Precise Nucleosynthesis Limits on Neutrino Masses

Abstract

A computation of nucleosynthesis bounds on the masses of long-lived Dirac and Majorana neutrinos is reviewed. In particular an explicit treatment of the ``differential heating'' of the $\text{nue}$ and $\text{bnue}$ ensembles due to the residual out-of-equilibrium annihilations of decoupled heavy neutrinos is included. The effect is found to be considerably weaker than recently reported by Dolgov et al. For example, the bounds for a Dirac tau neutrino are $\text{mnt}<0.37$ MeV or $\text{mnt}>25$ MeV (for $\text{dNu}>1$), whereas the present laboratory bound is $\text{mnt}<23.1$ MeV.

Comments: 6 pages, 2 eps-figures. Talk at Neutrino 96