Cosmological perturbations in brane-world theories: Formalism - art. no. 123515

We develop a gauge-invariant formalism to describe metric perturbations in five-dimensional brane-world theories. In particular, this formalism applie s to models originating from heterotic hi theory. We introduce a generalize d longitudinal gauge for scalar perturbations. In this gauge, we derive the five-dimensional evolution equations for scalar perturbations as well as t he most general structure of the scalar brane stress-energy tensor. As an a pplication, 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-dim ensional description is appropriate.