced from very early Universe processes.

#### Jul 07, 2006

0607043 (/preprints/astro-ph)
2006-07-07, 02:45 

## [gr-qc/0607007] "Kludge" gravitational waveforms for a test-body orbiting a Kerr black hole

Authors: Stanislav Babak, Hua Fang, Jonathan R. Gair, Kostas Glampedakis, Scott A. Hughes

Date: Mon, 3 Jul 2006

Abstract: One of the most exciting potential sources of gravitational waves for low-frequency, space-based gravitational wave (GW) detectors such as the proposed Laser Interferometer Space Antenna (LISA) is the inspiral of compact objects into massive black holes in the centers of galaxies. The detection of waves from such "extreme mass ratio inspiral" systems (EMRIs) and extraction of information from those waves require template waveforms. The systems' extreme mass ratio means that their waveforms can be determined accurately using black hole perturbation theory. Such calculations are computationally very expensive. There is a pressing need for families of approximate waveforms that may be generated cheaply and quickly but which still capture the main features of true waveforms. In this paper, we introduce a family of such "kludge" waveforms and describe ways to generate them. We assess performance of the introduced approximations by comparing "kludge" waveforms to accurate waveforms obtained by solving the Teukolsky equation in the adiabatic limit (neglecting GW backreaction). We find that the kludge waveforms do extremely well at approximating the true gravitational waveform, having overlaps with the Teukolsky waveforms of 95% or higher over most of the parameter space for which comparisons can currently be made. Indeed, we find these kludges to be of such high quality (despite their ease of calculation) that it is possible they may play some role in the final search of LISA data for EMRIs.

#### Jul 04, 2006

0607007 (/preprints/gr-qc)
2006-07-04, 01:20 

## [gr-qc/0606127] Spherical Harmonic Amplitudes From Grid Data

Authors: Mark E. Rupright

Date: Thu, 29 Jun 2006

Abstract: The problem of resolving spherical harmonic components from numerical data defined on a rectangular grid has many applications, particularly for the problem of gravitational radiation extraction. A novel method due to Misner improves on traditional techniques by avoiding the need to cover the sphere with a coordinate system appropriate to the grid geometry. This paper will discuss Misner's method and suggest how it can be improved by exploiting local regression techniques.

#### Jul 04, 2006

0606127 (/preprints/gr-qc)
2006-07-04, 01:18 

## [astro-ph/0606601] Gravity's Relentless Pull: An interactive, multimedia website about black holes for Education and Public Outreach

Authors: Roeland P. van der Marel (STScI), David Schaller (EduWeb), Gijs Verdoes Kleijn (Groningen Univ.)

Date: Fri, 23 Jun 2006

Abstract: We have created a website, called "Black Holes: Gravity's Relentless Pull", which explains the physics and astronomy of black holes for a general audience. The site emphasizes user participation and is rich in animations and astronomical imagery. It won the top prize of the 2005 Pirelli INTERNETional Awards competition for the best communication of science and technology using the internet. This article provides a brief overview of the site. The site starts with an opening animation that introduces the basic concept of a black hole. The user is then invited to embark on a journey from a backyard view of the night sky to a personal encounter with a singularity. This journey proceeds through three modules, which allow the user to: find black holes in the night sky; travel to a black hole in an animated starship; and explore a black hole from up close. There are also five "experiments" that allow the user to: create a black hole; orbit around a black hole; weigh a black hole; drop a clock into a black hole; or fall into a black hole. The modules and experiments offer goal-based scenarios tailored for novices and children. The site also contains an encyclopedia of frequently asked questions and a detailed glossary that are targeted more at experts and adults. The overall result is a website where scientific knowledge, learning theory, and fun converge. Despite its focus on black holes, the site also teaches many other concepts of physics, astronomy and scientific thought. The site aims to instill an appreciation for learning and an interest in science, especially in the younger users. It can be used as an aid in teaching introductory astronomy at the undergraduate level.

#### Jul 04, 2006

0606601 (/preprints/astro-ph)
2006-07-04, 01:17 

## [hep-th/0606226] Quantum effects in gravitational wave signals from cuspy superstrings

Authors: Diego Chialva (SISSA), Thibault Damour (IHES)

Date: Thu, 22 Jun 2006

Abstract: We study the gravitational emission, in Superstring Theory, from fundamental strings exhibiting cusps. The classical computation of the gravitational radiation signal from cuspy strings features strong bursts in the special null directions associated to the cusps. We perform a quantum computation of the gravitational radiation signal from a cuspy string, as measured in a gravitational wave detector using matched filtering and located in the special null direction associated to the cusp. We study the quantum statistics (expectation value and variance) of the measured filtered signal and find that it is very sharply peaked around the classical prediction. Ultimately, this result follows from the fact that the detector is a low-pass filter which is blind to the violent high-frequency quantum fluctuations of both the string worldsheet, and the incoming gravitational field.

