NEUTRINO OSCILLATIONS AND THE LEPTONIC CHARGE OF THE UNIVERSE

The most stringent bounds on the individual lepton numbers of the universe arise from considerations of primordial nucleosynthesis. We consider the effect of resonant neutrino flavor oscillations on these limits. In particular, we include the contributions from neutrino-neutrino forward scattering to the effective mass of each neutrino flavor. We find that there can be significant modifications to the neutrino number densities and energy distributions for each flavor over a large range of neutrino vacuum masses and mixing angles. Modifications to the neutrino distributions occurring prior to the nucleosynthesis epoch can substantially alter the previously derived limits on the lepton number for each flavor and its associated degeneracy parameter.