The Status of Neutrino Mass

Abstract

New experimental results, if correct, require at least one light sterile neutrino, in addition to the three active ones, to accommodate the mass differences required to explain the solar $\nu_e$ deficit, the anomalous $\nu/e$ ratio produced by atmospheric neutrinos, and either the candidate events for $\nu_\mu\to\nu_e$ (or $\bar\nu_\mu\to\bar\nu_e$) from the LSND experiment, or the possible need for a hot component of dark matter. This neutrino mass pattern can not only accommodate all these four requirements, but also provide a robust solution to a problem presently making heavy-element synthesis by supernovae impossible and resolve a possible discrepancy between big bang nucleosynthesis theory and observations.