On the origin of thermal string gas

We investigate decaying D-branes as the origin of the thermal string gas of string gas cosmology. We consider initial configurations of low-dimensional branes and argue that they can time evolve to thermal string gas. We find that there is a range in the weak string coupling and fast brane decay time regimes, where the initial configuration could drive the evolution of the dilaton to values, where exactly three spacelike directions grow large.Comment: 16 pages, 4 figures, v2: references adde

Gravity duals for logarithmic conformal field theories

Logarithmic conformal field theories with vanishing central charge describe systems with quenched disorder, percolation or dilute self-avoiding polymers. In these theories the energy momentum tensor acquires a logarithmic partner. In this talk we address the construction of possible gravity duals for these logarithmic conformal field theories and present two viable candidates for such duals, namely theories of massive gravity in three dimensions at a chiral point.Comment: 15 pages, 1 figure, invited plenary talk at the First Mediterranean Conference on Classical and Quantum Gravity, v2: published version, corrected typo in left eq. (5

Holographic Hydrodynamics with a Chemical Potential

We consider five-dimensional gravity coupled to a negative cosmological constant and a single U(1) gauge field, including a general set of four-derivative interactions. In this framework, we construct charged planar AdS black hole solutions perturbatively and consider the thermal and hydrodynamic properties of the plasma in the dual CFT. In particular, we calculate the ratio of shear viscosity to entropy density and argue that the violation of the KSS bound is enhanced in the presence of a chemical potential. We also compute the electrical conductivity and comment on various conjectured bounds related to this coefficient.Comment: v2: comparison to supergravity lagrangian added, references added, typos fixe

Quantum Gravity, Field Theory and Signatures of Noncommutative Spacetime

A pedagogical introduction to some of the main ideas and results of field theories on quantized spacetimes is presented, with emphasis on what such field theories may teach us about the problem of quantizing gravity. We examine to what extent noncommutative gauge theories may be regarded as gauge theories of gravity. UV/IR mixing is explained in detail and we describe its relations to renormalization, to gravitational dynamics, and to deformed dispersion relations in models of quantum spacetime of interest in string theory and in doubly special relativity. We also discuss some potential experimental probes of spacetime noncommutativity.Comment: 26 pages, 4 figures; v2: comments and references added; v3: typos corrected, clarifying comments and references added; Based on Plenary Lecture delivered at the XXIX Encontro Nacional de Fisica de Particulas e Campos, Sao Lourenco, Brasil, September 22-26, 2008; Final version to be published in General Relativity and Gravitatio