Extracting the bulk metric from boundary information in asymptotically AdS spacetimes

We use geodesic probes to recover the entire bulk metric in certain asymptotically AdS spacetimes. Given a spectrum of null geodesic endpoints on the boundary, we describe two remarkably simple methods for recovering the bulk information. After examining the issues which affect their application in practice, we highlight a significant advantage one has over the other from a computational point of view, and give some illustrative examples. We go on to consider spacetimes where the methods cannot be used to recover the complete bulk metric, and demonstrate how much information can be recovered in these cases.Comment: 33 pages, 11 figures; v2 references adde

Normal mode analysis for scalar fields in BTZ black hole background

We analyze the possibility of inequivalent boundary conditions for a scalar field propagating in the BTZ black hole space-time. We find that for certain ranges of the black hole parameters, the Klein-Gordon operator admits a one-parameter family of self-adjoint extensions. For this range, the BTZ space-time is not quantum mechanically complete. We suggest a physically motivated method for determining the spectra of the Klein-Gordon operator.Comment: 6 pages, no figure, late

Non-extremal Stringy Black Hole

We construct a four-dimensional BPS saturated heterotic string solution from the Taub-NUT solution. It is a non-extremal black hole solution since its Euler number is non-zero. We evaluate its black hole entropy semiclassically. We discuss the relation between the black hole entropy and the degeneracy of string states. The entropy of our string solution can be understood as the microscopic entropy which counts the elementary string states without any complications.Comment: 18 pages, Late

Dimensional Reduction in Non-Supersymmetric Theories

It is shown that regularisation by dimensional reduction is a viable alternative to dimensional regularisation in non-supersymmetric theories.Comment: 13 pages, phyzzx, LTH 32

B^F Theory and Flat Spacetimes

We propose a reduced constrained Hamiltonian formalism for the exactly soluble $B \wedge F$ theory of flat connections and closed two-forms over manifolds with topology $\Sigma^3 \times (0,1)$. The reduced phase space variables are the holonomies of a flat connection for loops which form a basis of the first homotopy group $\pi_1(\Sigma^3)$, and elements of the second cohomology group of $\Sigma^3$ with value in the Lie algebra $L(G)$. When $G=SO(3,1)$, and if the two-form can be expressed as $B= e\wedge e$, for some vierbein field $e$, then the variables represent a flat spacetime. This is not always possible: We show that the solutions of the theory generally represent spacetimes with ``global torsion''. We describe the dynamical evolution of spacetimes with and without global torsion, and classify the flat spacetimes which admit a locally homogeneous foliation, following Thurston's classification of geometric structures.Comment: 21 pp., Mexico Preprint ICN-UNAM-93-1

Strings, T-duality breaking, and nonlocality without the shortest distance

T-duality of string theory suggests nonlocality manifested as the shortest possible distance. As an alternative, we suggest a nonlocal formulation of string theory that breaks T-duality at the fundamental level and does not require the shortest possible distance. Instead, the string has an objective shape in spacetime at all length scales, but different parts of the string interact in a nonlocal Bohmian manner.Comment: 7 pages, revised, to appear in Eur. Phys. J.

Black Hole Entropy from a Highly Excited Elementary String

Suggested correspondence between a black hole and a highly excited elementary string is explored. Black hole entropy is calculated by computing the density of states for an open excited string. We identify the square root of oscillator number of the excited string with Rindler energy of black hole to obtain an entropy formula which, not only agrees at the leading order with the Bekenstein-Hawking entropy, but also reproduces the logarithmic correction obtained for black hole entropy in the quantum geometry framework. This provides an additional supporting evidence for correspondence between black holes and strings.Comment: revtex, 4 page

A lattice formulation of chiral gauge theories

We present a method for implementing gauge theories of chiral fermions on the lattice.Comment: 3 pages LaTeX, espcrc2 style file. Talk presented at LATTICE96(chiral gauge

Hawking radiation of nonsingular black holes in two dimensions

In this letter we study the process of Hawking radiation of a black hole assuming the existence of a limiting physical curvature scale. The particular model is constructed using the Limiting Curvature Hypothesis (LCH) and in the context of two-dimensional dilaton gravity. The black hole solution exhibits properties of the standard Schwarzschild solution at large values of the radial coordinate. However, near the center, the black hole is nonsingular and the metric becomes that of de Sitter spacetime. The Hawking temperature is calculated using the method of complex paths. We find that such black holes radiate eternally and never completely evaporate. The final state is an eternally radiating relic, near the fundamental scale, which should make a viable dark matter candidate. We briefly comment on the black hole information loss problem and the production of such black holes in collider experiments.Comment: 8 pages, 4 figures; minor revisions; references added; version to appear in JHE

Holographic Domains of Anti-de Sitter Space

An AdS_4 brane embedded in AdS_5 exhibits the novel feature that a four-dimensional graviton is localized near the brane, but the majority of the infinite bulk away from the brane where the warp factor diverges does not see four-dimensional gravity. A naive application of the holographic principle from the point of view of the four-dimensional observer would lead to a paradox; a global holographic mapping would require infinite entropy density. In this paper, we show that this paradox is resolved by the proper covariant formulation of the holographic principle. This is the first explicit example of a time-independent metric for which the spacelike formulation of the holographic principle is manifestly inadequate. Further confirmation of the correctness of this approach is that light-rays leaving the brane intersect at the location where we expect four-dimensional gravity to no longer dominate. We also present a simple method of locating CFT excitations dual to a particle in the bulk. We find that the holographic image on the brane moves off to infinity precisely when the particle exits the brane's holographic domain. Our analysis yields an improved understanding of the physics of the AdS_4/AdS_5 model.Comment: 29 pages, 6 figure