1,654 research outputs found
Brane Cosmology in an Arbitrary Number of Dimensions
We derive the effective cosmological equations for a non-
symmetric codimension one brane embedded in an arbitrary D-dimensional bulk
spacetime, generalizing the cases much studied previously. As a
particular case, this may be considered as a regularized codimension (D-4)
brane avoiding the problem of curvature divergence on the brane. We apply our
results to the case of spherical symmetry around the brane and to partly
compactified AdS-Schwarzschild bulks.Comment: 23 page
Brane Isotropisation in Extra-Dimensional Tolman-Bondi Universe
We consider the dynamics of a 3-brane embedded in an extra-dimensional
Tolman-Bondi Universe where the origin of space plays a special role. The
embedding is chosen such that the induced matter distribution on the brane
respects the spherical symmetry of matter in the extra dimensional space. The
mirage cosmology on the probe brane is studied, resulting in an inhomogeneous
and anisotropic four dimensional cosmology where the origin of space is also
special. We then focus on the spatial geometry around the origin and show that
the induced geometry, which is initially inhomogeneous and anisotropic,
converges to an isotropic and homogeneous Friedmann-Lemaitre 4d space-time. For
instance, when a 3-brane is embedded in a 5d matter dominated model, the 4d
dynamics around the origin converge to a Friedmann-Lemaitre Universe in a
radiation dominated epoch. We analyse this isotropisation process and show that
it is a late time attractor.Comment: 16 pages, 8 figures, one reference adde
Black Rings, Boosted Strings and Gregory-Laflamme
We investigate the Gregory-Laflamme instability for black strings carrying
KK-momentum along the internal direction. We demonstrate a simple kinematical
relation between the thresholds of the classical instability for the boosted
and static black strings. We also find that Sorkin's critical dimension depends
on the internal velocity and in fact disappears for sufficiently large boosts.
Our analysis implies the existence of an analogous instability for the
five-dimensional black ring of Emparan and Reall. We also use our results for
boosted black strings to construct a simple model of the black ring and argue
that such rings exist in any number of space-time dimensions.Comment: 26 pages, 6 figure
Parameterized Post-Newtonian coefficients for Brans-Dicke gravity with d+1 dimensions
We present calculations of Post-Newtonian parameters for Brans-Dicke
tensor-scalar gravity in an arbitrary number of compact extra dimensions in
both the Jordan and Einstein conformal frames. We find that the parameter
gamma, which measures the amount of spacetime curvature per unit mass, becomes
a function of omega, the coefficient of the scalar kinetic term in the
Brans-Dicke Lagrangian. Experiment has placed strong constraints on gamma which
require that omega become negative in the Jordan frame for any number of extra
dimensions, highlighting that this formulation is not physical. We also confirm
the well-known result that a compact extra dimension can be equivalently viewed
as a massless scalar `dilaton.' In the Einstein frame, we find that the
behavior of gamma as constrained by experiment replicates that which is
predicted by string theory.Comment: 9 pages, accepted in Classical and Quantum Gravit
Modified Newton's law, braneworlds, and the gravitational quantum well
Most of the theories involving extra dimensions assume that only the
gravitational interaction can propagate in them. In such approaches, called
brane world models, the effective, 4-dimensional, Newton's law is modified at
short as well as at large distances. Usually, the deformation of Newton's law
at large distances is parametrized by a Yukawa potential, which arises mainly
from theories with compactified extra dimensions. In many other models however,
the extra dimensions are infinite. These approaches lead to a large distance
power-law deformation of the gravitational newtonian potential , namely
, which is less studied in the literature. We
investigate here the dynamics of a particle in a gravitational quantum well
with such a power-law deformation. The effects of the deformation on the energy
spectrum are discussed. We also compare our modified spectrum to the results
obtained with the GRANIT experiment, where the effects of the Earth's
gravitational field on quantum states of ultra cold neutrons moving above a
mirror are studied. This comparison leads to upper bounds on and .Comment: 11 pages, 1 figur
Inducing charges and currents from extra dimensions
In a particular variant of Kaluza-Klein theory, the so-called induced-matter
theory (IMT), it is shown that any configuration of matter may be geometrically
induced from a five-dimensional vacuum space. By using a similar approach we
show that any distribution of charges and currents may also be induced from a
five-dimensional vacuum space. Whereas in the case of IMT the geometry is
Riemannian and the fundamental equations are the five-dimensional Einstein
equations in vacuum, here we consider a Minkowskian geometry and the
five-dimensional Maxwell equations in vacuum.Comment: 8 pages. Accepted for publication in Modern Physics Letters
All-optical measurement of the hot electron sheath driving laser ion acceleration from thin foils
We present experimental results from an all-optical diagnostic method to directly measure the evolution of the hot-electron distribution driving the acceleration of ions from thin foils using high-intensity lasers. Central parameters of laser ion acceleration such as the hot-electron density, the temperature distribution and the conversion efficiency from laser pulse energy into hot electrons become comprehensively accessible with this technique.Deutsche Forschungsgemeinschaft (DFG) (contract number TR18)Germany. Bundesministerium für Bildung und Forschung (contract number 03ZIK445)Germany. Bundesministerium für Bildung und Forschung (contract number 03ZIK052
State-Relevant Maxwell's Equation from Kaluza-Klein Theory
We study a five-dimensional perfect fluid coupled with Kaluza-Klein (KK)
gravity. By dimensional reduction, a modified form of Maxwell's equation is
obtained, which is relevant to the equation of state of the source. Since the
relativistic magnetohydrodynamics (MHD) and the 3-dimensional formulation are
widely used to study space matter, we derive the modified Maxwell's equations
and relativistic MHD in 3+1 form. We then take an ideal Fermi gas as an example
to study the modified effect, which can be visible under high density or high
energy condition, while the traditional Maxwell's equation can be regarded as a
result in the low density and low temperature limit. We also indicate the
possibility to test the state-relevant effect of KK theory in a telluric
laboratory.Comment: 11 pages, 3 figures; version published in PR
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