Unstable massive tau-neutrinos and primordial nucleosynthesis Original Research Article

The impact of unstable Majorana ντ on primordial nucleosynthesis is considered. The mass and lifetime of ντ are taken in the intervals 0.1–20 MeV and 0.001–400 s respectively. The studied decay modes are ντ → νμ + φ and ντ → νe + φ, where φ is a massless (or light) scalar. Integro-differential kinetic equations are solved numerically without any simplifying assumptions. Our results deviate rather strongly from earlier calculations. Depending on mass, lifetime, and decay channels of the ντ, the number of effective neutrino species (found from 4He), in addition to the 3 standard ones, varies from −2 to +2.5. The abundances of 2H and 7Li are also calculated.