9,698 research outputs found
Thermodynamics of toroidal black holes
The thermodynamical properties of toroidal black holes in the grand canonical
ensemble are investigated using York's formalism. The black hole is enclosed in
a cavity with finite radius where the temperature and electrostatic potential
are fixed. The boundary conditions allow one to compute the relevant
thermodynamical quantities, e.g. thermal energy, entropy and specific heat.
This black hole is thermodynamically stable and dominates the grand partition
function. This means that there is no phase transition, as the one encountered
for spherical black holes.Comment: 11 pages, 2 eps figures, revte
Some remarks on singularities in quantum cosmology
We discuss to what extent classical singularities persist upon quantization
in two simple cosmological models.Comment: 4 pps., LaTeX2e. Substantial revisions. To appear in: Proc. of the
Second Conference on Constrained Dynamics and Quantum Gravity, Santa
Margherita Ligure, Italy, 17-21 September 1996. Edited by V. de Alfaro et a
Stationary Black Holes in a Generalized Three-Dimensional Theory of Gravity
We consider a generalized three-dimensional theory of gravity which is
specified by two fields, the graviton and the dilaton, and one parameter. This
theory contains, as particular cases, three-dimensional General Relativity and
three-dimensional String Theory. Stationary black hole solutions are generated
from the static ones using a simple coordinate transformation. The stationary
black holes solutions thus obtained are locally equivalent to the corresponding
static ones, but globally distinct. The mass and angular momentum of the
stationary black hole solutions are computed using an extension of the Regge
and Teitelboim formalism. The causal structure of the black holes is described.Comment: 12 pages, Late
Does a relativistic metric generalization of Newtonian gravity exist in 2+1 dimensions?
It is shown that, contrary to previous claims, a scalar tensor theory of
Brans-Dicke type provides a relativistic generalization of Newtonian gravity in
2+1 dimensions. The theory is metric and test particles follow the space-time
geodesics. The static isotropic solution is studied in vacuum and in regions
filled with an incompressible perfect fluid. It is shown that the solutions can
be consistently matched at the matter vacuum interface, and that the Newtonian
behavior is recovered in the weak field regime.Comment: 6 pages, no figures, Revtex4. Some discussions on the physical nature
of the interior solution and on the omega->infinity limit and some references
added. Version to appear in Phys. Rev.
The Two-Dimensional Analogue of General Relativity
General Relativity in three or more dimensions can be obtained by taking the
limit in the Brans-Dicke theory. In two dimensions
General Relativity is an unacceptable theory. We show that the two-dimensional
closest analogue of General Relativity is a theory that also arises in the
limit of the two-dimensional Brans-Dicke theory.Comment: 8 pages, LaTeX, preprint DF/IST-17.9
Collapsing shells of radiation in anti-de Sitter spacetimes and the hoop and cosmic censorship conjectures
Gravitational collapse of radiation in an anti-de Sitter background is
studied. For the spherical case, the collapse proceeds in much the same way as
in the Minkowski background, i.e., massless naked singularities may form for a
highly inhomogeneous collapse, violating the cosmic censorship, but not the
hoop conjecture. The toroidal, cylindrical and planar collapses can be treated
together. In these cases no naked singularity ever forms, in accordance with
the cosmic censorship. However, since the collapse proceeds to form toroidal,
cylindrical or planar black holes, the hoop conjecture in an anti-de Sitter
spacetime is violated.Comment: 4 pages, Revtex Journal: to appear in Physical Review
Exact General Relativistic Perfect Fluid Disks with Halos
Using the well-known ``displace, cut and reflect'' method used to generate
disks from given solutions of Einstein field equations, we construct static
disks made of perfect fluid based on vacuum Schwarzschild's solution in
isotropic coordinates. The same method is applied to different exactsolutions
to the Einstein'sequations that represent static spheres of perfect fluids. We
construct several models of disks with axially symmetric perfect fluid halos.
All disks have some common features: surface energy density and pressures
decrease monotonically and rapidly with radius. As the ``cut'' parameter
decreases, the disks become more relativistic, with surface energy density and
pressure more concentrated near the center. Also regions of unstable circular
orbits are more likely to appear for high relativistic disks. Parameters can be
chosen so that the sound velocity in the fluid and the tangential velocity of
test particles in circular motion are less then the velocity of light. This
tangential velocity first increases with radius and reaches a maximum.Comment: 22 pages, 25 eps.figs, RevTex. Phys. Rev. D to appea
The Three-Dimensional BTZ Black Hole as a Cylindrical System in Four-Dimensional General Relativity
It is shown how to transform the three dimensional BTZ black hole into a four
dimensional cylindrical black hole (i.e., black string) in general relativity.
This process is identical to the transformation of a point particle in three
dimensions into a straight cosmic string in four dimensions.Comment: Latex, 9 page
False vacuum decay: effective one-loop action for pair creation of domain walls
An effective one-loop action built from the soliton field itself for the
two-dimensional (2D) problem of soliton pair creation is proposed. The action
consists of the usual mass term and a kinetic term in which the simple
derivative of the soliton field is replaced by a covariant derivative. In this
effective action the soliton charge is treated no longer as a topological
charge but as a Noether charge. Using this effective one-loop action, the
soliton-antisoliton pair production rate is calculated and one recovers Stone's
exponential factor and the prefactor of Kiselev, Selivanov and Voloshin. The
results are also valid straightforwardly to the problem of pair creation rate
of domain walls in dimensions greater than 2.Comment: 12 pages, Late
- …