On the Classical Stability of Orientifold Cosmologies

TL;DR

This paper investigates the classical stability of string cosmologies involving orientifold planes, demonstrating that orientifolds resolve instabilities present in pure orbifold models and ensuring the stability of the cosmological Cauchy horizon.

Contribution

It shows that orientifold planes stabilize string cosmologies by resolving orbifold singularities and preventing instabilities in the Cauchy horizon.

Findings

Instability in pure orbifold models is resolved by orientifolds.

The cosmological Cauchy horizon remains stable under small perturbations.

Orientifold-driven models are robust against in-falling matter perturbations.

Abstract

We analyze the classical stability of string cosmologies driven by the dynamics of orientifold planes. These models are related to time-dependent orbifolds, and resolve the orbifold singularities which are otherwise problematic by introducing orientifold planes. In particular, we show that the instability discussed by Horowitz and Polchinski for pure orbifold models is resolved by the presence of the orientifolds. Moreover, we discuss the issue of stability of the cosmological Cauchy horizon, and we show that it is stable to small perturbations due to in-falling matter.