Gauge/gravity correspondence in accelerating universe

We discuss time-dependent backgrounds of type IIB supergravity realizing gravitation duals of gauge theories formulated in de Sitter space-time as a tool of embedding de Sitter in a supergravity. We show that only the gravitational duals to non-conformal gauge theories are sensitive to a specific value of a Hubble parameter. We consider two nontrivial solutions of this type: a gravity dual to six-dimensional (1,1) little string theory, and to a four-dimensional cascading SU(N+M)xSU(N) supersymmetric gauge theory (related to fractional D3-branes on a singular conifold according to Klebanov et al), in accelerating universe. In both cases we argue that the IR singularity of the geometry is regulated by the expansion of the gauge theory background space-time.Comment: 13 pages, harvmac, v2: reference added, v3: D3,NS5 discussion improved, PRD versio

A Non-supersymmetric Large N CFT from Type 0 String Theory

We show that type 0B theory has a classical AdS_5 x S^5 solution and argue that it is stable at the string-theory level for small enough radius. The dual 4-d conformal field theory is the infrared limit of the theory on N electric D3-branes coincident with N magnetic D3-branes. We explicitly construct this SU(N) x SU(N) gauge theory with global SO(6) symmetry and verify that the one-loop term in the beta function vanishes exactly, while the two-loop term vanishes in the large N limit. We find that this theory is related by a certain projection to the maximally supersymmetric Yang-Mills theory suggesting its large N conformal invariance to all orders in perturbation theory.Comment: 15 pages, harvmac. v2: references and a note on renormalization of Yukawa and scalar couplings added; v3: a note on orbifold interpretation added; the version to appear in JHE

Interaction of Discrete States in Two-Dimensional String Theory

We study the couplings of discrete states that appear in the string theory embedded in two dimensions, and show that they are given by the structure constants of the group of area preserving diffeomorphisms. We propose an effective action for these states, which is itself invariant under this infinite-dimensional group.Comment: 12 page

Evaporation of Schwarzschild Black Holes in Matrix Theory

Recently, in collaboration with Susskind, we proposed a model of Schwarzschild black holes in Matrix theory. A large Schwarzschild black hole is described by a metastable bound state of a large number of D0-branes which are held together by a background, whose structure has so far been understood only in 8 and 11 dimensions. The Hawking radiation proceeds by emission of small clusters of D0-branes. We estimate the Hawking rate in the Matrix theory model of Schwarzschild black holes and find agreement with the semiclassical rate up to an undetermined numerical coefficient of order 1.Comment: 9 pages, harvma

Absorption by Threebranes and the AdS/CFT Correspondence

In the first part of this talk I discuss two somewhat different supergravity approaches to calculating correlation functions in strongly coupled Yang-Mills theory. The older approach relates two-point functions to cross-sections for absorption of certain incident quanta by threebranes. In this approach the normalization of operators corresponding to the incident particles is fixed unambiguously by the D3-brane DBI action. By calculating absorption cross-sections of all partial waves of the dilaton we find corresponding two-point functions at strong `t Hooft coupling and show that they are identical to the weak coupling results. The newer approach to correlation functions relates them to boundary conditions in AdS space. Using this method we show that for a certain range of negative mass-squared there are two possible operator dimensions corresponding to a given scalar field in AdS, and indicate how to calculate correlation functions for either of these choices. In the second part of the talk I discuss an example of AdS/CFT duality which arises in the context of type 0 string theory. The CFT on N coincident electric and magnetic D3-branes is argued to be stable for sufficiently weak `t Hooft coupling. It is suggested that its transition to instability at a critical coupling is related to singularity of planar diagrams.Comment: 14 pages, LaTeX; Talk at Strings '99, Potsdam, German

Entropy and Temperature of Black 3-Branes

We consider slightly non-extremal black 3-branes of type IIB supergravity and show that their Bekenstein-Hawking entropy agrees, up to a mysterious factor, with an entropy derived by counting non-BPS excitations of the Dirichlet 3-brane. These excitations are described in terms of the statistical mechanics of a 3+1 dimensional gas of massless open string states. This is essentially the classic problem of blackbody radiation. The blackbody temperature is related to the temperature of the Hawking radiation. We also construct a solution of type IIB supergravity describing a 3-brane with a finite density of longitudinal momentum. For extremal momentum-carrying 3-branes the horizon area vanishes. This is in agreement with the fact that the BPS entropy of the momentum-carrying Dirichlet 3-branes is not an extensive quantity.Comment: 10 pages, LaTeX, minor revisions. v3: version that appeared in PR