Interaction Rates in String Gas Cosmology

TL;DR

This paper investigates string interaction rates in early universe string gas cosmology, demonstrating their negligibility and challenging the assumption of thermal equilibrium, with numerical and analytical analyses of string dynamics.

Contribution

It provides a new analysis of string interaction rates and cosmological evolution in the Brandenberger-Vafa scenario, highlighting the importance of quantum effects and large-radius modifications.

Findings

String interaction rates are negligible in the early universe.

Thermal equilibrium assumptions are invalid for string gases.

Quantum mechanics significantly affects string annihilation rates.

Abstract

We study string interaction rates in the Brandenberger-Vafa scenario, the very early universe cosmology of a gas of strings. This cosmology starts with the assumption that all spatial dimensions are compact and initially have string scale radii; some dimensions grow due to some thermal or quantum fluctuation which acts as an initial expansion velocity. Based on simple arguments from the low energy equations of motion and string thermodynamics, we demonstrate that the interaction rates of strings are negligible, so the common assumption of thermal equilibrium cannot apply. We also present a new analysis of the cosmological evolution of strings on compact manifolds of large radius. Then we discuss modifications that should be considered to the usual Brandenberger-Vafa scenario. To confirm our simple arguments, we give a numerical calculation of the annihilation rate of winding strings. In calculating the rate, we also show that the quantum mechanics of strings in small spaces is important.