Investigation of the electromagnetically induced transparency in the era of cosmological hydrogen recombination

Investigation of cosmic microwave background formation processes is one of the most compelling problems at the present time. In this paper we analyse the response of the hydrogen atom to external photon fields. Field characteristics are defined via conditions corresponding to the recombination era of the universe. Approximation of the three-level atom is used to describe the 'atom-field' interaction. It is found that the phenomena of the electromagnetically induced transparency (EIT) take place in this case. Consideration of EIT phenomena makes it necessary to update the astrophysical description of the processes of cosmic microwave background formation and, in particular, the Sobolev escape probability. Additional terms to the optical depth entering in the Sobolev escape probability are found to contribute on the level about 1%.