Renormalisation Effects of Neutrino Masses and Interactions

The Super-Kamiokande data [1] clearly indicate a νμ/νe ratio in the atmosphere that is significantly smaller than the theoretical expectations. The most natural way to explain this deviation is by introducing νμ–ντ oscillations, with δmνμντ ≈ (10−2 to 10−3) eV2 and sin 2θμτ ≥ 0.85. Alternative schemes with dominant νμ → νe oscillations are excluded by both the Super-Kamiokande data on electron-like events [1], and the Chooz reactor experiment [2]. Finally, oscillations involving a sterile neutrino are disfavoured (but not yet excluded) by the azimuthal-angle dependence of muon-like events [1] and by measurements of π0 production. Once neutrino oscillations are introduced in order to explain the atmospheric neutrino deficit, it is natural to address similarly the solar neutrino puzzle. The latter can be resolved through either vacuum or matterenhanced (MSW) oscillations. The first require a mass splitting of the ∗ Invited talk at the Cracow Epiphany Conference on Neutrinos in Physics and Astrophysics, January 2000