Black hole evaporation and higher-derivative gravity

We examine the role which higher-derivative gravity interactions may play in black hole evaporation. The thermodynamic properties of black holes in Lovelock gravity are described. In certain cases, the specific heat of a black hole becomes positive at a small mass. This results in an infinite lifetime for the black hole (and also allows it to achieve stable equilibrium with a thermal environment). Thus no conflict with unitary time evolution would arise in such theories.This essay received the fourth award from the Gravity Research Foundation for the year 1988.-Ed.     

Magnetic monopoles from a hidden magnetic symmetry

It is proposed that Magnetic Monopoles (MMs) could originate from a new U(1)_M symmetry. Such an abelian symmetry is assumed to be related to the conservation of a magnetic number M. This number is associated with massive MMs corresponding to an expected high scale breaking of the magnetic symmetry. The involved scales are approached and the properties of such MMs are investigated including their detection prospects.     

Einstein's gravity from a first order lagrangian in an embedding space

We formulate a first order action principle in a higher dimensional space M_N in which we embed spacetime. The action I is essentially an “area” of a four-dimensional spacetime V₄ weighted with a matter density ω in M_N. For a suitably chosen ω we obtain on V₄ a set of worldlines. It is shown that these worldlines are geodesics of V₄, provided that V₄ is a solution to our variational procedure. Then it follows that our spacetime satisfies the Einstein equations for dust - apart from an additional term with zero covariant divergence. (This extra term was shown in a previous paper to be exactly zero at least in the case of the cosmological dust model.) Thus we establish a remarkable connection of the extrinsic spacetime theory with the intrinsic general relativity. This step appears to be important for quantum gravity.     

Black hole state counting in loop quantum gravity: a number-theoretical approach

We give an efficient method, combining number-theoretic and combinatorial ideas, to exactly compute black hole entropy in the framework of loop quantum gravity. Along the way we provide a complete characterization of the relevant sector of the spectrum of the area operator, including degeneracies, and explicitly determine the number of solutions to the projection constraint. We use a computer implementation of the proposed algorithm to confirm and extend previous results on the detailed structure of the black hole degeneracy spectrum.     

Black hole remnants due to GUP or quantum gravity?

Based on the micro-black hole gedanken experiment as well as on general considerations of quantum mechanics and gravity the generalized uncertainty principle (GUP) is analyzed by using the running Newton constant. The result is used to decide between the GUP and quantum gravitational effects as a possible mechanism leading to the black hole remnants of about Planck mass.     

Black hole radiance, short distances, and TeV gravity

Using a derivation of black hole radiance in terms of two-point functions one can provide a quantitative estimate of the contribution of short distances to the spectrum. Thermality is preserved for black holes with kappalp<1. However, deviations from the Planckian spectrum can be found for mini black holes in TeV gravity scenarios, even before reaching the Planck phase.     

Black hole physics from Liouville theory

In a previous paper it was shown that the quantum consistency conditions for the dilaton-gravity theory of Callan et al., imply that the cosmological constant term undergoes a dilaton dependent renormalization, in such a manner that the theory can be written as a Liouville-like theory. In this paper we discuss the physical interpretation of the solutions of this theory. In particular we demonstrate explicitly how quantum corrections tame the black hole singularity. Finally we discuss Hawking radiation and find that it is asymptotically constant, but the value of the constant depends on an undetermined parameter.     

Notes on the hidden conformal symmetry in the near horizon geometry of the Kerr black hole

Toward the Kerr/CFT correspondence for the generic non-extremal Kerr black hole, the analysis of scattering amplitudes by near extremal Kerr provides a clue. This pursuit reveals a hidden conformal symmetry in the low frequency wave equation for a scalar field in a certain spacetime region referred to as the near region. For extremal case, the near region is expected to be the near horizon region in which the correspondence via the asymptotic symmetry is studied. We investigate the hidden conformal symmetry in the near horizon limit and consider the relation between the hidden conformal symmetry and the asymptotic symmetry in the near horizon limit. By using an appropriate definition of the quasi-local charge, we obtain the deviation of the entropy from the extremality.     

Anti-parity-time symmetry hidden in a damping linear resonator

Phase transition from the over-damping to under-damping states is a ubiquitous phenomenon in physical systems. However, what kind of symmetry is broken associated with this phase transition remains unclear. Here, we discover that this phase transition is determined by an anti-parity-time(anti-PT) symmetry hidden in a single damping linear resonator, which is significantly different from the conventional anti-PT-symmetric systems with two or more modes. We show that the breaking of the anti-PT sy...     

Black hole thermodynamics from a possible model for internal structure

Treating a black hole as a relativistic gas of microblack holes (planckions) which have fermionic character, expressions for some thermodynamic quantities are obtained. These have the same structure as those obtained by Hawking by other considerations.     

Island of stability for consistent deformations of Einstein's gravity

We construct deformations of general relativity that are consistent and phenomenologically viable, since they respect, in particular, cosmological backgrounds. These deformations have unique symmetries in accordance with their Minkowski cousins (Fierz-Pauli theory for massive gravitons) and incorporate a background curvature induced self-stabilizing mechanism. Self-stabilization is essential in order to guarantee hyperbolic evolution in and unitarity of the covariantized theory, as well as the deformation's uniqueness. We show that the deformation's parameter space contains islands of absolute stability that are persistent through the entire cosmic evolution.     

Quasi-normal modes of extremal black holes from hidden conformal symmetry

In this Letter, we construct the quasi-normal modes of three-dimensional extremal black holes in an algebraic way. We show that the infinite towers of the quasi-normal modes of scalar, vector and tensor could be constructed as the descendents of the highest weight modes. Our investigation shows that the hidden conformal symmetry suggested in Chen et al. (2010) [5] is an intrinsic property of the extremal black hole. Moreover, we notice that we need to fix the freedom in defining the local vector fields and find the right hidden conformal symmetry to obtain the physical quasi-normal modes.     

平面对称黑洞的统计熵

避开求解各种粒子波动方程的困难,直接应用量子统计的方法,计算平面对称黑面背景下玻色场与费米场的配分函数,得到黑面熵的积分表达式.然后应用改进的brickwall方法膜模型,计算黑面视界所对应的统计熵.在所得结果中当所取的积分下限和上限都趋于视界上时,可得到黑面熵与相应黑面视界面积成正比的关系,不存在原brickwall方法中的舍去项与对数发散项.整个计算过程,物理图像清楚,计算简单,为研究黑洞熵提供了一条简捷的新途径 关键词： 量子统计 膜模型 黑面熵     

Black hole thermodynamics from Euclidean horizon constraints

To explain black hole thermodynamics in quantum gravity, one must introduce constraints to ensure that a black hole is actually present. I show that for a large class of black holes, such "horizon constraints" allow the use of conformal field theory techniques to compute the density of states, reproducing the Bekenstein-Hawking entropy in a nearly model-independent manner. One standard string theory approach to black hole entropy arises as a special case, lending support to the claim that the mechanism may be "universal." I argue that the relevant degrees of freedom are Goldstone-boson-like excitations arising from the weak breaking of symmetry by the constraints.