Neutrino physics and astrophysics

The implications of primordial nucleosynthesis on neutrino masses, magnetic moments, and mixing angles are discussed. Right‐handed helicity states of a Dirac neutrino may be excited by collisions unless the mass and the magnetic moment are small enough. The observed galactic magnetic fields may also set limits on the Dirac neutrino masses and magnetic moments. Oscillations between inert and flavor state neutrinos are severely constrained by primordial nucleosynthesis, and useful bounds can be obtained for the oscillation explanations of the solar and atmospheric neutrino fluxes, as well as the Majoron models with pseudo–Dirac neutrinos.