Linearized Israel Matching Conditions for Cosmological Perturbations in a Moving Brane Background

TL;DR

This paper derives covariant linearized Israel matching conditions for cosmological perturbations in Randall-Sundrum models with a moving brane, ensuring gauge consistency and characterizing residual gauge freedoms.

Contribution

It introduces a fully covariant, local gauge approach for linearized perturbations in brane cosmology, avoiding nonlocal scalar-vector-tensor decompositions.

Findings

Derived covariant boundary conditions for bulk gravitons.

Ensured gauge consistency during graviton reflection off the brane.

Characterized residual gauge freedoms including brane displacements.

Abstract

With a view toward the problem of computing the linearized cosmological perturbations in Randall-Sundrum cosmological models where a Z2 symmetry has been imposed about a boundary brane, we derive the form of the linearized Israel matching conditions and the auxiliary gauge conditions on the boundary when Lorentz gauge has been imposed in the bulk. This gauge is completely covariant and local, manifestly respecting all the AdS5 symmetries in the bulk and not relying on a decomposition into pure scalar, vector, and tensor sectors, which is necessarily nonlocal. We demonstrate that the auxiliary gauge conditions on the boundary ensure that bulk gravitons upon reflection off the brane do not emit polarizations that violate the bulk Lorentz gauge condition. We also characterize the residual gauge freedom, embodied by five longitudinal (pure gauge) graviton polarizations in the bulk, four of which correspond to reparameterizations of the induced brane metric and one of which corresponds to normal displacements of the brane.