Weak-interaction-induced neutrino oscillations

Neutrino oscillation is a natural theoretical possibility in gauge theories if we do not a priori exclude the right-hand components of neutrino fields. The quantitative aspects of the oscillation phenomenon (oscillation length, etc. ) are controlled by the neutrino mass matrix. We explore the possibility that neutrinos are massless in the lowest order of weak interactions and higher-order radiative corrections bring about small, but calculable, masses. We have made a systematic search of models which would have such a feature. We find that in one class of models, the neutrino-mass matrix elements would generally be less than 10^-2 eV. But such theories would contain flavor-changing neutral currents involving charged lepton fields. Another class of models, which can easily be compatible with all known weak-interaction phenomenology, would necessarily involve large gauge groups (e. g. , direct products of at least three non-Abelian factors) and a large number of unknown parameters (making it impossible to meaningfully estimate the neutrino masses).