Behavior of tachyon in string cosmology based on gauged WZW model

TL;DR

This paper explores the dynamics of tachyon fields in a string cosmology model based on gauged WZW theory, revealing their dominance in early universe and violations of classical energy conditions.

Contribution

It extends previous semiclassical models by analyzing finite Kac-Moody levels, incorporating tachyon fields into the effective action, and examining their impact on early universe conditions.

Findings

Tachyon dominates over dilaton in early times.

Energy conditions are violated, including strong and null energy conditions.

Tachyon behavior is characterized as a function of time in the model.

Abstract

We investigate a string theoretic cosmological model in the context of the gauged Wess-Zumino-Witten model. Our model is based on a product of non-compact coset space and a spectator flat space; $[SL(2,R)/U(1)]_k \times {\bf R}^2$. We extend the formerly studied semiclassical consideration with infinite Kac-Moody level $k$ to a finite one. In this case, the tachyon field appears in the effective action, and we solve the Einstein equation to determine the behavior of tachyon as a function of time. We find that tachyon field dominates over dilaton field in early times. In particular, we consider the energy conditions of the matter fields consisting of the dilaton and the tachyon which affect the initial singularity. We find that not only the strong energy but also the null energy condition is violated.