17135495
Hawking radiation of an apparent horizon in a FRW universe
Hawking radiation is an important quantum phenomenon of a black hole, which is closely related to the existence of an event horizon of a black hole. The cosmological event horizon of de Sitter space is also of Hawking radiation with a thermal spectrum. By use of the tunneling approach, we show that there is indeed a Hawking radiation with temperature, T = 1/2 pi(r) over tilde (A), for a locally defined apparent horizon of a Friedmann-Robertson-Walker universe with any spatial curvature, where (r) over tilde (A) is the apparent horizon radius. Thus we fill in the gap existing in the literature investigating the relation between the first law of thermodynamics and Friedmann equations; there the apparent horizon is assumed to have such a temperature without any proof. In addition, we stress the implication of the Hawking temperature associated with the apparent horizon.
15468224
Conformal symmetry for rotating D-branes
Abstract We apply the Kerr/CFT correspondence to the rotating black p -brane solutions. These solutions give the simplest examples from string theory point of view. Their near horizon geometries have structures of AdS, even though black p -brane solutions do not have AdS-like structures in the non-rotating case. The microscopic entropy which can be calculated via the Cardy formula exactly agrees with Bekenstein–Hawking entropy.
118832955
Generalized Vaidya spacetime in Lovelock gravity and thermodynamics on the apparent horizon
We present a kind of generalized Vaidya solutions in a generic Lovelock gravity. This solution generalizes the simple case in Gauss-Bonnet gravity reported recently by some authors. We study the thermodynamics of apparent horizon in this generalized Vaidya spacetime. Treating those terms except for the Einstein tensor as an effective energy-momentum tensor in the gravitational field equations, and using the unified first law in Einstein gravity theory, we obtain an entropy expression for the apparent horizon. We also obtain an energy expression of this spacetime, which coincides with the generalized Misner-Sharp energy proposed by Maeda and Nozawa in Lovelock gravity.
119166729
Generalized Misner-Sharp energy in f (R) gravity
We study generalized Misner-Sharp energy in f(R) gravity in a spherically symmetric space-time. We find that unlike the cases of Einstein gravity and Gauss-Bonnet gravity, the existence of the generalized Misner-Sharp energy depends on a constraint condition in the f(R) gravity. When the constraint condition is satisfied, one can define a generalized Misner-Sharp energy, but it cannot always be written in an explicit quasilocal form. However, such a form can be obtained in a Friedmann-Robertson-Walker universe and for static spherically symmetric solutions with constant scalar curvature. In the Friedmann-Robertson-Walker universe, the generalized Misner-Sharp energy is nothing but the total matter energy inside a sphere with radius r, which acts as the boundary of a finite region under consideration. The case of scalar-tensor gravity is also briefly discussed.
13904918
Entropy function and the attractor mechanism for spherically symmetric extremal black holes
In this paper we elaborate on the relation between the entropy formula of Wald and the "entropy function" method proposed by Sen. For spherically symmetric extremal black holes, it is shown that the expression of extremal black hole entropy given by Sen can be derived from the general entropy definition of Wald, without the help of the treatment of rescaling the AdS(2) part of the near horizon geometry of extremal black holes. In our procedure, we only require that the surface gravity approaches to zero, and it is easy to understand the Legendre transformation of f, the integration of Lagrangian density on the horizon, with respect to the electric charges. Since the Noether charge form can be defined in an "off-shell" form, we define a corresponding entropy function, with which one can discuss the attractor mechanism for extremal black holes with scalar fields.
118388644
Generalized formalism in gauge-invariant gravitational perturbations
By the use of the gauge-invariant variables proposed by Kodama and Ishibashi, we obtain the most general perturbation equations in the (m + n)-dimensional spacetime with a warped product metric. These equations do not depend on the spectral expansions of the Laplace-type operators on the n-dimensional Einstein manifold. These equations enable us to have a complete gauge-invariant perturbation theory and a well-defined spectral expansion for all modes, and the gauge invariance is kept for each mode. By studying perturbations of some projections of Weyl tensor in the case of m = 2, we define three Teukolsky-like gauge-invariant variables and obtain the perturbation equations of these variables by considering the perturbations of the Penrose wave equations in the (2 + n)-dimensional Einstein spectime. In particular, we find the relations between the Teukolsky-like gauge-invariant variables and the Kodama-Ishibashi gauge-invariant variables. These relations imply that the Kodama-Ishibashi gauge-invariant variables all come from the perturbations of the Weyl tensor of the spacetime.
119114673
Charmonium States in QCD-Inspired Quark Potential Model Using Gaussian Expansion Method
We investigate the mass spectrum and electromagnetic processes of charmonium system with the nonperturbative treatment for the spin-dependent potentials, comparing the pure scalar and scalar-vector mixing linear confining potentials. It is revealed that the scalar-vector mixing confinement would be important for reproducing the mass spectrum and decay widths, and therein the vector component is predicted to be around 22 %. With the state wave functions obtained via the full-potential Hamiltonian, the long-standing discrepancy in M1 radiative transitions of J/ψ and ψ′ are alleviated. This work also provides an inspection and suggestion for the possible cc̄ states among the copious higher charmonium-like states. Particularly, the newly observed X(4160) and X(4350) are found in the charmonium family mass spectrum as M(21D2) = 4164.9 MeV and M(33P2) = 4352.4 MeV, which strongly favor the JPC = 2−+, 2++ assignments respectively. The corresponding radiative transitions, leptonic and two-photon decay widths have been also predicted theoretically for the further experimental search.