Cosmological Perturbations in Brane-World Theories: Formalism

TL;DR

This paper develops a gauge-invariant formalism for analyzing metric perturbations in five-dimensional brane-world theories, especially those from heterotic M-theory, and connects it to four-dimensional models.

Contribution

It introduces a generalized longitudinal gauge and a formalism that bridges five-dimensional and four-dimensional descriptions of cosmological perturbations.

Findings

Formalism applies to heterotic M-theory models.

Provides a method to analyze fluctuation evolution on the brane.

Shows how 5D formalism reduces to 4D in certain limits.

Abstract

We develop a gauge-invariant formalism to describe metric perturbations in five-dimensional brane-world theories. In particular, this formalism applies to models originating from heterotic M-theory. We introduce a generalized longitudinal gauge for scalar perturbations. As an application, we discuss some aspects of the evolution of fluctuations on the brane. Moreover, we show how the five-dimensional formalism can be matched to the known four-dimensional one in the limit where an effective four-dimensional description is appropriate.