Low Energy Effective Action for Horava-Witten Cosmology

TL;DR

This paper derives a 4D effective action from a 5D supersymmetric brane-world model with a bulk scalar, revealing Einstein gravity coupled with two scalar fields related to brane separation and bulk scalar dynamics.

Contribution

It provides a detailed derivation of the low energy effective action for a Horava-Witten type model, connecting bulk dynamics to 4D gravity with scalar fields.

Findings

Effective 4D action expressed as Einstein gravity with two scalars

Identification of radion and bulk scalar as key degrees of freedom

Clarification of relation to moduli approximation

Abstract

As a supersymmetric extension of the Randall-Sundrum model, we consider a 5-dimensional Horava-Witten type theory, and derive its low energy effective action. The model we consider is a two-brane system with a bulk scalar field satisfying the BPS condition. We solve the bulk equations of motion using a gradient expansion method, and substitute the solution into the original action to get the 4-dimensional effective action. The resultant effective theory can be casted into the form of Einstein gravity coupled with two scalar fields, one arising from the radion, the degree of freedom of the inter-brane distance, and the other from the bulk scalar field. We also clarify the relation between our analysis and the moduli approximation.