Cosmological Perturbations in the 5D Holographic Big Bang Model
  The 5D Holographic Big Bang is a novel model for the emergence of the early
universe out of a 5D collapsing star (an apparent white hole), in the context
of Dvali-Gabadadze-Porrati (DGP) cosmology. The model does not have a big bang
singularity, and yet can address cosmological puzzles that are traditionally
solved within inflationary cosmology. In this paper, we compute the exact power
spectrum of cosmological curvature perturbations due to the effect of a thin
atmosphere accreting into our 3-brane. The spectrum is scale-invariant on small
scales and red on intermediate scales, but becomes blue on scales larger than
the height of the atmosphere. While this behaviour is broadly consistent with
the non-parametric measurements of the primordial scalar power spectrum, it is
marginally disfavoured relative to a simple power law (at 2.7$\sigma$ level).
Furthermore, we find that the best fit nucleation temperature of our 3-brane is
at least 3 orders of magnitude larger than the 5D Planck mass, suggesting an
origin in a 5D quantum gravity phase.
