7,187 research outputs found
Black string corrections in variable tension braneworld scenarios
Braneworld models with variable tension are investigated, and the corrections
on the black string horizon along the extra dimension are provided. Such
corrections are encrypted in additional terms involving the covariant
derivatives of the variable tension on the brane, providing profound
consequences concerning the black string horizon variation along the extra
dimension, near the brane. The black string horizon behavior is shown to be
drastically modified by the terms corrected by the brane variable tension. In
particular, a model motivated by the phenomenological interesting case
regarding Eotvos branes is investigated. It forthwith provides further physical
features regarding variable tension braneworld scenarios, heretofore concealed
in all previous analysis in the literature. All precedent analysis considered
uniquely the expansion of the metric up to the second order along the extra
dimension, what is able to evince solely the brane variable tension absolute
value. Notwithstanding, the expansion terms aftermath, further accomplished in
this paper from the third order on, elicits the successive covariant
derivatives of the brane variable tension, and their respective coupling with
the extrinsic curvature, the Weyl tensor, and the Riemann and Ricci tensors, as
well as the scalar curvature. Such additional terms are shown to provide sudden
modifications in the black string horizon in a variable tension braneworld
scenarioComment: 12 pages, 5 figures, accepted in PR
Capim corrente: opção para criação animal a pasto no semiárido.
bitstream/item/115055/1/midia-Capim.pd
Gravitational pressure on event horizons and thermodynamics in the teleparallel framework
The concept of gravitational pressure is naturally defined in the context of
the teleparallel equivalent of general relativity. Together with the definition
of gravitational energy, we investigate the thermodynamics of rotating black
holes in the teleparallel framework. We obtain the value of the gravitational
pressure over the external event horizon of the Kerr black hole, and write an
expression for the thermodynamic relation , where the variations
refer to the Penrose process for the Kerr black hole. We employ only the
notions of gravitational energy and pressure that arise in teleparallel
gravity, and do not make any consideration of the area or the variation of the
area of the event horizon. However, our results are qualitatively similar to
the standard expression of the literature.Comment: 17 pages, 6 figure
Variations of the Energy of Free Particles in the pp-Wave Spacetimes
We consider the action of exact plane gravitational waves, or pp-waves, on
free particles. The analysis is carried out by investigating the variations of
the geodesic trajectories of the particles, before and after the passage of the
wave. The initial velocities of the particles are non-vanishing. We evaluate
numerically the Kinetic energy per unit mass of the free particles, and obtain
interesting, quasi-periodic behaviour of the variations of the Kinetic energy
with respect to the width of the gaussian that represents the wave.
The variation of the energy of the free particle is expected to be exactly
minus the variation of the energy of the gravitational field, and therefore
provides an estimation of the local variation of the gravitational energy. The
investigation is carried out in the context of short bursts of gravitational
waves, and of waves described by normalised gaussians, that yield impulsive
waves in a certain limit.Comment: 20 pages, 18 figures, further arguments supporting the localizability
of the gravitational energy are presented, published in Univers
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
- …