3,245 research outputs found
Stellar Equilibrium in 2+1 Dimensions
The hydrostatic equilibrium of a dimensional perfect fluid star in
asymptotically anti-de Sitter space is discussed. The interior geometry matches
the exterior black-hole solution. An upper mass limit is found, analogous
to Buchdahl's theorem in 3+1, and the possibility of collapse is discussed. The
case of a uniform matter density is solved exactly and a new interior solution
is presented.Comment: 11 pages, revtex, no figure
Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions
We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.Comment: Accepted for publication in CQ
Field Theory as Free Fall
It is shown that the classical field equations pertaining to gravity coupled
to other bosonic fields are equivalent to a single geodesic equation,
describing the free fall of a point particle in superspace. Some implications
for quantum gravity are discussed.Comment: 18 pages, plain late
Linearized Gravity in Brane Backgrounds
A treatment of linearized gravity is given in the Randall-Sundrum background.
The graviton propagator is found in terms of the scalar propagator, for which
an explicit integral expression is provided. This reduces to the
four-dimensional propagator at long distances along the brane, and provides
estimates of subleading corrections. Asymptotics of the propagator off the
brane yields exponential falloff of gravitational fields due to matter on the
brane. This implies that black holes bound to the brane have a "pancake"-like
shape in the extra dimension, and indicates validity of a perturbative
treatment off the brane. Some connections with the AdS/CFT correspondence are
described.Comment: 31 pages, harvmac. v2: minor typo and reference corrections. v3:
minor corrections to eqs and discussio
Spherical and planar three-dimensional anti-de Sitter black holes
The technique of dimensional reduction was used in a recent paper (Zanchin et
al, Phys. Rev. D66, 064022,(2002)) where a three-dimensional (3D)
Einstein-Maxwell-Dilaton theory was built from the usual four-dimensional (4D)
Einstein-Maxwell-Hilbert action for general relativity. Starting from a class
of 4D toroidal black holes in asymptotically anti-de Sitter (AdS) spacetimes
several 3D black holes were obtained and studied in such a context. In the
present work we choose a particular case of the 3D action which presents
Maxwell field, dilaton field and an extra scalar field, besides gravity field
and a negative cosmological constant, and obtain new 3D static black hole
solutions whose horizons may have spherical or planar topology. We show that
there is a 3D static spherically symmetric solution analogous to the 4D
Reissner-Nordstr\"om-AdS black hole, and obtain other new 3D black holes with
planar topology. From the static spherical solutions, new rotating 3D black
holes are also obtained and analyzed in some detail.Comment: 27 pages, uses "iopclass" files (Latex2e
Strong Brane Gravity and the Radion at Low Energies
For the 2-brane Randall-Sundrum model, we calculate the bulk geometry for
strong gravity, in the low matter density regime, for slowly varying matter
sources. This is relevant for astrophysical or cosmological applications. The
warped compactification means the radion can not be written as a homogeneous
mode in the orbifold coordinate, and we introduce it by extending the
coordinate patch approach of the linear theory to the non-linear case. The
negative tension brane is taken to be in vacuum. For conformally invariant
matter on the positive tension brane, we solve the bulk geometry as a
derivative expansion, formally summing the `Kaluza-Klein' contributions to all
orders. For general matter we compute the Einstein equations to leading order,
finding a scalar-tensor theory with ,
and geometrically interpret the radion. We comment that this radion scalar may
become large in the context of strong gravity with low density matter.
Equations of state allowing to be negative, can exhibit behavior
where the matter decreases the distance between the 2 branes, which we
illustrate numerically for static star solutions using an incompressible fluid.
For increasing stellar density, the branes become close before the upper mass
limit, but after violation of the dominant energy condition. This raises the
interesting question of whether astrophysically reasonable matter, and initial
data, could cause branes to collide at low energy, such as in dynamical
collapse.Comment: 24 pages, 3 figure
Two dimensional general covariance from three dimensions
A 3d generally covariant field theory having some unusual properties is
described. The theory has a degenerate 3-metric which effectively makes it a 2d
field theory in disguise. For 2-manifolds without boundary, it has an infinite
number of conserved charges that are associated with graphs in two dimensions
and the Poisson algebra of the charges is closed. For 2-manifolds with boundary
there are additional observables that have a Kac-Moody Poisson algebra. It is
further shown that the theory is classically integrable and the general
solution of the equations of motion is given. The quantum theory is described
using Dirac quantization, and it is shown that there are quantum states
associated with graphs in two dimensions.Comment: 10 pages (Latex), Alberta-Thy-19-9
Cosmological scaling solutions of minimally coupled scalar fields in three dimensions
We examine Friedmann-Robertson-Walker models in three spacetime dimensions.
The matter content of the models is composed of a perfect fluid, with a
-law equation of state, and a homogeneous scalar field minimally
coupled to gravity with a self-interacting potential whose energy density
red-shifts as , where a denotes the scale factor. Cosmological
solutions are presented for different range of values of and .
The potential required to agree with the above red-shift for the scalar field
energy density is also calculated.Comment: LaTeX2e, 11 pages, 4 figures. To be published in Classical and
Quantum Gravit
- …