“Just so” neutrino oscillations

Abstract

We examine in detail the possibility that the low rates observed in the chlorine solar neutrino experiment are due to vacuum oscillations between just two neutrino species — a possibility which remains viable over a finite mass range. We calculate the expected signals, seasonal variations, and effects of time-averaging for both chlorine and gallium based solar neutrino detectors. These provide unique signals for such oscillations, and thus also allow them to be distinguished from the recently proposed resonant neutrino conversion process, as well as from other possible causes of the observed suppression. Finally we display several striking signatures of oscillations relevant to future experiments which may be sensitive to the incident neutrino energy spectrum.