1,683 research outputs found

### Hawking radiation from the cosmological horizon in a FRW universe

It is well known that there is a Hawking radiation from the cosmological
horizon of the de-sitter spacetime, and the de-sitter spacetime can be a
special case of a FRW universe. Therefore, there may be a corresponding Hawking
radiation in a FRW universe. Indeed, there have been several clues showing that
there is a Hawking radiation from the apparent horizon of a FRW universe. In
our paper, however, we find that the Hawking radiation may come from the
cosmological horizon. Moreover, we also find that the Hawking radiation from
the apparent horizon of a FRW universe in some previous works can be a special
case in our result, and the condition is that the variation rate of
cosmological horizon $\overset{.}{r}_{H}$ is zero. Note that, this condition is
also consistent with the underlying integrable condition in these works from
the apparent horizon.Comment: V3: 12 pages, no figure, typos corrected, new references added,
version shorted and accepted by PL

### Gravity/Fluid Correspondence and Its Application on Bulk Gravity with $U(1)$ Gauge Field

As the long wavelength limit of the AdS/CFT correspondence, the gravity/fluid
correspondence has been shown to be a useful tool for extracting properties of
the fluid on the boundary dual to the gravity in the bulk. In this paper, after
briefly reviewing the algorithm of gravity/fluid correspondence, we discuss the
results of its application on bulk gravity with a $U(1)$ gauge field. In the
presence of a $U(1)$ gauge field, the dual fluid possesses more interesting
properties such as its charge current. Furthermore, an external field
$A_\mu^{ext}$ could affect the charge current, and the $U(1)$ Chern-Simons term
also reinduces extra structures to the dual current giving anomalous transport
coefficients.Comment: 14 pages, no figure, version publishe

### Bulk Viscosity of dual Fluid at Finite Cutoff Surface via Gravity/Fluid correspondence in Einstein-Maxwell Gravity

Based on the previous paper arXiv:1207.5309, we investigate the possibility
to find out the bulk viscosity of dual fluid at the finite cutoff surface via
gravity/fluid correspondence in Einstein-Maxwell gravity. We find that if we
adopt new conditions to fix the undetermined parameters contained in the stress
tensor and charged current of the dual fluid, two new terms appear in the
stress tensor of the dual fluid. One new term is related to the bulk viscosity
term, while the other can be related to the perturbation of energy density. In
addition, since the parameters contained in the charged current are the same,
the charged current is not changed.Comment: 15 pages, no figure, typos corrected, new references and comments
added, version accepted by PL

### The effects of massive graviton on the equilibrium between the black hole and radiation gas in an isolated box

It is well known that the black hole can has temperature and radiate the
particles with black body spectrum, i.e. Hawking radiation. Therefore, if the
black hole is surrounded by an isolated box, there is a thermal equilibrium
between the black hole and radiation gas. A simple case considering the thermal
equilibrium between the Schwarzschild black hole and radiation gas in an
isolated box has been well investigated previously in detail, i.e. taking the
conservation of energy and principle of maximal entropy for the isolated system
into account. In this paper, following the above spirit, the effects of massive
graviton on the thermal equilibrium will be investigated. For the gravity with
massive graviton, we will use the de Rham-Gabadadze-Tolley (dRGT) massive
gravity which has been proven to be ghost free. Because the graviton mass
depends on two parameters in the dRGT massive gravity, here we just investigate
two simple cases related to the two parameters, respectively. Our results show
that in the first case the massive graviton can suppress or increase the
condensation of black hole in the radiation gas although the $T-E$ diagram is
similar like the Schwarzschild black hole case. For the second case, a new
$T-E$ diagram has been obtained. Moreover, an interesting and important
prediction is that the condensation of black hole just increases from the zero
radius of horizon in this case, which is very different from the Schwarzschild
black hole case.Comment: 9 pages, 4 figure

### Generalized Vaidya Solutions and Misner-Sharp mass for $n$-dimensional massive gravity

Dynamical solutions are always of interest to people in gravity theories. We
derive a series of generalized Vaidya solutions in the $n$-dimensional de
Rham-Gabadadze-Tolley (dRGT) massive gravity with a singular reference metric.
Similar to the case of the Einstein gravity, the generalized Vaidya solution
can describe shining/absorbing stars. Moreover, we also find a more general
Vaidya-like solution by introducing a more generic matter field than the pure
radiation in the original Vaidya spacetime. As a result, the above generalized
Vaidya solution is naturally included in this Vaidya-like solution as a special
case. We investigate the thermodynamics for this Vaidya-like spacetime by using
the unified first law, and present the generalized Misner-Sharp mass. Our
results show that the generalized Minser-Sharp mass does exist in this
spacetime. In addition, the usual Clausius relation $\delta Q= TdS$ holds on
the apparent horizon, which implicates that the massive gravity is in a
thermodynamic equilibrium state. We find that the work density vanishes for the
generalized Vaidya solution, while it appears in the more general Vaidya-like
solution. Furthermore, the covariant generalized Minser-Sharp mass in the
$n$-dimensional de Rham-Gabadadze-Tolley massive gravity is also derived by
taking a general metric ansatz into account.Comment: 10 pages, no figure, version published in PR

- â€¦