Carnegie Mellon University
Department of Physics
McWilliams Center for Cosmology
Colloquium
Chris Hirata
California Institute of Technology
Wednesday, February 29, 2012
4:30 pm
Doherty Hall A301D
“Understanding the Cosmic Recombination Epoch”
Abstract:
The primary cosmic microwave background anisotropies have proven to be
among the most useful cosmological probes, due to a combination of
impressive observational advances and the simplicity of the underlying
theory -- the CMB is a linear perturbation on a homogeneous and
isotropic background. The most difficult part of the theoretical prediction
for the primary CMB anisotropies has turned out to be the modeling of the
cosmic recombination epoch: the transition from an ionized to neutral
Universe, roughly 400,000 years after the Big Bang, which is the "surface"
that we actually see when we look at the CMB. Even though the early
Universe contained just three elements, computing its recombination
history at the sub-percent level needed for Planck involves a maze of
forbidden transitions, line escape processes, and radiative transfer in the far