1,531 research outputs found
Semiclassical models for uniform-density Cosmic Strings and Relativistic Stars
In this paper we show how quantum corrections, although perturbatively small,
may play an important role in the analysis of the existence of some classical
models. This, in fact, appears to be the case of static, uniform--density
models of the interior metric of cosmic strings and neutron stars. We consider
the fourth order semiclassical equations and first look for perturbative
solutions in the coupling constants and of the quadratic
curvature terms in the effective gravitational Lagrangian. We find that there
is not a consistent solution; neither for strings nor for spherical stars. We
then look for non--perturbative solutions and find an explicit approximate
metric for the case of straight cosmic strings. We finally analyse the
contribution of the non--local terms to the renormalized energy--momentum
tensor and the possibility of this terms to allow for a perturbative solution.
We explicitly build up a particular renormalized energy--momentum tensor to
fulfill that end. These state--dependent corrections are found by simple
considerations of symmetry, conservation law and trace anomaly, and are chosen
to compensate for the local terms. However, they are not only ad hoc, but have
to depend on and , what is not expected to first perturbative
order. We then conclude that non--perturbative solutions are valuable for
describing certain physical situations.Comment: 19 pages, REVTEX, no figure
Algebraic Classification of Numerical Spacetimes and Black-Hole-Binary Remnants
In this paper we develop a technique for determining the algebraic
classification of a numerical spacetime, possibly resulting from a generic
black-hole-binary merger, using the Newman-Penrose Weyl scalars. We demonstrate
these techniques for a test case involving a close binary with arbitrarily
oriented spins and unequal masses. We find that, post merger, the spacetime
quickly approaches Petrov type II, and only approaches type D on much longer
timescales. These techniques allow us to begin to explore the validity of the
"no-hair theorem" for generic merging-black-hole spacetimes.Comment: published versio
Intermediate Mass Ratio Black Hole Binaries: Numerical Relativity meets Perturbation Theory
We study black-hole binaries in the intermediate-mass-ratio regime 0.01 < q <
0.1 with a new technique that makes use of nonlinear numerical trajectories and
efficient perturbative evolutions to compute waveforms at large radii for the
leading and nonleading modes. As a proof-of-concept, we compute waveforms for
q=1/10. We discuss applications of these techniques for LIGO/VIRGO data
analysis and the possibility that our technique can be extended to produce
accurate waveform templates from a modest number of fully-nonlinear numerical
simulations.Comment: 4 pages, 5 figures, revtex
Comparison of Post-Newtonian and Numerical Evolutions of Black-Hole Binaries
In this paper, we compare the waveforms from the post-Newtonian (PN) approach
with the numerical simulations of generic black-hole binaries which have mass
ratio , arbitrarily oriented spins with magnitudes
and , and orbit 9 times from an initial orbital separation of
prior to merger. We observe a reasonably good agreement between
the PN and numerical waveforms, with an overlap of over 98% for the first six
cycles of the mode and over 90% for the and
modes.Comment: 4 pages, 2 figures, prepared for the proceedings of the 18th workshop
on general relativity and gravitation, Hiroshima, Japan, Nov.17 - Nov.21,
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The imposition of Cauchy data to the Teukolsky equation III: The rotating case
We solve the problem of expressing the Weyl scalars that describe
gravitational perturbations of a Kerr black hole in terms of Cauchy data. To do
so we use geometrical identities (like the Gauss-Codazzi relations) as well as
Einstein equations. We are able to explicitly express and as functions only of the extrinsic curvature and the three-metric (and
geometrical objects built out of it) of a generic spacelike slice of the
spacetime. These results provide the link between initial data and to
be evolved by the Teukolsky equation, and can be used to compute the
gravitational radiation generated by two orbiting black holes in the close
limit approximation. They can also be used to extract waveforms from spacetimes
completely generated by numerical methods.Comment: 5 pages, REVTEX, no figure
Perturbative effects of spinning black holes with applications to recoil velocities
Recently, we proposed an enhancement of the Regge-Wheeler-Zerilli formalism
for first-order perturbations about a Schwarzschild background that includes
first-order corrections due to the background black-hole spin. Using this
formalism, we investigate gravitational wave recoil effects from a spinning
black-hole binary system analytically. This allows us to better understand the
origin of the large recoils observed in full numerical simulation of spinning
black hole binaries.Comment: Proceedings of Theory Meets Data Analysis at Comparable and Extreme
Mass Ratios (NRDA/Capra 2010), Perimeter Institute, June 2010 - 12 page
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