An improved cosmological bound on the tau-neutrino mass

Abstract

We consider the influence of non-equilibrium electronic neutrinos (and anti-neutrinos) on the neutron-to-proton ratio. These neutrinos would come from massive $\hat{I}{½}_{\ddot{I}}„$ annihilations $\bar{\hat{I}}{½}_{\ddot{I}}„\hat{I}{½}_{\ddot{I}}„\to \bar{\hat{I}}{½}_e\hat{I}{½}_e$. For sufficiently large $\hat{I}{½}_{\ddot{I}}„$ masses this new effect would strongly enhance the (n/p)-ratio, leading to a very stringent bound on the $\hat{I}{½}_{\ddot{I}}„$ mass, even adopting a rather weak upper bound on the effective number on neutrino species during nucleosynthesis.

10 pages, LaTex file + 1 figure compressed using uufiles