86,044 research outputs found
Brane bounce-type configurations in a string-like scenario
Brane world six dimensional scenarios with string like metric has been
proposed to alleviate the problem of field localization. However, these models
have been suffering from some drawbacks related with energy conditions as well
as from difficulties to find analytical solutions. In this work, we propose a
model where a brane is made of a scalar field with bounce-type configurations
and embedded in a bulk with a string-like metric. This model produces a sound
AdS scenario where none of the important physical quantities is infinite. Among
these quantities are the components of the energy momentum tensor, which have
its positivity ensured by a suitable choice of the bounce configurations.
Another advantage of this model is that the warp factor can be obtained
analytically from the equations of motion for the scalar field, obtaining as a
result a thick brane configuration, in a six dimensional context. Moreover, the
study of the scalar field localization in these scenario is done.Comment: 15 pages, 5 figures. To appear in Physics Letters
Euclidean analysis of the entropy functional formalism
The attractor mechanism implies that the supersymmetric black hole near
horizon solution is defined only in terms of the conserved charges and is
therefore independent of asymptotic moduli. Starting only with the near horizon
geometry, Sen's entropy functional formalism computes the entropy of an extreme
black hole by means of a Legendre transformation where the electric fields are
defined as conjugated variables to the electric charges. However, traditional
Euclidean methods require the knowledge of the full geometry to compute the
black hole thermodynamic quantities. We establish the connection between the
entropy functional formalism and the standard Euclidean formalism taken at zero
temperature. We find that Sen's entropy function 'f' (on-shell) matches the
zero temperature limit of the Euclidean action. Moreover, Sen's near horizon
angular and electric fields agree with the chemical potentials that are defined
from the zero-temperature limit of the Euclidean formalism.Comment: 37 pages. v3: Footnote and Reference added. Published versio
On FRW Model in Conformal Teleparallel Gravity
In this paper we use the conformal teleparallel gravity to study an isotropic
and homogeneous Universe which is settled by the FRW metric. We solve the field
equations and we obtain the behavior of some cosmological parameters such as
scale factor, deceleration parameter and the energy density of the perfect
fluid which is the matter field of our model. The field equations, that we
called modified Friedmann equations, allow us to define a dark fluid, with dark
energy density and dark pressure, responsible for the acceleration in the
Universe.Comment: Accepted in EPJ
Quantum anisotropic Heisenberg chains with superlattice structure: a DMRG study
Using the density matrix renormalization group technique, we study spin
superlattices composed of a repeated pattern of two spin-1/2 XXZ chains with
different anisotropy parameters. The magnetization curve can exhibit two
plateaus, a non trivial plateau with the magnetization value given by the
relative sizes of the sub-chains and another trivial plateau with zero
magnetization. We find good agreement of the value and the width of the
plateaus with the analytical results obtained previously. In the gapless
regions away from the plateaus, we compare the finite-size spin gap with the
predictions based on bosonization and find reasonable agreement. These results
confirm the validity of the Tomonaga-Luttinger liquid superlattice description
of these systems.Comment: 6 pages, 6 figure
- …