Aspects of the theory of neutrino mass

Abstract

The models of neutrino mass are briefly reviewed. Since they give at best only qualitative features of the neutrino mass, additional constraints are considered. Cosmology restricts the masses of stable neutrinos and lifetimes of the unstable ones. Neutrino counting (Z‐width and primordial nucleosynthesis) restrict the number of neutrino flavors. Neutrino double beta decay constrains the mass eigenvalues. All these features have to be considered when new evidence (e.g., the recent suggestion of 17 keV neutrino) are placed in the broader context.