2,050 research outputs found
First Order Semiclassical Thermal String in the AdS Spacetime
We formulate the finite temperature theory for the free thermal excitations
of the bosonic string in the anti-de Sitter (AdS) spacetime in the Thermo Field
Dynamics (TFD) approach. The spacetime metric is treated exactly while the
string and the thermal reservoir are semiclassically quantized at the first
order perturbation theory with respect to the dimensionless parameter \epsilon
= \a ' H^{-2}. In the conformal black-hole AdS background the
quantization is exact. The method can be extended to the arbitrary AdS
spacetime only in the first order perturbation. This approximation is taken in
the center of mass reference frame and it is justified by the fact that at the
first order the string dynamics is determined only by the interaction between
the {\em free} string oscillation modes and the {\em exact} background. The
first order thermal string is obtained by thermalization of the system
carried on by the TFD Bogoliubov operator. We determine the free thermal string
states and compute the local entropy and free energy in the center of mass
reference frame.Comment: Minor typos corrected. Two references added. LATeX file, 19 page
Quasi-homologous spherically symmetric branes and their symmetry breaking
We revisit the dynamical system based approach of spherically symmetric
vacuum braneworlds, pointing out and studying the existence of a transcritical
bifurcation as the dark pressure parameter changes its sign, we analyze some
consequences of not discard the brane cosmological constant. For instance, it
is noteworthy that the existence of an isothermal state equation between the
dark fluid parameters cannot be obtained via the requirement of a
quasi-homologous symmetry of the vacuum.Comment: 20 pages, 12 figures. To appear in EPJ
Solution for a local straight cosmic string in the braneworld gravity
In this work we deal with the spacetime shaped by a straight cosmic string,
emerging from local gauge theories, in the braneworld gravity context. We
search for physical consequences of string features due to the modified
gravitational scenario encoded in the projected gravitational equations. It is
shown that cosmic strings in braneworld gravity may present significant
differences when compared to the general relativity predictions since its
linear density is modified and the deficit angle produced by the cosmic string
is attenuated. Furthermore, the existence of cosmic strings in that scenario
requires a strong restriction to the braneworld tension: , in Planck units.Comment: 7 pages, 3 figure
Notes on the Two-brane Model with Variable Tension
Motivated by possible extensions of the braneworld models with two branes, we
investigate some consequences of a variable brane tension using the well
established results on consistency conditions. By a slight modification of the
usual stress-tensor used in order to derive the braneworld sum rules, we find
out some important constraints obeyed by time dependent brane tensions. In
particular it is shown that the tensions of two Randall-Sundrum like branes
obeying, at the same time, an Eotvos law, aggravate the fine tuning problem.
Also, it is shown that if the hidden brane tension obeys an Eotvos law, then
the visible brane has a mixed behavior allowing a bouncing-like period at early
times while it is dominated by an Eotvos law nowadays. To finalize, we discuss
some qualitative characteristics which may arise in the scope of dynamical
brane tensions, as anisotropic background and branons production.Comment: 7 pages, 1 figure, accepted for publication in Physical Review
Static Domain Wall in the Braneworld gravity
In this paper we consider a static domain wall inside a 3-brane. Differently
of the standard achievement obtained in General Relativity, the analysis
performed here gives a consistency condition for the existence of static domain
walls in a braneworld gravitational scenario. It is also shown the behavior of
the domain wall gravitational field in the newtonian limit.Comment: 11 pages, no figures, accepted for publication in EPJ
Brane Cosmic String Compactification in Brans-Dicke Theory
We investigate an alternative compactification of extra dimensions using
local cosmic string in the Brans-Dicke gravity framework. In the context of
dynamical systems it is possible to show that there exist a stable field
configuration for the Einstein-Brans-Dicke equations. We explore the analogies
between this particular model and the Randall-Sundrum scenario.Comment: RevTex, 5 pages, no figures. To appear in the Physical Review
Towards an hybrid compactification with a scalar-tensor global cosmic string
We derive a solution of the gravitational equations which leads to a
braneworld scenario in six dimensions using a global cosmic string solution in
a low energy effective string theory framework. The final spacetime is composed
by one warped brane with topology and a power
law warp factor, and one noncompact extra dimension transverse to the brane. By
looking at the current experimental bounds, we find a range of parameters in
which, if the on-brane dimension has an acceptable size, it does not solve the
hierarchy problem. In another example this problem is smoothed by the
Brans-Dicke parameter.Comment: RevTex, 7 pages. New version to be published in the JCAP (2008
On the motion of particles in covariant Horava-Lifshitz gravity and the meaning of the A-field
We studied the low energy motion of particles in the general covariant
version of Horava-Lifshitz gravity proposed by Horava and Melby-Thompson. Using
a scalar field coupled to gravity according to the minimal substitution recipe
proposed by da Silva and taking the geometrical optics limit, we could write an
effective relativistic metric for a general solution. As a result, we
discovered that the equivalence principle is not in general recovered at low
energies, unless the spatial Laplacian of A vanishes. Finally, we analyzed the
motion on the spherical symmetric solution proposed by Horava and
Melby-Thompson, where we could find its effective line element and compute
spin-0 geodesics. Using standard methods we have shown that such an effective
metric cannot reproduce Newton's gravity law even in the weak gravitational
field approximation.Comment: New result about equivalence principle added, improved discussion and
typos corrected. Version to appear in Phys. Lett.
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