Constraints on String Cosmology

TL;DR

This paper investigates the limitations of string cosmology, showing that while de Sitter solutions remain impossible, anti-de Sitter solutions can occur due to higher derivative interactions in heterotic string compactifications.

Contribution

It demonstrates how higher derivative interactions in heterotic string theory enable anti-de Sitter solutions, challenging previous constraints on string cosmology models.

Findings

De Sitter solutions remain impossible in this context.

Anti-de Sitter solutions are classically allowed.

Higher derivative interactions enable new solutions.

Abstract

String theory contains sources like orientifold planes that support higher derivative interactions. These interactions make possible static flux compactifications which are forbidden in supergravity. They can also lead to violations of the strong energy condition (SEC) which is needed for an accelerating universe. We examine how large a violation is possible in the context of the heterotic string compactified to four dimensions. We find that de Sitter solutions are still not possible but that classically forbidden anti-de Sitter solutions are possible.