Open Strings on D-Branes and Hagedorn Regime in String Gas Cosmology

TL;DR

This paper explores early universe evolution in string gas cosmology with open strings on D-branes, highlighting thermodynamic differences from closed strings and discussing stability challenges and large radius regimes.

Contribution

It provides a detailed analysis of open string thermodynamics on D-branes and examines the implications for early universe cosmology, including stability issues and large radius behavior.

Findings

Open strings on D-branes exhibit distinct Hagedorn thermodynamics.

Thermal equilibrium and Jeans instability are difficult to reconcile in this setup.

Large radius regimes show specific characteristics influenced by open string dynamics.

Abstract

We consider early time cosmic evolution in string gas cosmology dominated by open strings attached to D-branes. After reviewing statistical properties of open strings in D-brane backgrounds, we use dilaton-gravity equations to determine the string frame fields. Although, there are distinctions in the Hagedorn regime thermodynamics and dilaton coupling as compared to closed strings, it seems difficult to avoid Jeans instability and assume thermal equilibrium simultaneously, which is already a known problem for closed strings. We also examine characteristics of a possible subsequent large radius regime in this setup.