1,874 research outputs found
Second order brane cosmology with radion stabilization
We study cosmology in the five-dimensional Randall-Sundrum brane-world with a
stabilizing effective potential for the radion and matter localized on the
branes. The analysis is performed by employing a perturbative expansion in the
ratio rho/V between the matter energy density on the branes and the brane
tensions around the static Randall-Sundrum solution (which has rho=0 and brane
tensions +-V). This approach ensures that the matter evolves adiabatically and
allows us to find approximate solutions to second order in \rho/V. Some
particular cases are then analyzed in details.Comment: 17 pages, RevTeX4, 4 figures, final version to appear in Phys. Rev.
Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders
Several models predict the existence of heavy colored resonances decaying to
top quarks in the TeV energy range that might be discovered at the LHC. In some
of those models, moreover, a sizable charge asymmetry of top versus antitop
quarks might be generated. The detection of these exotic resonances, however,
requires selecting data samples where the top and the antitop quarks are highly
boosted, which is experimentally very challenging. We asses that the
measurement of the top quark charge asymmetry at the LHC is very sensitive to
the existence of excited states of the gluon with axial-vector couplings to
quarks. We use a toy model with general flavour independent couplings, and show
that a signal can be detected with relatively not too energetic top and antitop
quarks. We also compare the results with the asymmetry predicted by QCD, and
show that its highest statistical significance is achieved with data samples of
top-antitop quark pairs of low invariant masses.Comment: 20 page
Five-Dimensional Unification of the Cosmological Constant and the Photon Mass
Using a non-Riemannian geometry that is adapted to the 4+1 decomposition of
space-time in Kaluza-Klein theory, the translational part of the connection
form is related to the electromagnetic vector potential and a Stueckelberg
scalar. The consideration of a five-dimensional gravitational action functional
that shares the symmetries of the chosen geometry leads to a unification of the
four-dimensional cosmological term and a mass term for the vector potential.Comment: 8 pages, LaTe
Limits of space-times in five dimensions and their relation to the Segre Types
A limiting diagram for the Segre classification in 5-dimensional space-times
is obtained, extending a recent work on limits of the energy-momentum tensor in
general relativity. Some of Geroch's results on limits of space-times in
general relativity are also extended to the context of five-dimensional
Kaluza-Klein space-times.Comment: Late
A Note on Segre Types of Second Order Symmetric Tensors in 5-D Brane-world Cosmology
Recent developments in string theory suggest that there might exist extra
spatial dimensions, which are not small nor compact. The framework of most
brane cosmological models is that in which the matter fields are confined on a
brane-world embedded in five dimensions (the bulk). Motivated by this we
reexamine the classification of the second order symmetric tensors in 5--D, and
prove two theorems which collect together some basic results on the algebraic
structure of these tensors in 5-dimensional space-times. We also briefly
indicate how one can obtain, by induction, the classification of symmetric
two-tensors (and the corresponding canonical forms) on n-dimensional spaces
from the classification on 4-dimensional spaces. This is important in the
context of 11--D supergravity and 10--D superstrings.Comment: 12 pages, to appear in Mod. Phys. Lett. A (2003) in the present for
Brane world corrections to scalar vacuum force in RSII-p
Vacuum force is an interesting low energy test for brane worlds due to its
dependence on field's modes and its role in submillimeter gravity experiments.
In this work we generalize a previous model example: the scalar field vacuum
force between two parallel plates lying in the brane of a Randall-Sundrum
scenario extended by compact dimensions (RSII-). Upon use of Green's
function technique, for the massless scalar field, the 4D force is obtained
from a zero mode while corrections turn out attractive and depend on the
separation between plates as . For the massive scalar field a
quasilocalized mode yields the 4D force with attractive corrections behaving
like . Corrections are negligible w.r.t. 4D force for
radius less than m. Although the case is not
physically viable due to the different behavior in regard to localization for
the massless scalar and electromagnetic fields it yields an useful comparison
between the dimensional regularization and Green's function techniques as we
describe in the discussion.Comment: 14 pages, v2: discussion clarified, reference adde
Early Universe Constraints on Time Variation of Fundamental Constants
We study the time variation of fundamental constants in the early Universe.
Using data from primordial light nuclei abundances, CMB and the 2dFGRS power
spectrum, we put constraints on the time variation of the fine structure
constant , and the Higgs vacuum expectation value leads to a variation
in the electron mass, among other effects. Along the same line, we study the
variation of and the electron mass . In a purely phenomenological
fashion, we derive a relationship between both variations.Comment: 18 pages, 12 figures, accepted for publication in Physical Review
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
Doubly Special Relativity with a minimum speed and the Uncertainty Principle
The present work aims to search for an implementation of a new symmetry in
the space-time by introducing the idea of an invariant minimum speed scale
(). Such a lowest limit , being unattainable by the particles, represents
a fundamental and preferred reference frame connected to a universal background
field (a vacuum energy) that breaks Lorentz symmetry. So there emerges a new
principle of symmetry in the space-time at the subatomic level for very low
energies close to the background frame (), providing a fundamental
understanding for the uncertainty principle, i.e., the uncertainty relations
should emerge from the space-time with an invariant minimum speed.Comment: 10 pages, 8 figures, Correlated paper in:
http://www.worldscientific.com/worldscinet/ijmpd?journalTabs=read. arXiv
admin note: substantial text overlap with arXiv:physics/0702095,
arXiv:0705.4315, arXiv:0709.1727, arXiv:0805.120
The Real Scalar Field Equation for Nariai Black Hole in the 5D Schwarzschild-de Sitter Black String Space
The Nariai black hole, whose two horizons are lying close to each other, is
an extreme and important case in the research of black hole. In this paper we
study the evolution of a massless scalar field scattered around in 5D
Schwarzschild-de Sitter black string space. Using the method shown by Brevik
and Simonsen (2001) we solve the scalar field equation as a boundary value
problem, where real boundary condition is employed. Then with convenient
replacement of the 5D continuous potential by square barrier, the reflection
and transmission coefficients () are obtained. At last, we also compare
the coefficients with usual 4D counterpart.Comment: 10 pages,6 figures.To appear in Int. J. Mod. Phys.
- âŠ