804 research outputs found
A note on Friedmann equation of FRW universe in deformed Horava-Lifshitz gravity from entropic force
With entropic interpretation of gravity proposed by Verlinde, we obtain the
Friedmann equation of the Friedmann-Robertson-Walker universe for the deformed
Ho\v{r}ava-Lifshitz gravity. It is shown that, when the parameter of
Ho\v{r}ava-Lifshitz gravity , the modified Friedmann
equation will go back to the one in Einstein gravity. This results may imply
that the entropic interpretation of gravity is effective for the deformed
Ho\v{r}ava-Lifshitz gravity.Comment: 9 pages, no figure
Gauss-Bonnet Black Holes in dS Spaces
We study the thermodynamic properties associated with black hole horizon and
cosmological horizon for the Gauss-Bonnet solution in de Sitter space. When the
Gauss-Bonnet coefficient is positive, a locally stable small black hole appears
in the case of spacetime dimension , the stable small black hole
disappears and the Gauss-Bonnet black hole is always unstable quantum
mechanically when . On the other hand, the cosmological horizon is
found always locally stable independent of the spacetime dimension. But the
solution is not globally preferred, instead the pure de Sitter space is
globally preferred. When the Gauss-Bonnet coefficient is negative, there is a
constraint on the value of the coefficient, beyond which the gravity theory is
not well defined. As a result, there is not only an upper bound on the size of
black hole horizon radius at which the black hole horizon and cosmological
horizon coincide with each other, but also a lower bound depending on the
Gauss-Bonnet coefficient and spacetime dimension. Within the physical phase
space, the black hole horizon is always thermodynamically unstable and the
cosmological horizon is always stable, further, as the case of the positive
coefficient, the pure de Sitter space is still globally preferred. This result
is consistent with the argument that the pure de Sitter space corresponds to an
UV fixed point of dual field theory.Comment: Rextex, 17 pages including 8 eps figures, v2: minor changes, to
appear in PRD, v3: references adde
Null particle solutions in three-dimensional (anti-) de Sitter spaces
We obtain a class of exact solutions representing null particles moving in three-dimensional (anti-) de Sitter spaces by boosting the corresponding static point source solutions given by Deser and Jackiw. In de Sitter space the resulting solution describes two null particles moving on the (circular) cosmological horizon, while in anti-de Sitter space it describes a single null particle propagating from one side of the universe to the other. We also boost the Banados-Teitelboim-Zanelli black hole solution to the ultrarelativistic limit and obtain the solution for a spinning null particle moving in anti-de Sitter space. We find that the ultrarelativistic geometry of the black hole is exactly the same as that resulting from boosting the Deser-Jackiw solution when the angular momentum of the hole vanishes. A general class of solutions is also obtained which represents several null particles propagating in the Deser-Jackiw background. The differences between the three-dimensional and four-dimensional cases are also discussed
Black holes in the Einstein -Gauss-Bonnet theory and the geometry of their thermodynamics-II
In the present work we study (i) charged black hole in Einstein-Gauss-Bonnet
(EGB) theory, known as Einstein-Maxwell-Gauss-Bonnet (EMGB) black hole and (ii)
black hole in EGB gravity with Yang-Mills field. The thermodynamic geometry of
these two black hole solutions has been investigated, using the modified
entropy in Gauss-Bonnet theory.Comment: 7 page
Validity of the Generalized Second Law of Thermodynamics of the Universe Bounded by the Event Horizon in Brane Scenario
In this paper, we examine the validity of the generalized second law of
thermodynamics (GSLT) of the universe bounded by the event horizon in
brane-world gravity. Here we consider homogeneous and isotropic model of the
universe filled with perfect fluid in one case and in another case holographic
dark energy model of the universe has been considered. The conclusions are
presented point wise.Comment: 8 pages, the paper has been accepted in EPJC for publication.
Conclusion has been modified an some references have been adde
The thermodynamic evolution of the cosmological event horizon
By manipulating the integral expression for the proper radius of the
cosmological event horizon (CEH) in a Friedmann-Robertson-Walker (FRW)
universe, we obtain an analytical expression for the change \dd R_e in
response to a uniform fluctuation \dd\rho in the average cosmic background
density . We stipulate that the fluctuation arises within a vanishing
interval of proper time, during which the CEH is approximately stationary, and
evolves subsequently such that \dd\rho/\rho is constant. The respective
variations 2\pi R_e \dd R_e and \dd E_e in the horizon entropy and
enclosed energy should be therefore related through the cosmological
Clausius relation. In that manner we find that the temperature of the CEH
at an arbitrary time in a flat FRW universe is , which recovers
asymptotically the usual static de Sitter temperature. Furthermore, it is
proven that during radiation-dominance and in late times the CEH conforms to
the fully dynamical First Law T_e \drv S_e = P\drv V_e - \drv E_e, where
is the enclosed volume and is the average cosmic pressure.Comment: 6 page
Intertwined Order and Holography: The Case of Parity Breaking Pair Density Waves
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Intertwined Order and Holography: The Case of Parity Breaking Pair Density Waves
Article / Letter to editorLeids Instituut Onderzoek Natuurkund
Entropic force and its cosmological implications
We investigate a possibility of realizing the entropic force into the
cosmology. A main issue is how the holographic screen is implemented in the
Newtonian cosmology. Contrary to the relativistic realization of Friedmann
equations, we do not clarify the connection between Newtonian cosmology and
entropic force because there is no way of implementing the holographic screen
in the Newtonian cosmology.Comment: 16 pages, no figures, version "Accepted for publication in
Astrophysics & Space Science
Generalized Second Law of Thermodynamics in Extended Theories of Gravity
By employing the general expression of temperature
associated with the apparent horizon of a FRW universe and assuming a region of
FRW universe enclosed by the apparent horizon as a thermal system in
equilibrium, we are able to show that the generalized second law of
thermodynamics holds in Gauss-Bonnet gravity and in more general Lovelock
gravity.Comment: 10 page
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