Thermal history of the string universe

TL;DR

This paper investigates the thermal evolution of the string universe within the Brandenberger-Vafa framework, establishing a thermodynamically consistent initial oscillating phase and refining the multi state density model near the Hagedorn temperature.

Contribution

It introduces a new method to accurately evaluate the multi state density of string gas, correcting the traditional functional form near the Hagedorn temperature.

Findings

The initial oscillating phase is thermodynamically natural.

A revised multi state density form is derived for $T \,\leq\, T_H$.

The analysis supports the string universe scenario with a solid theoretical basis.

Abstract

Thermal history of the string universe based on the Brandenberger and Vafa's scenario is examined. The analysis thereby provides a theoretical foundation of the string universe scenario. Especially the picture of the initial oscillating phase is shown to be natural from the thermodynamical point of view. A new tool is employed to evaluate the multi state density of the string gas. This analysis points out that the well-known functional form of the multi state density is not applicable for the important region $T \leq T_H$, and derives a correct form of it.