The exact parity symmetric model and big bang nucleosynthesis

The assumption of exact, unbroken parity symmetry leads directly to a simple pre-dictive resolution of the atmospheric and solar neutrino puzzles. This is because the existence of this symmetry implies the existence of a set of mirror neutrinos which must mix maximally with the known neutrinos if neutrinos have mass. The maximal mixing of the electron neutrino with the mirror electron neutrino with 3 × 10 −10 eV 2 < ∼ |δm 2 | < ∼ 10 −3 eV 2 leads to a predicted reduction of the solar neutrino flux by a factor of 2, which is in quite good agreement with the experiments. The maximal mixing of the muon neutrino with the mirror muon neutrino with |δm 2 | ≃ 10 −2 eV 2 also solves the atmospheric neutrino puzzle. We show that there is a significant range of parameters where these solutions are not in conflict with standard Big Bang Nucleosynthesis when the creation of lepton asymmetry due to neutrino oscillations is taken into account.