Neutrino mass and new physics

Abstract

Reconstruction of the neutrino mass and flavor spectrum is described. Essentially two processes are relevant for interpretation of the neutrino results which were used in determination of neutrino parameters: oscillations (averaged and non-averaged) in vacuum and matter and the adiabatic flavor conversion in matter (the MSW-effect). Detailed physics picture of these processes is elaborated and their realizations in solar and atmospheric neutrinos as well as in K2K, KamLAND and MINOS experiments are described. Important bounds have been obtained from neutrinoless double beta decay and cosmology. Implications of the obtained results to fundamental physics are discussed. Among various mechanisms for small neutrino masses we consider the seesaw (which has the highest priority) and overlap suppression in extra dimensions. The observed pattern on neutrino mixing may testify for existence of new symmetries of nature. One of the key issues on the way to underlying physics is comparison of the quarks and lepton masses and mixing. In this connections concepts of quark-lepton symmetry and unification, quark-lepton universality and quark-lepton complementarity are described. © 2006 IOP Publishing Ltd.