Nucleosynthesis bounds on small Dirac neutrino masses due to chiral   symmetry breaking
  We consider nucleosynthesis constraints on models which use chiral symmetry breaking as a basis for understanding very small Dirac neutrino masses. We show that present big-bang nucleosynthesis constraints impose a well-defined upper bound of 0.1eV on the neutrino masses. This bound may become several orders of magnitude more stringent in the future as our understanding of the observational constraints on nucleosynthesis improves. We discuss the phenomenological implications for neutrino dark matter, the solar neutrino problem and the atmospheric neutrino deficit. 
John McDonald (Lancaster University, UK)