Michele's wiki/blog

Authors: Jeff Crowder, Neil Cornish

Date: Fri, 17 Nov 2006

Abstract: Low frequency gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), will have to contend with large foregrounds produced by millions of compact galactic binaries in our galaxy. While these galactic signals are interesting in their own right, the unresolved component can obscure other sources. The science yield for the LISA mission can be improved if the brighter and more isolated foreground sources can be identified and regressed from the data. Since the signals overlap with one another we are faced with a ‘cocktail party’ problem of picking out individual conversations in a crowded room. Here we present and implement an end-to-end solution to the galactic foreground problem that is able to resolve tens of thousands of sources from across the LISA band. Our algorithm employs a variant of the Markov Chain Monte Carlo (MCMC) method, which we call the Blocked Annealed Metropolis-Hastings (BAM) algorithm. Following a description of the algorithm and its implementation, we give several examples ranging from searches for a single source to searches for hundreds of overlapping sources. Our examples include data sets from the first round of Mock LISA Data Challenges.

abs pdf

Authors: Michael Atiyah, Paul Sutcliffe

Date: Mon, 31 Mar 2003

Abstract: In this article we review some problems in physics, chemistry and mathematics that lead naturally to a class of polyhedra which include the Platonic solids. Examples include the study of electrons on a sphere, cages of carbon atoms, central configurations of gravitating point particles, rare gas microclusters, soliton models of nuclei, magnetic monopole scattering and geometrical problems concerning point particles.

abs pdf

Authors: Christian Corda

Date: Sat, 11 Nov 2006

Abstract: In this paper the "Shibata Nakao and Nakamura" (SNN) gauge for scalar gravitational waves (SGWs)is reanalyzed, showing that in [1] there was an error in the geodesic equations of motion. This error conditioned also the analysis of [2] and [3] where wrong equation of motion taken from [1] were used. In the analysis of the response of interferometers the computation is first made in the low frequencies approximation, then the analysis is applied to all SGWs using a generalization to the SNN gauge of the analysis of [4] where the computation was made in the TT gauge for tensorial waves. At the end of this paper the correct detector pattern of interferometers in the SNN gauge is also computed with a further generalization of the analysis of [4] to the angular dependence of the propagating SGW.

abs pdf

Authors: Carlos F. Sopuerta, Nicolas Yunes, Pablo Laguna

Date: Fri, 3 Nov 2006

Abstract: The formation and growth of supermassive black holes is a key issue to unveil the secrets of galaxy formation. In particular, the gravitational recoil produced in the merger of unequal mass black hole binaries could have a number of astrophysical implications, such as the ejection of black holes from the host galaxy or globular cluster. We present estimates of the recoil velocity that include the effect of small eccentricities. The approach is specially suited for the last stage of the merger, where most of the emission of linear momentum in gravitational waves takes place. Supplementing our estimates with post-Newtonian approximations, we obtain lower and upper bounds that constrain previous recoil velocities estimates as well as a best estimate that agrees with numerical simulations in the quasi-circular case. For eccentricities e <= 0.1, the maximum recoil is found for mass ratios of M_1/M_2 ~ 0.38 with a best estimate of ~ 167 (1 + e) km/s and upper and lower bounds of 79 (1 + e) km/s and 216 (1 + e) km/s respectively.

abs pdf

Authors: Thomas P. Sotiriou, Theocharis A. Apostolatos

Date: Mon, 6 Nov 2006

Abstract: A binary system, composed of a compact object orbiting around a massive central body, will emit gravitational waves which will depend on the central body's spacetime geometry. We expect that the gravitational wave observables will somehow ‘encode’ the information about the spacetime structure. On the other hand, it has been known for some time that the geometry around an axisymmetric body can be described by its (Geroch-Hansen) multipole moments. Therefore one can speculate that using the multipole moments can prove to be a helpful tool for extracting this information. We will try to demonstrate this in this talk, following the procedure described by [F. D. Ryan, Phys. Rev. D {\bf 52} 5707 (1995)] and [T. P. Sotiriou and T. A. Apostolatos, Phys. Rev. D {\bf 71} 044005 (2005)].

abs pdf

Authors: Xavier Siemens, Vuk Mandic, Jolien Creighton

Date: Mon, 30 Oct 2006

Abstract: We consider the stochastic background of gravitational waves produced by a network of cosmic strings and assess their accessibility to current and planned gravitational wave detectors, as well as to the big bang nucleosynthesis (BBN), cosmic microwave background (CMB), and pulsar timing constraints. We find that current data from interferometric gravitational wave detectors, such as LIGO, are sensitive to areas of parameter space of cosmic string models complementary to those accessible to pulsar, BBN, and CMB bounds. Future more sensitive LIGO runs and interferometers such as Advanced LIGO and LISA will be able to explore substantial parts of the parameter space.

abs pdf