On Lepton asymmetry and BBN

The strongest available cosmological constraint on lepton asymmetry is L < 0.01 . We discuss in more detail a BBN model with late ν e ↔ ν s oscillations which is capable of measuring extremely small lepton asymmetry, L > 1 0 − 8 . This sensitivity is achieved through the influence of small L 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 L on nucleons freezing in pre-BBN epoch is numerically analyzed in the full range of the oscillation parameters for the model and L ≥ 1 0 − 10 .