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

On effective action of string theory flux compactifications

We discuss four dimensional effective actions of string theory flux compactifications. These effective actions describe four dimensional gravity coupled to overall Kahler modulus of the compactification manifold. We demonstrate the agreement between ten dimensional equations of motion of supergravity with localized branes, and equations of motion derived from the effective action. The agreement is lost however if one evaluates the full effective action on the equations of motion for a subset of the supergravity modes, provided these modes depend on-shell on the Kahler modulus.Comment: 25 pages; v2: refs adde

Gauge/string correspondence in curved space

We discuss Gubser-Klebanov-Polyakov proposal for the gauge/string theory correspondence for gauge theories in curved space. Specifically, we consider Klebanov-Tseytlin cascading gauge theory compactified on S^3. We explain regime when this gauge theory is a small deformation of the superconformal N=1 gauge theory on the world volume of regular D3-branes at the tip of the conifold. We study closed string states on the leading Regge trajectory in this background, and attempt to identify the dual gauge theory twist two operators.Comment: 26 pages, v2: refs adde

Viscosity Bound and Causality in Superfluid Plasma

It was argued by Brigante et.al that the lower bound on the ratio of the shear viscosity to the entropy density in strongly coupled plasma is translated into microcausality violation in the dual gravitational description. Since transport properties of the system characterize its infrared dynamics, while the causality of the theory is determined by its ultraviolet behavior, the viscosity bound/microcausality link should not be applicable to theories that undergo low temperature phase transitions. We present an explicit model of AdS/CFT correspondence that confirms this fact.Comment: 27 pages, 5 figures. References added, typos fixe

Transport coefficients, membrane couplings and universality at extremality

We present an efficient method for computing the zero frequency limit of transport coefficients in strongly coupled field theories described holographically by higher derivative gravity theories. Hydrodynamic parameters such as shear viscosity and conductivity can be obtained by computing residues of poles of the off-shell lagrangian density. We clarify in which sense these coefficients can be thought of as effective couplings at the horizon, and present analytic, Wald-like formulae for the shear viscosity and conductivity in a large class of general higher derivative lagrangians. We show how to apply our methods to systems at zero temperature but finite chemical potential. Our results imply that such theories satisfy $\eta/s=1/4\pi$ universally in the Einstein-Maxwell sector. Likewise, the zero frequency limit of the real part of the conductivity for such systems is shown to be universally zero, and we conjecture that higher derivative corrections in this sector do not modify this result to all orders in perturbation theory.Comment: 29 pages, v2: Small text changes for clarity, typos correcte

Comments on supergravity dual of pure N=1 Super Yang Mills theory with unbroken chiral symmetry

Maldacena and Nunez [hep-th/0008001] identified a gravity solution describing pure N=1 Yang-Mills (YM) in the IR. Their (smooth) supergravity solution exhibits confinement and the U(1)_R chiral symmetry breaking of the dual YM theory, while the singular solution corresponds to the gauge theory phase with unbroken U(1)_R chiral symmetry. In this paper we discuss supersymmetric type IIB compactifications on resolved conifolds with torsion. We rederive singular background of [hep-th/0008001] directly from the supersymmetry conditions. This solution is the relevant starting point to study non-BPS backgrounds dual to the high temperature phase of pure YM. We construct the simplest black hole solution in this background. We argue that it has a regular Schwarzschild horizon and provides a resolution of the IR singularity of the chirally symmetric extremal solution as suggested in [hep-th/0011146].Comment: 34 pages, LaTeX, v2: references added, v3: section 2 reduced, minor clarifications, to be published in PR

Hydrodynamics of fundamental matter

First and second order transport coefficients are calculated for the strongly coupled N=4 SYM plasma coupled to massless fundamental matter in the Veneziano limit. The results, including among others the value of the bulk viscosity and some relaxation times, are presented at next-to-leading order in the flavor contribution. The bulk viscosity is found to saturate Buchel's bound. This result is also captured by an effective single-scalar five-dimensional holographic dual in the Chamblin-Reall class and it is suggested to hold, in the limit of small deformations, for generic plasmas with gravity duals, whenever the leading conformality breaking effects are driven by marginally (ir)relevant operators. This proposal is then extended to other relations for hydrodynamic coefficients, which are conjectured to be universal for every non-conformal plasma with a dual Chamblin-Reall-like description. Our analysis extends to any strongly coupled gauge theory describing the low energy dynamics of Nc>>1 D3-branes at the tip of a generic Calabi-Yau cone. The fundamental fields are added by means of 1<<Nf<<Nc homogeneously smeared D7-branes.Comment: 24 pages. V2: Important improvements in the discussion of the results in section 1. References adde