## [gr-qc/0405058] Spin and energy evolution equations for a wide class of extended bodies

Authors: Étienne Racine

Date: Wed, 21 Dec 2005

Abstract: We give a surface integral derivation of the leading-order evolution equations for the spin and energy of a relativistic body interacting with other bodies in the post-Newtonian expansion scheme. The bodies can be arbitrarily shaped and can be strongly self-gravitating. The effects of all mass and current multipoles are taken into account. As part of the computation one of the 2PN potentials parametrizing the metric is obtained. The formulae obtained here for spin and energy evolution coincide with those obtained by Damour, Soffel and Xu for the case of weakly self-gravitating bodies. By combining an Einstein-Infeld-Hoffman-type surface integral approach with multipolar expansions we extend the domain of validity of these evolution equations to a wide class of strongly self-gravitating bodies. This paper completes in a self-contained way a previous work by Racine and Flanagan on translational equations of motion for compact objects.

#### Dec 23, 2005

0405058 (/preprints/gr-qc)
2005-12-23, 13:52 

## [gr-qc/0512125] Projective geometry and special relativity

Authors: David Delphenich

Date: Thu, 22 Dec 2005

Abstract: Some concepts of real and complex projective geometry are applied to the fundamental physical notions that relate to Minkowski space and the Lorentz group. In particular, it is shown that the transition from an infinite speed of propagation for light waves to a finite one entails the replacement of a hyperplane at infinity with a light cone and the replacement of an affine hyperplane - or rest space - with a proper time hyperboloid. The transition from the metric theory of electromagnetism to the pre-metric theory is discussed in the context of complex projective geometry, and ultimately it is proposed that the geometrical issues are more general than electromagnetism, namely, they pertain to the transition from point mechanics to wave mechanics.

#### Dec 23, 2005

0512125 (/preprints/gr-qc)
2005-12-23, 13:51 

## [astro-ph/0510053] Frequency spectrum of gravitational radiation from global hydromagnetic oscillations of a magnetically confined mountain on an accreting neutron star

Authors: D. J. B. Payne, A. Melatos

Date: Mon, 3 Oct 2005

Abstract: Recent time-dependent, ideal-magnetohydrodynamic (ideal-MHD) simulations of polar magnetic burial in accreting neutron stars have demonstrated that stable, magnetically confined mountains form at the magnetic poles, emitting gravitational waves at $f_{*}$ (stellar spin frequency) and $2 f_{*}$. Global MHD oscillations of the mountain, whether natural or stochastically driven, act to modulate the gravitational wave signal, creating broad sidebands (full-width half-maximum $\sim 0.2f_*$) in the frequency spectrum around $f_{*}$ and $2 f_{*}$. The oscillations can enhance the signal-to-noise ratio achieved by a long-baseline interferometer with coherent matched filtering by up to 15 per cent, depending on where $f_*$ lies relative to the noise curve minimum. Coherent, multi-detector searches for continuous waves from nonaxisymmetric pulsars should be tailored accordingly.

#### Dec 13, 2005

0510053 (/preprints/astro-ph)
2005-12-13, 11:37 

## [gr-qc/0512039] Detecting the Cosmic Gravitational Wave Background with the Big Bang Observer

Authors: Vincent Corbin, Neil J. Cornish

Date: Tue, 6 Dec 2005

Abstract: The detection of the Cosmic Microwave Background Radiation (CMB) was one of the most important cosmological discoveries of the last century. With the development of interferometric gravitational wave detectors, we may be in a position to detect the gravitational equivalent of the CMB in this century. The Cosmic Gravitational Background (CGB) is likely to be isotropic and stochastic, making it difficult to distinguish from instrument noise. The contribution from the CGB can be isolated by cross-correlating the signals from two or more independent detectors. Here we extend previous studies that considered the cross-correlation of two Michelson channels by calculating the optimal signal to noise ratio that can be achieved by combining the full set of interferometry variables that are available with a six link triangular interferometer. In contrast to the two channel case, we find that the relative orientation of a pair of coplanar detectors does not affect the signal to noise ratio. We apply our results to the detector design described in the Big Bang Observer (BBO) mission concept study and find that BBO could detect a background with $\Omega_{gw} > 2.2 \times 10ˆ{-17}$.

