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 ${\nu }_{\tau }$ annihilations ${\bar{\nu }}_{\tau }{\nu }_{\tau }\to {\bar{\nu }}_e{\nu }_e$. For sufficiently large ${\nu }_{\tau }$ masses this new effect would strongly enhance the (n/p)-ratio, leading to a very stringent bound on the ${\nu }_{\tau }$ mass, even adopting a rather weak upper bound on the effective number on neutrino species during nucleosynthesis.

Comments: 10 pages, LaTex file + 1 figure compressed using uufiles