Perturbations on and off de Sitter brane in anti-de Sitter bulk
  Motivated by holographic models of (pseudo)conformal Universe, we carry out
complete analysis of linearized metric perturbations in the time-dependent
two-brane setup of the Lykken-Randall type. We present the equations of motion
for the scalar, vector and tensor perturbations and identify light modes in the
spectrum, which are scalar radion and transverse-traceless graviton. We show
that there are no other modes in the discrete part of the spectrum. We pay
special attention to properties of light modes and show, in particular, that
the radion has red power spectrum at late times, as anticipated on holographic
grounds. Unlike the graviton, the radion survives in the single-brane limit,
when one of the branes is sent to the adS boundary. These properties imply that
potentially observable features characteristic of the 4d (pseudo)conformal
cosmology, such as statistical anisotropy and specific shapes of
non-Gaussianity, are inherent also in holographic conformal models as well as
in brane world inflation.
