We analyze the effects of lepton asymmetry on neutrino oscillations and on cosmological nucleosynthesis with active-sterile oscillating neutrinos .
It is shown that small lepton asymmetries , L < 0.01 , whose direct kinetic effect on nucleosynthesis is negligible , still effect nucleosynthesis considerably through their influence on oscillating neutrinos .
Two different cases of lepton asymmetry are discussed : an initially present and a dynamically generated in oscillations . Dynamically generated in resonant oscillations asymmetry at small mixing angles suppresses oscillations , hence , the nucleosynthesis bounds on neutrino mass differences at small mixings are relaxed . Initially present asymmetry may suppress or enhance oscillations .
The enhancement is a result of interchanging resonances between neutrino and antineutrino ensembles due to resonance waves passing through the neutrino and antineutrino spectrum .
Updated nucleosynthesis bounds on neutrino oscillation parameters accounting for lepton asymmetry are presented .