String Gas Cosmology

TL;DR

String Gas Cosmology explores how string gases influence the evolution of extra dimensions and dark matter, proposing a late-time stabilization mechanism and alternative dark matter models within string theory.

Contribution

The paper provides a comprehensive review of string gas cosmology, including derivations from string theory, and introduces a quantum stabilization mechanism for extra dimensions.

Findings

Quantum string gases can stabilize extra dimensions at late times.

String gases offer alternative frameworks for dark matter beyond $$CDM.

Classical gas dynamics require fine-tuning and are less reliable.

Abstract

We present a critical review and summary of String Gas Cosmology. We include a pedagogical derivation of the effective action starting from string theory, emphasizing the necessary approximations that must be invoked. Working in the effective theory, we demonstrate that at late-times it is not possible to stabilize the extra dimensions by a gas of massive string winding modes. We then consider additional string gases that contain so-called enhanced symmetry states. These string gases are very heavy initially, but drive the moduli to locations that minimize the energy and pressure of the gas. We consider both classical and quantum gas dynamics, where in the former the validity of the theory is questionable and some fine-tuning is required, but in the latter we find a consistent and promising stabilization mechanism that is valid at late-times. In addition, we find that string gases provide a framework to explore dark matter, presenting alternatives to $\Lambda$CDM as recently considered by Gubser and Peebles. We also discuss quantum trapping with string gases as a method for including dynamics on the string landscape.