The annihilation process νanti ν → γγ with massive neutrinos in cosmology

The amplitude for νanti ν → γγ is shown to be dominated by the term linear in the neutrino mass msub(ν) for msub(ν) approx. >= 1 eV and energies approx. <= 1 MeV. This term involves the AVV triangle function, for which a representation in terms of elementary functions is found. We give an improved estimate of energy loss from stars via γγ → νanti ν. Structures of gravitationally bound neutrinos on a cosmological scale, 'neutrino stars', are studied. On that basis it is shown that νanti ν → γγ must be unimportant in cosmological particle equilibria unless msub(ν) >> 30 eV. (orig.)