On Lepton asymmetry and BBN

The strongest available cosmological constraint on lepton asymmetry is L<0.01L<0.01. We discuss in more detail a BBN model with late νe↔νsνe↔νs oscillations which is capable of measuring extremely small lepton asymmetry, L>10−8L>10−8. This sensitivity is achieved through the influence of small LL on the neutrino oscillations, suppressing or enhancing them, and thus decreasing or increasing the primordially produced 4He. The cases of asymmetry generated by late resonant electron-sterile oscillations and relic lepton asymmetry are considered. The influence of LL on nucleons freezing in pre-BBN epoch is numerically analyzed in the full range of the oscillation parameters for the model and L≥10−10L≥10−10.