Impact of massive tau-neutrinos on primordial nucleosynthesis. Exact calculations
arXiv:hep-ph/9712284 · doi:10.1016/S0550-3213(98)00307-1
Abstract
The influence of a massive Majorana tau-neutrino on primordial nucleosynthesis is rigorously calculated. The system of three integro-differential kinetic equations is solved numerically for the tau-neutrino mass in the interval from 0 to 20 MeV. It is found that the usual assumption of kinetic equilibrium is strongly violated and non-equilibrium corrections considerably amplify the effect. Even a very weak restriction from nucleosynthesis, allowing for one extra massless neutrino species, permits to conclude that m_ν_τ< 1 MeV. For a stricter bound, e.g. for dN < 0.3, the limit is m_ν_τ< 0.35 MeV.
30 pages, 9 figures, 2 tables, revised figures, minor changes