Towards a complete treatment of the cosmological recombination problem
  A new approach to the cosmological recombination problem is presented, which
completes our previous analysis on the effects of two-photon processes during
the epoch of cosmological hydrogen recombination, accounting for ns-1s and
nd-1s Raman events and two-photon transitions from levels with n>=2. The
recombination problem for hydrogen is described using an effective 400-shell
multi-level approach, to which we subsequently add all important recombination
corrections discussed in the literature thus far. We explicitly solve the
radiative transfer equation of the Lyman-series photon field to obtain the
required modifications to the rate equations of the resolved levels. In
agreement with earlier computations we find that 2s-1s Raman scattering leads
to a delay in recombination by DN_e/N_e~0.9% at z~920. Two-photon decay and
Raman scattering from higher levels (n>3) result in a small additional
modifications, and precise results can be obtained when including their effect
for the first 3-5 shells. This work is a major step towards a new cosmological
recombination code (CosmoRec) that supersedes the physical model included in
Recfast, and which, owing to its short runtime, can be used in the analysis of
future CMB data from the Planck Surveyor.