#### Jul 04, 2006

0606226 (/preprints/hep-th)
2006-07-04, 01:14 

## [gr-qc/0606104] Numerical evolutions of a black hole-neutron star system in full General Relativity

Authors: Frank Löffler, Luciano Rezzolla, Marcus Ansorg

Date: Fri, 23 Jun 2006

Abstract: We present the first simulations in full General Relativity of the head-on collision between a neutron star and a black hole of comparable mass. These simulations are performed through the solution of the Einstein equations combined with an accurate solution of the relativistic hydrodynamics equations via high-resolution shock-capturing techniques. The initial data is obtained by following the York-Lichnerowicz conformal decomposition with the assumption of time symmetry. Unlike other relativistic studies of such systems, no limitation is set for the mass ratio between the black hole and the neutron star, nor on the position of the black hole, whose apparent horizon is entirely contained within the computational domain. The latter extends over 400 M and is covered with six levels of fixed mesh refinement. Concentrating on a prototypical binary system with mass ratio ~6, we find that although a tidal disruption is evident the neutron star is accreted promptly and entirely into the black hole. While the collision is completed before ~300 M, the evolution is carried over up to ~1700 M, thus providing time for the extraction of the gravitational-wave signal produced and allowing for a first estimate of the radiative efficiency of processes of this type.

#### Jul 04, 2006

0606104 (/preprints/gr-qc)
2006-07-04, 01:14 

## [astro-ph/0606427] Capture Rates of Compact Objects by Supermassive Black Holes

Authors: José Antonio de Freitas Pacheco, Charline Filloux, Tania Regimbau

Date: Sun, 18 Jun 2006

Abstract: Capture rates of compact objects were calculated by using a recent solution of the Fokker-Planck equation in energy-space, including two-body resonant effects. The fraction of compact objects (white dwarfs, neutron stars and stellar black holes) was estimated as a function of the luminosity of the galaxy from a new grid of evolutionary models. Stellar mass densities at the influence radius of central supermassive black holes were derived from brightness profiles obtained by Hubble Space Telescope observations. The present study indicates that the capture rates scale as $\propto M_{bh}ˆ{-1.048}$, consequence of the fact that dwarf galaxies have denser central regions than luminous objects. If the mass distribution of supermassive black holes has a lower cutoff at $\sim 1.4\times 10ˆ6$ M$_{\odot}$ (corresponding to the lowest observed supermassive black hole mass, located in M32), then 9 inspiral events are expected to be seen by LISA (7-8 corresponding to white dwarf captures and 1-2 to neutron star and stellar black hole captures) after one year of operation. However, if the mass distribution extends down to $\sim 2\times 10ˆ5$ M$_{\odot}$, then the total number of expected events increases up to 579 (corresponding to $\sim$ 274 stellar black hole captures, $\sim$ 194 neutron star captures and $\sim$ 111 white dwarf captures).

#### Jul 04, 2006

0606427 (/preprints/astro-ph)
2006-07-04, 01:13 

## [gr-qc/0606093] Light-cone coordinates based at a geodesic world line

Authors: Brent Preston, Eric Poisson

Date: Wed, 21 Jun 2006

Abstract: Continuing work initiated in an earlier publication [Phys. Rev. D 69, 084007 (2004)], we construct a system of light-cone coordinates based at a geodesic world line of an arbitrary curved spacetime. The construction involves (i) an advanced-time or a retarded-time coordinate that labels past or future light cones centered on the world line, (ii) a radial coordinate that is an affine parameter on the null generators of these light cones, and (iii) angular coordinates that are constant on each generator. The spacetime metric is calculated in the light-cone coordinates, and it is expressed as an expansion in powers of the radial coordinate in terms of the irreducible components of the Riemann tensor evaluated on the world line. The formalism is illustrated in two simple applications, the first involving a comoving world line of a spatially-flat cosmology, the other featuring an observer placed on the axis of symmetry of Melvin's magnetic universe.

#### Jul 04, 2006

0606093 (/preprints/gr-qc)
2006-07-04, 01:12