Detailed study of BBN implications of neutrino oscillation generated neutrino asymmetries in some four neutrino models

We re-examine the evolution of neutrino asymmetries in several four neutrino models. The first case involves the direct creation of Lνe by νe ↔ νs oscillations. In the second case, we consider the mass hierarchy mντ >> mνμ, mνe, mνs where ντ ↔ νs oscillations generate a large Lντ and some of this asymmetry is converted into Lνe by ντ ↔ νe oscillations. We estimate the implications for Big Bang Nucleosynthesis (BBN) for a range of cosmologically interesting δm2 values. The present paper improves on a previous study by taking into account the finite repopulation rate and the time dependence of the distortions to the neutrino momentum distributions. The treatment of chemical decoupling is also improved. It is expected that accurate determinations of the primordial element abundances, as well as forthcoming precision measurements of the anisotropy of the cosmic microwave background may one day help to distinguish between competing models of particle physics