Gauges in the Bulk II: Models with Bulk Scalars

TL;DR

This paper develops effective low-energy theories for braneworld models with bulk scalar fields, including BPS and non-BPS configurations, and clarifies the role of moduli space approximation in these models.

Contribution

It constructs scalar-tensor effective actions for Randall-Sundrum type models with bulk scalars, applicable even with brane-matter coupling, and clarifies the nature of the moduli space approximation.

Findings

Derived scalar-tensor theories with one scalar degree of freedom.

Applicable to models with direct bulk-brane matter coupling.

Revealed that the moduli space approximation describes non-BPS three-brane systems.

Abstract

Extending previous work in Randall-Sundrum type models, we construct low-energy effective actions for braneworlds with a bulk scalar field, with special attention to the case of BPS branes. Holding the branes at fixed coordinate position with a general ansatz for the bulk metric, and imposing the Einstein frame as a gauge condition, we obtain a scalar-tensor theory with only one scalar degree of freedom related to the proper brane separation. The formalism is applicable even when there is direct coupling of the bulk scalar and brane matter, as in the Horava-Witten model. We further show that the usual moduli space approximation actually describes a non-BPS three-brane system.