"Just so" neutrino oscillations are back

Recent evidence for oscillations of atmospheric neutrinos at Super-Kamiokan de suggest, in the simplest see-saw interpretation, neutrino masses such th at "just so" vacuum oscillations can explain the solar neutrino deficit. Su per-K solar neutrino data provide preliminary support for this interpretati on. We describe how the just-so signal - an energy dependent seasonal varia tion of the event rate, might be detected within the coming years and provi de general arguments constraining the sign of the variation. The expected v ariation at radiochemical detectors may be below present sensitivity, but a significant modulation in the Be-7 signal could shed light on the physics of the solar core - including a direct measure of the solar core temperatur e. (C) 1999 Elsevier Science B.V. All rights reserved.