3,408 research outputs found
Low Energy Effective Action for Horava-Witten Cosmology
As a supersymmetric extension of the Randall-Sundrum model, we consider a
5-dimensional Horava-Witten type theory, and derive its low energy effective
action. The model we consider is a two-brane system with a bulk scalar field
satisfying the BPS condition. We solve the bulk equations of motion using a
gradient expansion method, and substitute the solution into the original action
to get the 4-dimensional effective action. The resultant effective theory can
be casted into the form of Einstein gravity coupled with two scalar fields, one
arising from the radion, the degree of freedom of the inter-brane distance, and
the other from the bulk scalar field. We also clarify the relation between our
analysis and the moduli approximation.Comment: 11 page
Towards A Nonsingular Tachyonic Big Crunch
We discuss an effective field theory background containing the gravitational
field, the dilaton and a closed string tachyon, and couple this background to a
gas of fundamental strings and D strings. Allowing for the possibility of a
non-vanishing dilaton potential of Casimir type, we demonstrate the possibility
of obtaining a nonsingular, static tachyon condensate phase with fixed dilaton.
The time reversal of our solution provides a candidate effective field theory
description of a Hagedorn phase of string gas cosmology with fixed dilaton.Comment: 7 pages, two references adde
Electrochemical synthesis and properties of CoO2, the x = 0 phase of the AxCoO2 systems (A = Li, Na)
Single-phase bulk samples of the "exotic" CoO2, the x = 0 phase of the AxCoO2
systems (A = Li, Na), were successfully synthesized through electrochemical
de-intercalation of Li from pristine LiCoO2 samples. The samples of pure CoO2
were found to be essentially oxygen stoichiometric and possess a hexagonal
structure consisting of stacked triangular-lattice CoO2 layers only. The
magnetism of CoO2 is featured with a temperature-independent susceptibility of
the magnitude of 10-3 emu/mol Oe, being essentially identical to that of a
Li-doped phase, Li0.12CoO2. It is most likely that the CoO2 phase is a
Pauli-paramagnetic metal with itinerant electrons.Comment: 12 pages, 3 figure
Anisotropic Power-law Inflation
We study an inflationary scenario in supergravity model with a gauge kinetic
function. We find exact anisotropic power-law inflationary solutions when both
the potential function for an inflaton and the gauge kinetic function are
exponential type. The dynamical system analysis tells us that the anisotropic
power-law inflation is an attractor for a large parameter region.Comment: 14 pages, 1 figure. References added, minor corrections include
Black String Perturbations in RS1 Model
We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor . Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.Comment: 14 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
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