Topics in stringy cosmology

Doctoral Thesis


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University of Cape Town

This thesis is composed of two distinct research topics. The first topic concerns Randall-Sundrum cosmological models, in particular their isotropization properties at early times. We first study the state space of inflationary braneworld models with exponential potential and identify the past and future attractors within the homogeneous state space. Our main result is that the isotropic high energy BDL model is the generic past attractor in the state space of FLRW braneworld models. In the state space of Bianchi I models both the BDL model and the inflationary anisotropic Kasner model are past attractors. We then address the question of isotropization using a different approach by studying the evolution of general inhomogeneous and anisotropic perturbations around the spatially flat FLRW braneworld background for three different energy regimes. Here we find that for the high energy braneworld background, the physically relevant anisotropic, inhomogeneous perturbations decay when approaching the initial singularity. We confirm the standard results for thelow energy limit: as in General Relativity, the anisotropy here grows in the past. We conclude that the initial singularity appears to be generically homogeneous and isotropic in the braneworld context.

Includes bibliographical references.