Quantum Corrections to Black Hole Entropy in String Theory

The one-loop contribution to the entropy of a black hole from field modes near the horizon is computed in string theory. It is modular invariant and ultraviolet finite. There is an infrared divergence that signifies an instability near the event horizon of the black hole. It is due to the exponential growth of the density of states and the associated Hagedorn transition characteristic of string theory. It is argued that this divergence is indicative of a tree level contribution, and the Bekenstein-Hawking-Gibbons formula for the entropy should be understood in terms of string states stuck near the horizon.Comment: 15 pages, harvmac, replaced with version published in Phys. Letts.

On Condensation of Closed-string Tachyons

An F-theory dual of a nonsupersymmetric orientifold is considered. It is argued that the condensation of both open and closed string tachyons in the orientifold corresponds to the annihilation of branes and anti-branes in the F-theory dual. The end-point of tachyon condensation is thus expected to be the vacuum of Type-IIB superstring. Some speculations are presented about the F-theory dual of the bosonic string and tachyon condensation thereof.Comment: 16 pages, 2 figures, harvmac(b

Structural Vulnerabilities and Currency Crises

This paper examines the role of structural factors - governance and rule of law, corporate sector governance (creditor rights and shareholder rights), corporate financing structure - as well as macroeconomic variables in currency crises. Using a technique known as a binary recursive tree allows for interactions between the various explanatory variables. It is found that structural vulnerabilities play an important role in the occurrence of "deep" currency crises (those with a real GDP growth decline of at least 3 percentage points) and that there are complex interactions between these structural vulnerabilities and macroeconomic imbalances. Copyright 2003, International Monetary Fund

Exchange Rate Regimes: Choices and Consequences (A. R. Ghosh ? A.-M. Gulde ? H. C. Wolf)

exchange rate regimes, economic growth, currency crises

Exact Counting of Black Hole Microstates

The exact entropy of two-charge supersymmetric black holes in N=4 string theories is computed to all orders using Wald's formula and the supersymmetric attractor equations with an effective action that includes the relevant higher curvature terms. Classically, these black holes have zero area but the attractor equations are still applicable at the quantum level. The quantum corrected macroscopic entropy agrees precisely with the microscopic counting for an infinite tower of fundamental string states to all orders in an asymptotic expansion.Comment: 4 pages, latex, minor change