Tensor perturbations

6.6 Tensor perturbations

The covariant description of tensor modes on the brane is via the shear, which satisfies the wave equation [219 ]

Unlike the density and vector perturbations, there is no closed system on the brane for large scales. The KK anisotropic stress $¯πℰμν$ is an unavoidable source for tensor modes on the brane. Thus it is necessary to use the 5D metric-based formalism. This is the subject of the next Section 7.