Holographic cosmology and string theory

Abstract

Inflation is part of the current standard model of cosmology and describes a period of rapid expansion in the early universe. Besides its success in solving many of the problems with the big bang cosmology and fitting the CMBR data, inflation is far from being a complete description: it suffers from trans-Planckian issues, does not solve the initial singularity problem, and needs a huge fine-tuning to explain the observed cosmological constant. Since inflation is highly UV sensitive, we expect it can be derived as an effective theory from a quantum theory of gravity, like string theory. Along with string theory models for inflation, other approaches use the gauge/gravity duality applied to cosmology to describe a strongly-coupled gravity phase in the early cosmology in terms of a $3$-dimensional perturbative field theory, in a framework called \emph{holographic cosmology}. In this project, we want to explore different applications of the gauge/gravity duality and string theory methods to cosmology, namely: to further define a phenomenological approach, and find a good top-down approach to holographic cosmology, to describe reheating, a transition from the nongeometric phase of gravity to the usual radiation-dominated era, and in the string/brane gas cosmology model. (AU)