Effective Actions for Heterotic M-Theory

TL;DR

This paper derives effective actions for heterotic M-theory with boundary and bulk branes, analyzing the moduli space structure and its implications for cosmological dynamics and perturbations.

Contribution

It extends the moduli space approximation to include bulk branes and reveals a boundary in moduli space causing a hard wall reflection, impacting cosmological models.

Findings

Identification of a boundary in moduli space causing reflection of trajectories.

Analysis of cosmological dynamics with moving branes.

Implications for perturbation behavior in heterotic M-theory.

Abstract

We discuss the moduli space approximation for heterotic M-theory, both for the minimal case of two boundary branes only, and when a bulk brane is included. The resulting effective actions may be used to describe the cosmological dynamics in the regime where the branes are moving slowly, away from singularities. We make use of the recently derived colliding branes solution to determine the global structure of moduli space, finding a boundary at which the trajectories undergo a hard wall reflection. This has important consequences for the allowed moduli space trajectories, and for the behaviour of cosmological perturbations in the model.