15772562
Increase of black hole entropy in higher curvature gravity.
We examine the Zeroth Law and the Second Law of black hole thermodynamics within the context of effective gravitational actions including higher curvature interactions. We show that entropy can never decrease for quasi-stationary processes in which a black hole accretes positive energy matter, independent of the details of the gravitational action. Within a class of higher curvature theories where the Lagrangian consists of a polynomial in the Ricci scalar, we use a conformally equivalent theory to establish that stationary black hole solutions with a Killing horizon satisfy the Zeroth Law, and that the Second Law holds in general for any dynamical process. We also introduce a new method for establishing the Second Law based on a generalization of the area theorem, which may prove useful for a wider class of Lagrangians. Finally, we show how one can infer the form of the black hole entropy, at least for the Ricci polynomial theories, by integrating the changes of mass and angular momentum in a quasistationary accretion process.
122217474
ISOTROPY OF THE ZERO-POINT FIELD IN A UNIFORMLY ACCELERATED FRAME
The angular dependence of the zero-point field energy of the massless scalar field in a uniformly accelerated frame is computed. The spectrum seen by the observer in the accelerated frame is shown to be isotropic and thus to be thermal.
18393402
Stability of the GRS model
Abstract We discuss the compatibility between the weaker energy condition and the stability of Gregory, Rubakov and Sibiryakov (GRS) model. Because the GRS spacetime violates the weak energy condition, it may cause the instability. In the GRS model, the four-dimensional gravity can be described by the massive KK modes with the resonance. Hence, instead of considering the weaker energy condition, we require for the stability of this model: no tachyon and no ghost condition for graviton modes ( h μν ). No tachyonic condition ( m 2 h ⩾0) is satisfied because the lowest state m h =0 is supersymmetric vacuum state. Further, no ghost state condition is achieved if one requires some relations for the matter source: 2 T 55 = T μ μ =3( T 22 + T 33 ). It turns out that, although the GRS spacetime does not satisfy the weaker energy condition, it is stable against small perturbation.
14314442
U(1) gauge field of the Kaluza-Klein theory in the presence of branes
We investigate the zero mode dimensional reduction of the Kaluza-Klein unifications in the presence of a single brane in the infinite extra dimension. We treat the brane as fixed, not a dynamical object, and do not require the orbifold symmetry. It seems that, contrary to the standard Kaluza-Klein models, the 4D effective action is no longer invariant under the U(1) gauge transformations due to the explicit breaking of isometries in the extra dimension by the brane. Surprisingly, however, the linearized perturbation analysis around the RS vacuum shows that the Kaluza-Klein gauge field does possess the U(1) gauge symmetry at the linear level. In addition, the graviscalar also behaves differently from the 4D point of view. Some physical implications of our results are also discussed.
117821718
Classical stability of lower dimensional black strings / branes
It is shown that BTZ black strings in four dimensions are stable under small perturbations regardless of the horizon size. Such stable feature seems to be common for several known black strings or branes in dimensions lower than five.
32962928
Near-horizon conformal symmetry and black hole entropy in any dimension
Recently, Carlip proposed a derivation of the entropy of the two-dimensional dilatonic black hole by investigating the Virasoro algebra associated with a newly introduced near-horizon conformal symmetry. We point out not only that the algebra of these conformal transformations is not well defined on the horizon, but also that the correct use of the eigenvalue of the operator ${L}_{0}$ yields vanishing entropy. It has been shown that these problems can be resolved by choosing a different basis of the conformal transformations which is regular even at the horizon. We also show the generalization of Carlip's derivation to any higher dimensional case in pure Einstein gravity. The entropy obtained is proportional to the area of the event horizon, but it also depends linearly on the product of the surface gravity and the parameter length of a horizon segment in consideration. We finally point out that this derivation of black hole entropy is quite different from the ones proposed so far, and several features of this method and some open issues are also discussed.
6673120
Lightest Higgs boson mass in the minimal supersymmetric standard model with four generations.
We study a bound on the lightest Higgs boson mass in the minimal supersymmetric standard model (MSSM) with four generations by solving the one-loop renormalization group equations. We show how the bound depends on the fourth generation fermion masses as well as the top quark mass. We also briefly compare the bound with the one in the MSSM with three generations. {copyright} {ital 1996 The American Physical Society.}