Abstract
The familiar nucleosynthesis constraint on the number of neutrino species, ≤3.4, applies to massless neutrino species. An MeV-mass neutrino can have even greater impact, and we show that primordial nucleosynthesis excludes a τ-neutrino mass from 0.3 to 25 MeV (Dirac) and 0.5 to 25 MeV (Majorana) provided that its lifetime ≳1 sec, and from 0.3 to 30 MeV (Dirac) and 0.5 to 32 MeV (Majorana) for ≳ sec. A modest improvement in the laboratory mass limit—from 35 to 25 MeV—would imply that the τ-neutrino mass must be less than 0.5 MeV (provided ≳1 sec).
- Received 4 February 1991
DOI:https://doi.org/10.1103/PhysRevLett.67.533
©1991 American Physical Society