#### Dec 07, 2005

0512039 (/preprints/gr-qc)
2005-12-07, 10:13 

## [gr-qc/0512028] A Finite Element Computation of the Gravitational Radiation emitted by a Point-like object orbiting a Non-rotating Black Hole

Authors: Carlos F. Sopuerta, Pablo Laguna (Penn State)

Date: Mon, 5 Dec 2005

Abstract: The description of extreme-mass-ratio binary systems in the inspiral phase is a challenging problem in gravitational wave physics with significant relevance for the space interferometer LISA. The main difficulty lies in the evaluation of the effects of the small body's gravitational field on itself. To that end, an accurate computation of the perturbations produced by the small body with respect the background geometry of the large object, a massive black hole, is required. In this paper we present a new computational approach based on Finite Element Methods to solve the master equations describing perturbations of non-rotating black holes due to an orbiting point-like object. The numerical computations are carried out in the time domain by using evolution algorithms for wave-type equations. We show the accuracy of the method by comparing our calculations with previous results in the literature. Finally, we discuss the relevance of this method for achieving accurate descriptions of extreme-mass-ratio binaries.

#### Dec 05, 2005

0512028 (/preprints/gr-qc)
2005-12-05, 22:20 

## [gr-qc/0512014] Tomographic approach to resolving the distribution of LISA Galactic binaries

Authors: Soumya D. Mohanty, Rajesh K. Nayak

Date: Fri, 2 Dec 2005

Abstract: The space based gravitational wave detector LISA is expected to observe a large population of Galactic white dwarf binaries whose collective signal is likely to dominate instrumental noise at observational frequencies in the range 10ˆ{-4} to 10ˆ{-3} Hz. The motion of LISA modulates the signal of each binary in both frequency and amplitude, the exact modulation depending on the source direction and frequency. Starting with the observed response of one LISA interferometer and assuming only doppler modulation due to the orbital motion of LISA, we show how the distribution of the entire binary population in frequency and sky position can be reconstructed using a tomographic approach. The method is linear and the reconstruction of a delta function distribution, corresponding to an isolated binary, yields a point spread function (psf). An arbitrary distribution and its reconstruction are related via smoothing with this psf. Exploratory results are reported demonstrating the recovery of binary sources, in the presence of white Gaussian noise.

#### Dec 04, 2005

0512014 (/preprints/gr-qc)
2005-12-04, 21:40 

## [gr-qc/0512008] Stochastic Background from Coalescences of NS-NS Binaries

Authors: T. Regimbau, J.A de Freitas Pacheco

Date: Thu, 1 Dec 2005

Abstract: In this work, numerical simulations were used to investigate the gravitational stochastic background produced by coalescences occurring up to $z \sim 5$ of double neutron star systems. The cosmic coalescence rate was derived from Monte Carlo methods using the probability distributions for forming a massive binary and to occur a coalescence in a given redshift. A truly continuous background is produced by events located only beyond the critical redshift $z_* = 0.23$. Events occurring in the redshift interval $0.027<z<0.23$ give origin to a "popcorn" noise, while those arising closer than $z = 0.027$ produce a shot noise. The gravitational density parameter $\Omega_{gw}$ for the continuous background reaches a maximum around 670 Hz with an amplitude of $1.1\times 10ˆ{-9}$, while the "popcorn" noise has an amplitude about one order of magnitude higher and the maximum occurs around a frequency of 1.2 kHz. The signal is below the sensitivity of the first generation of detectors but could be detectable by the future generation of ground based interferometers. Correlating two coincident advanced-LIGO detectors or two EGO interferometers, the expected S/N ratio are respectively 0.5 and 10.

#### Dec 01, 2005

0512008 (/preprints/gr-qc)
2005-12-01, 20:50