Non-equilibrium corrections to the spectra of massless neutrinos in the early universe Original Research Article

Distortion of the equilibrium spectra of cosmic neutrinos due to interaction with hotter electrons and positrons in the primeval cosmic plasma is considered. The set of integro-differential kinetic equations for neutrinos is accurately numerically solved. The relative corrections to neutrino energy densities are approximately 0.9% for νe and 0.4% for νμ and νπ. This effect results in 1.4 × 10−4 increase in the primordial 4He abundance.