Predrag Prester

Lovelock type gravity and small black holes in heterotic string theory

We analyze near horizon behavior of small D-dimensional 2-charge black holes by modifying tree level effective action of heterotic string with all extended Gauss-Bonnet densities. We show that there is a nontrivial and unique choice of parameters, independent of D, for which the black hole entropy in any dimension is given by 4?(nw)1/2, which is exactly the statistical entropy of 1/2-BPS states of heterotic string compactified on T9?D ? S1 with momentum n and winding w. This, in a sense, extends the results of Sen JHEP07(2005)073 to all dimensions. We also show that our Lovelock type action belongs to the more general class of actions sharing the simmilar behaviour on the AdS2 ? SD?2 near horizon geometry.

Horizon conformal entropy in Gauss–Bonnet gravity

We treat spherically symmetric black holes in Gauss–Bonnet gravity by imposing boundary conditions on fluctuating metric on the horizon. Obtained effective two-dimensional theory admits Virasoro algebra near the horizon. This enables, with the help of Cardy formula, evaluation of the number of states. Obtained results coincide with the known macroscopic expression for the entropy of black holes in Gauss–Bonnet gravity.

Dressed sliver solutions in vacuum string field theory

We consider a new class of solutions (dressed slivers) in Vacuum String Field Theory, which represent D25-branes. For each dressed sliver we introduce a deformation parameter and define a family of states which are characterized by new abelian *-subalgebras. We show that this deformation parameter can be used as a regulator: it allows us to define for each such solution a finite norm and energy density. Finally we show how to generalize these results to parallel coincident and to lower dimensional branes.

Entropy of Killing horizons from Virasoro algebra in D-dimensional extended Gauss–Bonnet gravity

We treat D-dimensional black holes with Killing horizon for extended Gauss–Bonnet gravity. We use the Carlip method and impose boundary conditions on the horizon what enables us to identify Virasoro algebra and evaluate its central charge and Hamiltonian eigenvalue. The Cardy formula allows then to calculate the number of states and thus provides for a microscopic interpretation of entropy.

On a quantum group invariant spin chain with non-local boundary conditions

We treat a one parameter family of quantum spin models, which are quantum-group invariant as well as periodic in a certain sense, using Bethe states. We analyse its ground-state properties and obtain the surprising result that its spin becomes non-zero depending on the value of the parameter. Finite-size corrections allow us to obtain the central charge which is also spin dependent. Relations to other models are mentioned.

Perturbative spectrum of the dressed sliver

We analyze the fluctuations of the dressed sliver solution found in a previous paper, hep-th/0311198, in the operator formulation of Vacuum String Field Theory. We derive the tachyon wave function and then analyze the higher level fluctuations. We show that the dressing is responsible for implementing the transversality condition on the massless vector. In order to consistently deal with the singular k=0 mode we introduce a string midpoint regulator and we show that it is possible to accommodate all the open string states among the solutions to the linearized equations of motion. We finally show how the dressing can give rise to the correct ratio between the energy density of the dressed sliver and the brane tension computed via the three-tachyons-coupling.

Curing Black Hole Singularities with Local Scale Invariance

We show that Weyl-invariant dilaton gravity provides a description of black holes without classical space-time singularities. Singularities appear due to the ill behaviour of gauge fixing conditions, one example being the gauge in which theory is classically equivalent to standard General Relativity. The main conclusions of our analysis are as follows: (1) singularities signal a phase transition from broken to unbroken phase of Weyl symmetry; (2) instead of a singularity, there is a “baby universe” or a white hole inside a black hole; (3) in the baby universe scenario, there is a critical mass after which reducing mass makes the black hole larger as viewed by outside observers; (4) if a black hole could be connected with white hole through the “singularity,” this would require breakdown of (classical) geometric description; (5) the singularity of Schwarzschild BH solution is nongeneric and so it is dangerous to rely on it in deriving general results. Our results may have important consequences for resolving issues related to information loss puzzle. Though quantum effects are still crucial and may change the proposed classical picture, a position of building quantum theory around essentially regular classical solutions normally provides a much better starting point.

Higher curvature Lagrangians, conformal symmetry and microscopic entropy of Killing horizons

We impose a certain class of boundary conditions on Killing horizon and show for Lagrangians with arbitrary curvature dependence that one can identify a Virasoro algebra with nontrivial central charge and calculable Hamiltonian eigenvalue. Entropy can then be calculated from Cardy formula.

Violation of the string hypothesis and the Heisenberg XXZ spin chain

In this paper we count the numbers of real and complex solutions to Bethe constraints in the two-particle sector of the XXZ model. We find the exact n

Small black holes in the large D limit

A bstractThe large D limit of AdS2 × SD−2 solutions in the particular higher-derivative Lovelock-type theory is analyzed. The theory and the solutions were originally considered in an attempt to effectively describe near-horizon behavior of D-dimensional spherically symmetric 2-charge small extremal black holes which in superstring theory context are assumed to correspond to configurations in S1 × T9−D compactification schemes in which fundamental string is wound around circle S1. Though in D → ∞ limit the action contains infinite number of higher-derivative terms, their contributions to equations of motion sum into simple exponential form which allows us to find explicit solutions. A simplicity of this example gives us the opportunity to study some connections between α′ and 1/D expansions. In the leading order in 1/D the relation between the string parameter α′ and the radius of the horizon rh (in the string frame) satisfies rh ∝