282 research outputs found
Kaluza-Klein black hole with negatively curved extra dimensions in string generated gravity models
We obtain a new exact black-hole solution in Einstein-Gauss-Bonnet gravity
with a cosmological constant which bears a specific relation to the
Gauss-Bonnet coupling constant. The spacetime is a product of the usual
4-dimensional manifold with a -dimensional space of constant negative
curvature, i.e., its topology is locally {\ma M}^n \approx {\ma M}^4 \times
{\ma H}^{n-4}. The solution has two parameters and asymptotically approximates
to the field of a charged black hole in anti-de Sitter spacetime. The most
interesting and remarkable feature is that the Gauss-Bonnet term acts like a
Maxwell source for large while at the other end it regularizes the metric
and weakens the central singularity.Comment: 4 pages, 2 figures, final version to appear in Physical Review D as a
rapid communicatio
A spacetime dual to the NUT spacetime
By decomposing the Riemann curvature into electric and magnetic parts, a
duality transformation, which involves interchange of active and passive
electric parts, has recently been proposed. It was shown that the Schwarzschild
solution is dual to the one that describes the Schwarzschild particle with
cloud of string dust or a global monopole. Following the same procedure we
obtain the solution dual to the NUT spacetime.Comment: 10 pages, Latex. Accepted for publication in Classical and Quantum
Gravit
Non-singular black-holes on the brane
We investigate the possibility of obtaining non-singular black-hole solutions
in the brane world model by solving the effective field equations for the
induced metric on the brane. The Reissner-Nordstrom solution on the brane was
obtained by Dadhich etal by imposing the null energy condition on the 3-brane
for a bulk having non zero Weyl curvature. In this work, we relax the condition
of vanishing scalar curvature , however, retaining the null condition. We
have shown that it is possible to obtain class of static non-singular
spherically symmetric brane space-times admitting horizon. We obtain one such
class of solution which is a regular version of the Reissner-Nordstrom solution
in the standard general relativity.Comment: 8 pages, References added, Version to appear in Int. J. Mod. Phys.
Inhomogeneous imperfect fluid spherical models without Big-Bang singularity
So far all known singularity-free cosmological models are cylindrically
symmetric. Here we present a new family of spherically symmetric non-singular
models filled with imperfect fluid and radial heat flow, and satisfying the
weak and strong energy conditions. For large anisotropy in pressure and
heat flux tend to vanish leading to a perfect fluid. There is a free function
of time in the model, which can be suitably chosen for non-singular behaviour
and there exist multiplicity of such choices.Comment: 8 pages, LaTeX versio
Origin of matter out of pure curvature
We propose a mechanism for origin of matter in the universe in the framework
of Einstein-Gauss-Bonnet gravity in higher dimensions. The recently discovered
new static black hole solution by the authors \cite{md2006} with the
Kaluza-Klein split up of spacetime as a product of the usual {\ma M}^4 with a
space of negative constant curvature is indeed a pure gravitational creation of
a black hole which is also endowed with a Maxwell-like {\it gravitational
charge} in four-dimensional vacuum spacetime. Further it could be envisioned as
being formed from anti-de Sitter spacetime by collapse of radially inflowing
charged null dust. It thus establishes the remarkable reciprocity between
matter and gravity - as matter produces gravity (curvature), gravity too
produces matter.Comment: 8 pages, 1 Fig, Received Honorable Mention in 2007 GRF Essay
Competition, Summary of the talk given at Himalayan Relativity Dialogue at
Mirik, April 18-20, 200
A duality relation for fluid spacetime
We consider the electromagnetic resolution of gravitational field. We show
that under the duality transformation, in which active and passive electric
parts of the Riemann curvature are interchanged, a fluid spacetime in comoving
coordinates remains invariant in its character with density and pressure
transforming, while energy flux and anisotropic pressure remaining unaltered.
Further if fluid admits a barotropic equation of state,
where , which will transform to . Clearly the stiff fluid and dust are dual to each-other
while , will go to flat spacetime. However the n and the deSitter ) universes ar e self-dual.Comment: 5 pages, LaTeX version, Accepted in Classical Quantum Gravity as a
Lette
Action based approach to the dynamics of extended bodies in General Relativity
We present, for the first time, an action principle that gives the equations
of motion of an extended body possessing multipole moments in an external
gravitational field, in the weak field limit. From the action, the
experimentally observable quantum phase shifts in the wavefunction of an
extended object due to the coupling of its multipole moments with the
gravitational field are obtained. Also, since the theory may be quantized using
the action, the present approach is useful in the interface between general
relativity and quantum mechanics.Comment: This essay received an ``honorable mention'' in the 2003 Gravity
Research Foundation essay competitio
Singularity: Raychaudhuri Equation once again
I first recount Raychaudhuri's deep involvement with the singularity problem
in general relativity. I then argue that precisely the same situation has
arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered
his celebrated equation. We thus need a new analogue of the Raychaudhuri
equation in quantum gravity.Comment: 11 pages, Contribution to Special issue of Pramana on Raychaudhuri
Equation at Cross-roads, edited by Naresh Dadhich, Pankaj Joshi and Probir
Ro
On the measure of spacetime and gravity
By following the general guiding principle that nothing should be prescribed
or imposed on the universal entity, spacetime, we establish that it is the
homogeneity (by which we mean homogeneity and isotropy of space and homogeneity
of time) that requires not only a universally constant invariant velocity but
also an invariant length given by its constant curvature, and
spacetime is completely free of dynamics. Thus and are the only
two true constants of the spacetime structure and no other physical constant
could claim this degree of fundamentalness. When matter is introduced, the
spacetime becomes inhomogeneous and dynamic, and its curvature then determines
by the Bianchi differential identity the equation of motion for the Einstein
gravity. The homogeneity thus demands that the natural state of \textit{free
spacetime} is of constant curvature and the cosmological constant thus emerges
as a clear prediction which seems to be borne out by the observations of
accelerating expansion of the Universe. However it has no relation to the
vacuum energy and it could be envisioned that in terms of the Planck area the
Universe measures units!Comment: 5 pages, revtex, Received Honorable Mention in the 2011 Gravity
Research Foundation Awards for Essays on Gravitatio
The most general axially symmetric electrovac spacetime adimitting separable equations of motion
We obtain the most general solution of the Einstein electro - vacuum equation
for the stationary axially symmetric spacetime in which the Hamilton-Jacobi and
Klein - Gordon equations are separable. The most remarkable feature of the
solution is its invariance under the duality transformation involving mass and
NUT parameter, and the radial and angle coordinates. It is the general solution
for a rotating (gravitational dyon) particle which is endowed with both
gravoelectric and gravomagnetic charges, and there exists a duality
transformation from one to the other. It also happens to be a transform of the
Kerr - NUT solution. Like the Kerr family, it is also possible to make this
solution radiating which asymptotically conforms to the Vaidya null radiation.Comment: 9 pages, RevTex, Accepted by Class. Quantum Grav. Title, Abstract and
some expressions have been modified, typos corrected. The solution and main
result remain unaltere
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