1,316 research outputs found
Thermodynamics of Quasi-Topological Cosmology
In this paper, we study thermodynamical properties of the apparent horizon in
a universe governed by quasi-topological gravity. Our aim is twofold. First, by
using the variational method we derive the general form of Friedmann equation
in quasi-topological gravity. Then, by applying the first law of thermodynamics
on the apparent horizon, after using the entropy expression associated with the
black hole horizon in quasi-topological gravity, and replacing the horizon
radius, , with the apparent horizon radius, , we derive
the corresponding Friedmann equation in quasi-topological gravity. We find that
these two different approaches yield the same result which show the profound
connection between the first law of thermodynamics and the gravitational field
equations of quasi-topological gravity. We also study the validity of the
generalized second law of thermodynamics in quasi-topological cosmology. We
find that, with the assumption of the local equilibrium hypothesis, the
generalized second law of thermodynamics is fulfilled for the universe
enveloped by the apparent horizon for the late time cosmology.Comment: 8 pages, no figure, Phys. Lett B, in press (2013
Thermodynamics of Rotating Black Branes in Gauss-Bonnet-Born-Infeld Gravity
Considering both the Gauss-Bonnet and the Born-Infeld terms, which are on
similar footing with regard to string corrections on the gravity side and
electrodynamic side, we present a new class of rotating solutions in
Gauss-Bonnet gravity with rotation parameters in the presence of a
nonlinear electromagnetic field. These solutions, which are asymptotically
anti-de Sitter in the presence of cosmological constant, may be interpreted as
black brane solutions with inner and outer event horizons, an extreme black
brane or naked singularity provided the metric parameters are chosen suitably.
We calculate the finite action and conserved quantities of the solutions by
using the counterterm method, and find that these quantities do not depend on
the Gauss-Bonnet parameter. We also compute the temperature, the angular
velocities, the electric charge and the electric potential. Then, we calculate
the entropy of the black brane through the use of Gibbs-Duhem relation and show
that it obeys the area law of entropy. We obtain a Smarr-type formula for the
mass as a function of the entropy, the angular momenta and the charge, and show
that the conserved and thermodynamic quantities satisfy the first law of
thermodynamics. Finally, we perform a stability analysis in both the canonical
and grand-canonical ensemble and show that the presence of a nonlinear
electromagnetic field has no effect on the stability of the black branes, and
they are stable in the whole phase space.Comment: 17 pages, one figur
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