275 research outputs found
Stability of Closed Timelike Geodesics
The existence and stability under linear perturbations of closed timelike
geodesics (CTGs) in Bonnor-Ward spacetime is studied in some detail. Regions
where the CTG exist and are linearly stable are exhibited.Comment: 5 pages, REvTex, discussion added. PLA, in pres
Comment on "What does the Letelier-Gal'tsov metric describe?"
We show that the Letelier-Gal'tsov (LG) metric describing multiple crossed
strings in relative motion does solve the Einstein equations, in spite of the
discontinuity uncovered recently by Krasnikov [gr-qc/0502090] provided the
strings are straight and moving with constant velocities.Comment: 3 page
The Letelier-Gal'tsov spacetime revisited
Contrary to a recent claim by Anderson ["The Mathematical Theory of Cosmic
Strings", I.O.P. Publishing, Bristol 2003], we show that the Letelier-Gal'tsov
metric does represent a system of crossed straight infinite cosmic strings
moving with arbitrary constant velocities.Comment: 3 page
Loop Variables for a Class of Conical Spacetimes
Loop variables are used to describe the presence of topological defects in
spacetime. In particular we study the dependence of the holonomy transformation
on angular momentum and torsion for a multi-chiral cone. We also compute the
holonomies for multiple moving crossed cosmic strings and two plane topological
defects-crossed by a cosmic string.Comment: 17 pages, LATE
What does the Letelier-Gal'tsov metric describe?
Recently the structure of the Letelier-Gal'tsov spacetime has become a matter
of some controversy. I show that the metric proposed in \cite{letgal} is
defined only on a dense subset of the whole manifold. In the case when it can
be defined on the remainder by continuity, the resulting spacetime corresponds
to a system of parallel cosmic strings at rest w.r.t. each other.Comment: 4pages, 1 figure. v2 A few words are changed in accordance with the
published versio
Boost-rotation symmetric vacuum spacetimes with spinning sources
Boost-rotation symmetric vacuum spacetimes with spinning sources which
correspond to gravitational field of uniformly accelerated spinning "particles"
are studied. Regularity conditions and asymptotic properties are analyzed. News
functions are derived by transforming the general spinning boost-rotation
symmetric vacuum metric to Bondi-Sachs coordinates.Comment: REVTeX 4, 9 page
Chaos in black holes surrounded by gravitational waves
The occurrence of chaos for test particles moving around Schwarzschild black
holes perturbed by a special class of gravitational waves is studied in the
context of the Melnikov method. The explicit integration of the equations of
motion for the homoclinic orbit is used to reduce the application of this
method to the study of simple graphics.Comment: 15 pages, LaTex
Exact General Relativistic Disks with Magnetic Fields
The well-known ``displace, cut, and reflect'' method used to generate cold
disks from given solutions of Einstein equations is extended to solutions of
Einstein-Maxwell equations. Four exact solutions of the these last equations
are used to construct models of hot disks with surface density, azimuthal
pressure, and azimuthal current. The solutions are closely related to Kerr,
Taub-NUT, Lynden-Bell-Pinault and to a one-soliton solution. We find that the
presence of the magnetic field can change in a nontrivial way the different
properties of the disks. In particular, the pure general relativistic
instability studied by Bicak, Lynden-Bell and Katz [Phys. Rev. D47, 4334, 1993]
can be enhanced or cured by different distributions of currents inside the
disk. These currents, outside the disk, generate a variety of axial symmetric
magnetic fields. As far as we know these are the first models of hot disks
studied in the context of general relativity.Comment: 21 pages, 11 figures, uses package graphics, accepted in PR
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