540 research outputs found
Photon rockets moving arbitrarily in any dimension
A family of explicit exact solutions of Einstein's equations in four and
higher dimensions is studied which describes photon rockets accelerating due to
an anisotropic emission of photons. It is possible to prescribe an arbitrary
motion, so that the acceleration of the rocket need not be uniform - both its
magnitude and direction may vary with time. Except at location of the
point-like rocket the spacetimes have no curvature singularities, and
topological defects like cosmic strings are also absent. Any value of a
cosmological constant is allowed. We investigate some particular examples of
motion, namely a straight flight and a circular trajectory, and we derive the
corresponding radiation patterns and the mass loss of the rockets. We also
demonstrate the absence of "gravitational aberration" in such spacetimes. This
interesting member of the higher-dimensional Robinson-Trautman class of pure
radiation spacetimes of algebraic type D generalises the class of Kinnersley's
solutions that has long been known in four-dimensional general relativity.Comment: Text and figures modified (22 pages, 8 figures). To appear in the
International Journal of Modern Physics D, Vol. 20, No..
Purely electromagnetic spacetimes
Electrovacuum solutions devoid of usual mass sources are classified in the
case of one, two and three commuting Killing vectors. Three branches of
solutions exist. Electromagnetically induced mass terms appear in some of them.Comment: 8 page
New Axisymmetric Stationary Solutions of Five-dimensional Vacuum Einstein Equations with Asymptotic Flatness
New axisymmetric stationary solutions of the vacuum Einstein equations in
five-dimensional asymptotically flat spacetimes are obtained by using solitonic
solution-generating techniques. The new solutions are shown to be equivalent to
the four-dimensional multi-solitonic solutions derived from particular class of
four-dimensional Weyl solutions and to include different black rings from those
obtained by Emparan and Reall.Comment: 6 pages, 3 figures;typos corrected, presentations improved,
references added;accepted versio
Rotating Black Holes on Kaluza-Klein Bubbles
Using the solitonic solution generating techniques, we generate a new exact
solution which describes a pair of rotating black holes on a Kaluza-Klein
bubble as a vacuum solution in the five-dimensional Kaluza-Klein theory. We
also investigate the properties of this solution. Two black holes with topology
S^3 are rotating along the same direction and the bubble plays a role in
holding two black holes. In static case, it coincides with the solution found
by Elvang and Horowitz.Comment: 16 pages, 1 figure, minor correctio
Vacuum solutions of five dimensional Einstein equations generated by inverse scattering method
We study stationary and axially symmetric two solitonic solutions of five
dimensional vacuum Einstein equations by using the inverse scattering method
developed by Belinski and Zakharov. In this generation of the solutions, we use
five dimensional Minkowski spacetime as a seed. It is shown that if we restrict
ourselves to the case of one angular momentum component, the generated solution
coincides with a black ring solution with a rotating two sphere which was found
by Mishima and Iguchi recently.Comment: 10 pages, accepted for publication in Physical Review
Isotropy, shear, symmetry and exact solutions for relativistic fluid spheres
The symmetry method is used to derive solutions of Einstein's equations for
fluid spheres using an isotropic metric and a velocity four vector that is
non-comoving. Initially the Lie, classical approach is used to review and
provide a connecting framework for many comoving and so shear free solutions.
This provides the basis for the derivation of the classical point symmetries
for the more general and mathematicaly less tractable description of Einstein's
equations in the non-comoving frame. Although the range of symmetries is
restrictive, existing and new symmetry solutions with non-zero shear are
derived. The range is then extended using the non-classical direct symmetry
approach of Clarkson and Kruskal and so additional new solutions with non-zero
shear are also presented. The kinematics and pressure, energy density, mass
function of these solutions are determined.Comment: To appear in Classical and Quantum Gravit
Relationship Between Solitonic Solutions of Five-Dimensional Einstein Equations
We give the relation between the solutions generated by the inverse
scattering method and the B\"acklund transformation applied to the vacuum
five-dimensional Einstein equations. In particular, we show that the
two-solitonic solutions generated from an arbitrary diagonal seed by the
B\"acklund transformation are contained within those generated from the same
seed by the inverse scattering method.Comment: 17 pages, Some references are added, to be published in Phys.Rev.
Revisiting Cosmic No-Hair Theorem for Inflationary Settings
In this work we revisit Wald's cosmic no-hair theorem in the context of
accelerating Bianchi cosmologies for a generic cosmic fluid with non-vanishing
anisotropic stress tensor and when the fluid energy momentum tensor is of the
form of a cosmological constant term plus a piece which does not respect strong
or dominant energy conditions. Such a fluid is the one appearing in
inflationary models. We show that for such a system anisotropy may grow, in
contrast to the cosmic no-hair conjecture. In particular, for a generic
inflationary model we show that there is an upper bound on the growth of
anisotropy. For slow-roll inflationary models our analysis can be refined
further and the upper bound is found to be of the order of slow-roll
parameters. We examine our general discussions and our extension of Wald's
theorem for three classes of slow-roll inflationary models, generic
multi-scalar field driven models, anisotropic models involving U(1) gauge
fields and the gauge-flation scenario.Comment: 21 pp, 4 .eps figure
No news for Kerr-Schild fields
Algebraically special fields with no gravitational radiation are described.
Kerr-Schild fields, which include as a concrete case the Kinnersley photon
rocket, form an important subclass of them.Comment: 4 pages, Revtex
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