Neutrino Masses and Oscillations

Abstract

The year 2013 marks the 100th anniversary of the birth of Bruno Pontecorvo, who first suggested the possibility that neutrinos might have a nonzero mass such that oscillations among different neutrino states might occur. Pontecorvo constantly pursued this idea, after the discovery of other neutrino flavours, until his death. This issue is intended as a contribution to the celebration of this anniversary, by collecting a number of articles on neutrino masses and neutrino oscillations, both of which have been the subject of extensive studies and have seen a tremendous progress over the last decades. The subject of neutrino mass acquires an even bigger interest after the recent announcement of the existence of a new boson which is likely to be the elusive Higgs boson. This represents a beautiful confirmation of several aspects of the standardmodel.However, in the present formulation of the standard model neutrinos are massless, in contradiction with their tiny masses as inferred by oscillation experiments. Some models link this smallness to the existence of very heavy mass states, thus opening a window on a much higher mass scale. Therefore, the issues of neutrino mass and of lepton number violation add an unprecedented momentum in the quest for new physics beyond the standard model. This issue includes the article “Bruno pontecorvo and neutrino oscillations” by S. M. Bilenky, a longtime close collaborator of Bruno Pontecorvo, who gives an overview of the large number of ideas proposed by Pontecorvo, which originated a vast number of both experimental and theoretical developments. The original ideas (1957-58) are first considered in this paper. This is followed by the consideration of a later paper by Pontecorvo on neutrino oscillations (1967) and by the anticipation of the solar neutrino problem. The article by V. Gribov and B. Pontecorvo where for the first time a solid theoretical formulation of neutrino oscillations (1969) was given is then considered. The general theory of neutrino mixing and oscillations and proposals of different experiments on the search for neutrino oscillations by S. M. Bilenky and B. Pontecorvo (1975–1989) are finally discussed in detail. The paper “Four-neutrino analysis of 1.5 km baseline reactor antineutrino oscillations” by S. K. Kang et al. describes sterile neutrinoswhichmight be discovered in 1.5 kmbaseline reactor neutrino experiments. Using recent data from RENO and Daya Bay, the authors performed an analysis of sterile neutrino search assuming a 3 + 1 scheme with 0.1 eV <