Generality of Singularity Avoidance in Superstring Theory: Anisotropic Case

TL;DR

This paper investigates the stability of nonsingular cosmological solutions in superstring theory, finding that such solutions exist in anisotropic Bianchi I models but not in Bianchi IX models, suggesting instability of nonsingular universes.

Contribution

It extends the analysis of singularity avoidance in superstring cosmology to anisotropic cases, showing the instability of nonsingular solutions in Bianchi IX models.

Findings

Nonsingular solutions exist in Bianchi I models.

No nonsingular solutions found in Bianchi IX models.

Instability of nonsingular universes in anisotropic models.

Abstract

In one-loop string effective action, we study a generality of non-singular cosmological solutions found in the isotropic and homogeneous case. We discuss Bianchi I and IX type spacetimes. We find that nonsingular solutions still exist in Bianchi I model around nonsingular flat Friedmann solutions. On the other hand, we cannot find any nonsingular solutions in Bianchi IX model. Non-existence of nonsingular Bianchi IX universe may be consistent with the analysis by Kawai, Sakagami and Soda, i.e. the tensor mode perturbations against nonsingular flat Friedmann universe are unstable, because Bianchi IX model can be regarded as a closed Friedmann universe with a single gravitational wave. So based on these facts, we may conclude the nonsingular universe is found in isotropic case is generally unstable, a singularity avoidance may not work in the present model.