On Neutrino-Mixing-Generated Lepton Asymmetry and the Primordial Helium-4 Abundance

Abstract

In this article we discuss lepton asymmetry effect on BBN with neutrino oscillations. We argue that asymmetry much smaller than 0.01, although not big enough to influence directly the nucleosynthesis kinetics, can effect considerably BBN indirectly via neutrino oscillations. Namely, it distorts neutrino spectrum and changes neutrino density evolution and the pattern of oscillations (either suppressing or enhancing them), which in turn effect the primordial synthesis of elements. We show that the results of the paper X. Shi et al., Phys. Rev. D 60, 063002 (1999), based on the assumption that only L > 0.01 will influence helium-4 production, are not valid. Instead, the precise constraints on neutrino mixing parameters from BBN are presented.