Neutrino 2012: Outlook - theory

Abstract

Ongoing developments in theory and phenomenology are related to the measured large value of 1-3 mixing and indications of significant deviation of the 2-3 mixing from maximal one. "Race" for the mass hierarchy has started and there is good chance that multi-megaton scale atmospheric neutrino detectors with low threshold (e.g. PINGU) will establish the type of hierarchy. Two IceCube candidates of the PeV cosmic neutrinos if confirmed, is the beginning of new era of high energy neutrino astronomy. Accumulation of data on solar neutrinos (energy spectrum, D-N asymmetry, value of $\Delta m^2_{21}$) may uncover some new physics. The Tri-bimaximal mixing is disfavored and the existing discrete symmetry paradigm may change. The confirmed QLC prediction, $\theta_{13} \approx \theta_{C}/\sqrt{2}$, testifies for GUT, seesaw and some symmetry at very high scales. However, the same value of 1-3 mixing can be obtained in various ways which have different implications. The situation in lepton sector changes from special (with specific neutrino symmetries, etc.) to normal, closer to that in the quark sector. Sterile neutrinos are challenge for neutrino physics but also opportunity with many interesting phenomenological consequences. Further studies of possible connections between neutrinos and the dark sector of the Universe may lead to breakthrough both in particle physics and cosmology.