Precise Nucleosynthesis Limits on Neutrino Masses

Original · EN

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 and 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 < 0.37 MeV or > 25 MeV (for > 1), whereas the present laboratory bound is < 23.1 MeV.