Cosmological implications of massive, unstable neutrinos

Abstract

The cosmological consequences of the existence of massive, neutral, weakly interacting leptons are considered. Bounds are calculated on the lepton mass, lifetime, and allowed interaction strength by assuming minimal modification of the standard big-bang model. The chief conclusions are: the lepton may be stable if its mass is greater than a few GeV; for intermediate masses, for which the lepton must be unstable, if its principal decay mode creates photons, masses less than 0.01 MeV are ruled out and its lifetime must be less than 1 year; if the lepton decays exclusively into neutrinos, it may have a considerably longer lifetime and give rise to a present-day energy density sufficiently high to make the universe radiation-dominated and closed.