paper

Primordial Nucleosynthesis, Majorons and Heavy Tau Neutrinos

arXiv:hep-ph/9610507 · doi:10.1016/S0550-3213(97)00213-7

Abstract

We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of nu-tau annihilations into Majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species as a function of nu-tau mass and the nu-tau-Majoron coupling . We show that for theoretically plausible values $\gsim 10^{-4}$ present nucleosynthesis observations can not rule out nu-tau masses in the MeV range. Moreover, these models give in the nu-tau mass region 1-10 MeV, for very reasonable values of . The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the nu-tau mass which can be achieved at a tau-charm factory.

20 pages, LaTex + 6 ps figures. Discussion of the majoron couplings is clarified in new appendix. To be published in NPB

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