Radion and Large Scale Anisotropy on the Brane

Abstract

We investigate the effect of displacements of the brane in the extra dimension. The S 1 /Z 2 compactified 5D anti-de Sitter spacetime bounded by positive and negative tension branes is considered. The relative displacementof a brane is called a radion''. We study displacements caused by the of a brane without the matter energy-momentum tensor on the brane. We derive the solution for a homogeneous fluctuation of an expanding brane. It is found that the homogeneous brane fluctuation interacts with an anisotropic bulk perturbation and thereby affects the anisotropy of the brane. By determining the bulk anisotropic perturbation, we calculate the homogeneous metric perturbations on the positive tension brane and find a large-scale CMB anisotropy. An interesting finding is that the radion contributes to the CMB anisotropy if the distance between the two branes is time dependent. The observational consequences of these effects are discussed.