1,486 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
Thermodynamical study of FRW universe in Quasi-Topological Theory
By applying the unified first law of thermodynamics on the apparent horizon
of FRW universe, we get the entropy relation for the apparent horizon in
quasi-topological gravity theory. Throughout the paper, the results of
considering the Hayward-Kodama and Cai-Kim temperatures are also addressed. Our
study shows that whenever, there is no energy exchange between the various
parts of cosmos, we can get an expression for the apparent horizon entropy in
quasi-topological gravity, which is in agreement with other attempts followed
different approaches. The effects of a mutual interaction between the various
parts of cosmos on the apparent horizon entropy as well as the validity of
second law of thermodynamics in quasi-topological gravity are also perused.Comment: The text has been revised and some new references are adde
Charged Lifshitz Black Holes
We investigate modifications of the Lifshitz black hole solutions due to the
presence of Maxwell charge in higher dimensions for arbitrary and any
topology. We find that the behaviour of large black holes is insensitive to the
topology of the solutions, whereas for small black holes significant
differences emerge. We generalize a relation previously obtained for neutral
Lifshitz black branes, and study more generally the thermodynamic relationship
between energy, entropy, and chemical potential. We also consider the effect of
Maxwell charge on the effective potential between objects in the dual theory.Comment: Latex, 28 pages, 14 figures, some references adde
Hairy rotating black string in the Einstein-Maxwell-Higgs system
We show numerically that the Abelian Higgs field equations in the background
of a four-dimensional rotating charged black string have vortex solutions.
These solutions which have axial symmetry show that the rotating black string
can support the Abelian Higgs field as hair. We find that one encounters with
an electric field coupled to the Higgs scalar field for the case of rotating
black string. This electric field is due to an electric charge per unit length,
which increases as the rotation parameter becomes larger. We also find that the
vortex thickness decreases as the rotation parameter grows up. Finally we
consider the self-gravity of the Abelian Higgs field and show that the effect
of the vortex is to induce a deficit angle in the metric under consideration
which decreases as the rotation parameter increases.Comment: 16 pages, 8 figures, references added, some minor corrections don
Venomous Animals; Are They Important in Iran?
Many reports have indicated the medical importance of animal poisons in Iran. The significance numbers of Iranians are injured from high endemic to sporadic, by venomous snakes, scorpions, wasps, bees, fire and velvet ants, spiders and backswimmer bugs, so their nuisance prevention is an important task
- …