Nonresonant effects and hydrogen transition line shape in cosmological recombination problems

Data on the fluctuations in cosmic microwave background (CMB) radiation, whose accuracy is expected to increase in the immediate future, allow the cosmological recombination of atomic hydrogen and its interaction with the CMB radiation to be studied. Nonresonant effects play an important role in these recombination processes. We consider the quantum-mechanical foundations of the nonresonant processes and present our calculations for the differential two-photon decay rates of the 3s and 3d levels in the hydrogen atom.