206,395 research outputs found
Compact Binary Waveform Center-of-Mass Corrections
We present a detailed study of the center-of-mass (c.m.) motion seen in
simulations produced by the Simulating eXtreme Spacetimes (SXS) collaboration.
We investigate potential physical sources for the large c.m. motion in binary
black hole simulations and find that a significant fraction of the c.m. motion
cannot be explained physically, thus concluding that it is largely a gauge
effect. These large c.m. displacements cause mode mixing in the gravitational
waveform, most easily recognized as amplitude oscillations caused by the
dominant (2,2) modes mixing into subdominant modes. This mixing does not
diminish with increasing distance from the source; it is present even in
asymptotic waveforms, regardless of the method of data extraction. We describe
the current c.m.-correction method used by the SXS collaboration, which is
based on counteracting the motion of the c.m. as measured by the trajectories
of the apparent horizons in the simulations, and investigate potential methods
to improve that correction to the waveform. We also present a complementary
method for computing an optimal c.m. correction or evaluating any other c.m.
transformation based solely on the asymptotic waveform data.Comment: 20 pages, 15 figure
Time-dependent current density functional theory via time-dependent deformation functional theory: A constrained search formulation in the time domain
The logical structure and the basic theorems of time-dependent current
density functional theory (TDCDFT) are analyzed and reconsidered from the point
of view of recently proposed time-dependent deformation functional theory
(TDDefFT). It is shown that the formalism of TDDefFT allows to avoid a
traditional external potential-to-density/current mapping. Instead the theory
is formulated in a form similar to the constrained search procedure in the
ground state DFT. Within this formulation of TDCDFT all basic functionals
appear from the solution of a constrained universal many-body problem in a
comoving reference frame, which is equivalent to finding a conditional extremum
of a certain universal action functional. As a result the physical origin of
the universal functionals entering the theory, as well as their proper causal
structure becomes obvious. In particular, this leaves no room for any doubt
concerning predictive power of the theory.Comment: revtex4, 24 page
From the self-force problem to the Radiation reaction formula
We review a recent theoretical progress in the so-called self-force problem
of a general relativistic two-body system. Although a two-body system in
Newtonian gravity is a very simple problem, some fundamental issues are
involved in relativistic gravity. Besides, because of recent projects for
gravitational wave detection, it comes to be possible to see those phenomena
directly via gravitational waves, and the self-force problem becomes one of
urgent and highly-motivated problems in general relativity. Roughly speaking,
there are two approaches to investigate this problem; the so-called
post-Newtonian approximation, and a black hole perturbation.
In this paper, we review a theoretical progress in the self-force problem
using a black hole perturbation. Although the self-force problem seems to be
just a problem to calculate a self-force, we discuss that the real problem is
to define a gauge invariant concept of a motion in a gauge dependent metric
perturbation.Comment: a special issue for Classical and Quantum Gravity, a review article
of Capra Ranch Meeting
Duality and Four-Dimensional Black Holes
We consider the effects of abelian duality transformations on static,
spherically-symmetric, asymptotically flat string spacetimes in four
dimensions, where the dilaton, axion, metric, and gauge fields are allowed to
be nonzero. Independent of the alpha' expansion, there is a six-parameter
family of such configurations, labelled by the charges characterizing the
asymptotic behaviour of the various fields: ie their mass, dilaton charge,
axion charge, electric charge, magnetic charge, and Taub-NUT parameter. We show
that duality, based on time-translation invariance, maps these solutions
amongst themselves, with the effect of interchanging two pairs of these six
labels, namely: (1) the mass and dilaton charge, and (2) the axion charge and
the Taub-NUT parameter. We consider in detail the special case of the purely
Schwarzschild black hole, for which the mass of the dual configuration vanishes
to leading order in alpha'. Working to next-to-leading order in alpha' for the
bosonic and heterotic strings, we find that duality takes a black hole of mass
M to a (singular) solution having mass - 1/(alpha' M). Finally, we argue that
two solutions which are related by duality based on a noncompact symmetry are
{\it not} always physically equivalent.Comment: plain TeX, 37 pages, no figures. We have made some minor improvements
in presentation and have included some additional reference
Kinematic quantities of finite elastic and plastic deformation
Kinematic quantities for finite elastic and plastic deformations are defined
via an approach that does not rely on auxiliary elements like reference frame
and reference configuration, and that gives account of the inertial-noninertial
aspects explicitly. These features are achieved by working on Galilean
spacetime directly. The quantity expressing elastic deformations is introduced
according to its expected role: to measure how different the current metric is
from the relaxed/stressless metric. Further, the plastic kinematic quantity is
the change rate of the stressless metric. The properties of both are analyzed,
and their relationship to frequently used elastic and plastic kinematic
quantities is discussed. One important result is that no objective elastic or
plastic quantities can be defined from deformation gradient.Comment: v5: minor changes, one section moved to an Appendix, 26 pages, 2
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