Lectures on string/brane cosmology

TL;DR

This paper surveys the landscape of string/brane cosmology, examining how string theory can address foundational cosmological questions such as the origin of inflation, the big bang, and the nature of dark energy. It emphasizes a spectrum of approaches, from D-brane inflation and tachyon condensation to pre-big-bang, S-brane, and ekpyrotic/cyclic scenarios, highlighting both their concrete string-theoretic structure and their conceptual challenges. The discussion underscores moduli stabilization, singularity resolution, and the quest for observable signatures (e.g., cosmic strings, tensor modes, and trans-Planckian effects) as critical tests for any string-derived cosmology. Overall, the work identifies three particularly promising frameworks—D-brane inflation, pre big-bang, and ekpyrotic/cyclic models—while acknowledging that a fully realistic, top-down string cosmology remains an open, active area of research.

Abstract

An overview is presented of some cosmological aspects of string theory. Recent developments are emphasised, especially the attempts to derive inflation or alternatives to inflation from the dynamics of branes in string theory. Time dependent backgrounds with potential cosmological implications, such as those provided by negative tension branes and S-branes and the rolling string tachyon are also discussed.