Neutrino spectrum distortion due to oscillations and its BBN effect

摘要

We study the distortion of electron neutrino energy spectrum due to oscillations with the sterile neutrino v(e)<---->v(s), for different initial populations of the sterile state deltaN(s) at the onset of oscillations. The influence of this spectrum distortion on Big Bang Nucleosynthesis is analyzed. Only the case of an initially empty sterile state was studied in previous publications.The primordial abundance of He-4 is calculated for all possible deltaN(s): 0 less than or equal to deltaN(s) less than or equal to 1 in the model of oscillations, effective after electron neutrino decoupling, for which the spectrum distortion effects on the neutron-proton transitions are the strongest.It is found that the spectrum distortion effect may be dominant, not only in the case of small deltaN(s), but also in the case of large initial population of v(s). For example, in the resonant case it may play a considerable role even for very large deltaN(s) similar to 0.8. Cosmological constraints on neutrino mixing for small deltaN(s) are discussed.