Implications of mirror neutrinos for early universe cosmology

The Exact Parity Model (EPM) is, in part, a theory of neutrino mass and mixing that can solve the atmospheric, solar and LSND anomalies. The central feature of the neutrino sector is three pairs of maximally mixed ordinary and mirror neutrinos. It has been shown that ordinary-mirror neutrino oscillations can generate large neutrino asymmetries in the epoch of the early universe immediately prior to Big Bang Nucleosynthesis (BBN). The large neutrino asymmetries generically suppress the production of mirror neutrinos, and a sufficiently large $\nu_e$ asymmetry can directly affect light element synthesis through nuclear reaction rates. In this paper we present a detailed calculation of neutrino asymmetry evolution driven by the six-flavour EPM neutrino sector, focusing on implications for BBN