Cosmological hydrogen recombination: the effect of very high-n states and quadrupole transitions.

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Thanks to the ongoing Planck mission, a new window will be opened on the
properties of the primordial density field, the cosmological parameters,
and the physics of reionization. Much of Planck's new leverage on these
quantities will come from temperature measurements at small angular
scales and from polarization measurements. These both depend on the
details of cosmological hydrogen recombination; use of the CMB as a
probe of energies greater than 10^16 GeV compels us to get the ~eV scale
atomic physics right.

One question that remains is how high in hydrogen principle quantum
number we have to go to make sufficiently accurate predictions for
Planck. Using sparse matrix methods to beat computational difficulties,
I have modeled the influence of very high (up to and including n=200)
excitation states of atomic hydrogen on the recombination history of the
primordial plasma, resolving all angular momentum sub-states separately
and including, for the first time, the effect of hydrogen quadrupole
transitions. I will review the basic physics, explain the resulting
plasma properties, discuss recombination histories, and close by
discussing the effects on CMB observables.