Unstable massive tau-neutrinos and primordial nucleosynthesis
Abstract
The impact of unstable Majorana tau neutrinos on primordial nucleosynthesis is considered. The mass and lifetime of nutau are taken in the intervals 0.1-20 MeV and 0.001-400 sec respectively. The studied decay modes are nutau -> numu + phi and nutau -> nue + phi, where phi 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 nutau, the number of effective neutrino species (found from He4), in addition to the 3 standard ones, varies from -2 to +2.5. The abundances of H2 and Li7 are also calculated.
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