81 research outputs found
Gravitational Geons on the Brane
In this paper, we examine the possibility of static, spherically symmetric
gravitational geons on a 3 dimensional brane embedded in a 4+1 dimensional
space-time. We choose a specific g_tt for the brane-world space-time metric. We
then calculate g_rr analytically in the weak field limit and numerically for
stronger fields. We show that the induced field equations on the brane do admit
gravitational geon solutions.Comment: 14 pages with 9 figures. To appear in General Relativity and
Gravitatio
Dynamical compactification from de Sitter space
We show that D-dimensional de Sitter space is unstable to the nucleation of
non-singular geometries containing spacetime regions with different numbers of
macroscopic dimensions, leading to a dynamical mechanism of compactification.
These and other solutions to Einstein gravity with flux and a cosmological
constant are constructed by performing a dimensional reduction under the
assumption of q-dimensional spherical symmetry in the full D-dimensional
geometry. In addition to the familiar black holes, black branes, and
compactification solutions we identify a number of new geometries, some of
which are completely non-singular. The dynamical compactification mechanism
populates lower-dimensional vacua very differently from false vacuum eternal
inflation, which occurs entirely within the context of four-dimensions. We
outline the phenomenology of the nucleation rates, finding that the
dimensionality of the vacuum plays a key role and that among vacua of the same
dimensionality, the rate is highest for smaller values of the cosmological
constant. We consider the cosmological constant problem and propose a novel
model of slow-roll inflation that is triggered by the compactification process.Comment: Revtex. 41 pages with 24 embedded figures. Minor corrections and
added reference
U(1) Gauge Field of the Kaluza-Klein Theory in the Presence of Branes
We investigate the zero mode dimensional reduction of the Kaluza-Klein
unifications in the presence of a single brane in the infinite extra dimension.
We treat the brane as fixed, not a dynamical object, and do not require the
orbifold symmetry. It seems that, contrary to the standard Kaluza-Klein models,
the 4D effective action is no longer invariant under the U(1) gauge
transformations due to the explicit breaking of isometries in the extra
dimension by the brane. Surprisingly, however, the linearized perturbation
analysis around the RS vacuum shows that the Kaluza-Klein gauge field does
possess the U(1) gauge symmetry at the linear level. In addition, the
graviscalar also behaves differently from the 4D point of view. Some physical
implications of our results are also discussed.Comment: 10 pages, revtex, no figure, version to appear in Phys. Rev. D,
possible caveats of our results due to the zero mode ansatz we used are
explained in more detai
Bosonic Fields in the String-like Defect Model
We study localization of bosonic bulk fields on a string-like defect with
codimension 2 in a general space-time dimension in detail. We show that in
cases of spin 0 scalar and spin 1 vector fields there are an infinite number of
massless Kaluza-Klein (KK) states which are degenerate with respect to the
radial quantum number, but only the massless zero mode state among them is
coupled to fermion on the string-like defect. It is also commented on
interesting extensions of the model at hand to various directions such as
'little' superstring theory, conformal field theory and a supersymmetric
construction.Comment: 17 pages, LaTex 2e, revised version (to appear in Phys. Rev. D
The Deformable Universe
The concept of smooth deformations of a Riemannian manifolds, recently
evidenced by the solution of the Poincar\'e conjecture, is applied to
Einstein's gravitational theory and in particular to the standard FLRW
cosmology. We present a brief review of the deformation of Riemannian geometry,
showing how such deformations can be derived from the Einstein-Hilbert
dynamical principle. We show that such deformations of space-times of general
relativity produce observable effects that can be measured by four-dimensional
observers. In the case of the FLRW cosmology, one such observable effect is
shown to be consistent with the accelerated expansion of the universe.Comment: 20 pages, LaTeX, 3 figure
Magnetized Particle Capture Cross Section for Braneworld Black Hole
Capture cross section of magnetized particle (with nonzero magnetic moment)
by braneworld black hole in uniform magnetic field is considered. The magnetic
moment of particle was chosen as it was done by \citet{rs99} and for the
simplicity particle with zero electric charge is chosen. It is shown that the
spin of particle as well as the brane parameter are to sustain the stability of
particles circularly orbiting around the black hole in braneworld i.e. spin of
particles and brane parameter try to prevent the capture by black hole.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space
Scienc
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
Einstein equations for an asymmetric brane-world
We consider a brane-world of co-dimension one without the reflection symmetry
that is commonly imposed between the two sides of the brane. Using the
coordinate-free formalism of the Gauss-Codacci equations, we derive the
effective Einstein equations by relating the local curvature to the matter on
the brane in the case when its bare tension is much larger than the localized
matter, and hence show that Einstein gravity is a natural consequence of such
models in the weak field limit. We find agreement with the recently derived
cosmological case, which can be solved exactly, and point out that such models
can be realized naturally in the case where there is a minimally coupled form
field in the bulk.Comment: 14 pages, Revte
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