SSP2012 - 5th International Symposium on Symmetries in Subatomic Physics

We discuss the interplay between lepton asymmetry L and neutrino oscillations in the early Universe. Neutrino oscillations may suppress or enhance previously existing L. On the other hand L is capable to suppress or enhance neutrino oscillations. The mechanism of L enhancement in resonant neutrino oscillations in the early Universe is numerically analyzed. Lepton asymmetry cosmological effects through neutrino oscillations are studied. It is shown how L changes the BBN constraints on neutrino and how the BBN model with electron-sterile neutrino oscillations constrains lepton asymmetry. This model allows to obtain the most stringent constraints on L value. We discuss also the cosmological role of active-inert neutrino mixing and L in connection with the indications about additional relativistic density in the early Universe, pointed out by BBN, CMB and LSS data and the analysis of global neutrino data.