Effective action for the homogeneous radion in brane cosmology

TL;DR

This paper derives an exact four-dimensional effective action for the radion field in two-brane cosmological models with AdS bulk, capturing its non-perturbative dynamics and comparing it with full five-dimensional behavior.

Contribution

It provides the first explicit, non-perturbative derivation of the radion's effective action in de Sitter brane models, including Minkowski as a special case.

Findings

Explicit effective action for the radion in de Sitter branes

Comparison between 4D effective dynamics and 5D true dynamics

Insights into radion behavior in brane cosmology

Abstract

We consider cosmological two-brane models with AdS bulk, for which the radion, i.e. the separation between the two branes, is time dependent. In the case of two de Sitter branes (including Minkowski branes as a limiting case), we compute explicitly, without any approximation, the effective four-dimensional action for the radion. With the scale factor on-shell, this provides the non-perturbative dynamics for the radion. We discuss the differences between the dynamics derived from the four-dimensional action with the scale factor off-shell and the true five-dimensional dynamics.