neutrino oscillations

The original B. Pontecorvo idea of neutrino oscillations is discussed. Neutrino mixing and basics of neutrino oscillations in vacuum and in matter are considered. Recent evidences in favour of neutrino oscillations, obtained in the Super-Kamiokande, SNO, KamLAND and other neutrino experiments are discussed. Neutrino oscillations in the solar and atmospheric ranges of the neutrino mass-squared differences are considered in the framework of the minimal scheme with the mixing of three massive neutrinos. Results of the tritium β-decay experiments and experiments on the search for neutrinoless double β-decay are briefly discussed. 1 Pontecorvo idea of neutrino oscillations B. Pontecorvo came to the idea of neutrino oscillations in 1957, soon after parity violation in β-decay was discovered by Wu et. al. [1] and the two-component theory of massless neutrino was proposed by Landau [2], Lee and Yang [3] and Salam [4]. For the first time B.Pontecorvo mentioned the possibility of neutrino ⇄ antineutrino transitions in vacuum in his paper [5] on muonium ⇄ antimuo-nium transition (µ − e + ⇄ µ + e −). He believed in the analogy between the weak interaction of leptons and hadrons and looked in the lepton world for a phenomenon that would be analogous to K 0 ⇄ K 0 oscillations. In his work of 1957 [5] B. Pontecorvo wrote: 1 Dedicated to B. Pontecorvo in 90th anniversary of his birth.