1,207 research outputs found
Scalar Polynomial Singularities in Power-Law Spacetimes
Recently, Helliwell and Konkowski (\texttt{gr-qc/0701149}) have examined the
quantum "healing" of some classical singularities in certain power-law
spacetimes. Here I further examine classical properties of these spacetimes and
show that some of them contain naked strong curvature singularities.Comment: 7 pages revtex4 two figures extended discussio
A note on cosmological Levi-Civita spacetimes in higher dimensions
We find a class of solutions to cosmological Einstein equations that
generalizes the four dimensional cylindrically symmetric spacetimes to higher
dimensions. The AdS soliton is a special member of this class with a unique
singularity structure.Comment: 3 pages; version to appear in Phys. Rev.
Cylindrical solutions in braneworld gravity
In this article we investigate exact cylindrically symmetric solutions to the
modified Einstein field equations in the brane world gravity scenarios. It is
shown that for the special choice of the equation of state for the
dark energy and dark pressure, the solutions found could be considered formally
as solutions of the Einstein-Maxwell equations in 4-D general relativity.Comment: 12 pages, RevTex format, typos corrected and references added.
Accepted for publication in PR
Tetrads in Geometrodynamics
A new tetrad is introduced within the framework of geometrodynamics for
non-null electromagnetic fields. This tetrad diagonalizes the electromagnetic
stress-energy tensor and allows for maximum simplification of the expression of
the electromagnetic field. The Einstein-Maxwell equations will also be
simplified
Generating Static Fluid Spheres by Conformal Transformations
We generate an explicit four-fold infinity of physically acceptable exact
perfect fluid solutions of Einstein's equations by way of conformal
transformations of physically unacceptable solutions (one way to view the use
of isotropic coordinates). Special cases include the Schwarzschild interior
solution and the Einstein static universe. The process we consider involves
solving two equations of the Riccati type coupled by a single generating
function rather than a specification of one of the two metric functions.Comment: 4 pages revtex4, two figures, Final form to appear in Phys. Rev.
Generating perfect fluid spheres in general relativity
Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry
describing the interior of a particular idealized general relativistic star --
a static spherically symmetric blob of fluid with position-independent density
-- the general relativity community has continued to devote considerable time
and energy to understanding the general-relativistic static perfect fluid
sphere. Over the last 90 years a tangle of specific perfect fluid spheres has
been discovered, with most of these specific examples seemingly independent
from each other. To bring some order to this collection, in this article we
develop several new transformation theorems that map perfect fluid spheres into
perfect fluid spheres. These transformation theorems sometimes lead to
unexpected connections between previously known perfect fluid spheres,
sometimes lead to new previously unknown perfect fluid spheres, and in general
can be used to develop a systematic way of classifying the set of all perfect
fluid spheres.Comment: 18 pages, 4 tables, 4 figure
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
Timelike and Spacelike Matter Inheritance Vectors in Specific Forms of Energy-Momentum Tensor
This paper is devoted to the investigation of the consequences of timelike
and spacelike matter inheritance vectors in specific forms of energy-momentum
tensor, i.e., for string cosmology (string cloud and string fluid) and perfect
fluid. Necessary and sufficient conditions are developed for a spacetime with
string cosmology and perfect fluid to admit a timelike matter inheritance
vector, parallel to and spacelike matter inheritance vector, parallel to
. We compare the outcome with the conditions of conformal Killing vectors.
This comparison provides us the conditions for the existence of matter
inheritance vector when it is also a conformal Killing vector. Finally, we
discuss these results for the existence of matter inheritance vector in the
special cases of the above mentioned spacetimes.Comment: 27 pages, accepted for publication in Int. J. of Mod. Phys.
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..
A new time-machine model with compact vacuum core
We present a class of curved-spacetime vacuum solutions which develope closed
timelike curves at some particular moment. We then use these vacuum solutions
to construct a time-machine model. The causality violation occurs inside an
empty torus, which constitutes the time-machine core. The matter field
surrounding this empty torus satisfies the weak, dominant, and strong energy
conditions. The model is regular, asymptotically-flat, and
topologically-trivial. Stability remains the main open question.Comment: 7 page
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