Solar neutrinos and grand unification

Abstract

We consider the Grand Unification (GU) scenario for neutrino masses which is based on the see-saw mechanism with the mass of the heaviest right handed (RH) neutrino at the GU-scale: $M_3\sim {\Lambda }_{GU}$, and on the quark-lepton symmetry for fermions from the third generation. The scenario predicts for the light neutrinos: $m_3\sim (2-4)\cdot 10^{-3}$ eV and $m_2\sim (0.3-3)\cdot 10^{-5}$ eV (in the case of a linear mass hierarchy of the RH neutrinos or/and in presence of the Planck scale suppressed non-renormalizable operators). It also predicts large ${\nu }_e-{\nu }_{\mu }$ mixing: ${\sin }^{2}2{\theta }_{e\mu }\stackrel{{}_{>}}{{}_{\sim }}0.2$. In this scenario the solar neutrinos (${\nu }_{\odot }$) undergo both the \nue $\to$ \nutau resonance conversion in the Sun and substantial \nue $\to$ \numu vacuum oscillations on the way from the Sun to the Earth. The interplay of both effects enlarges the range of neutrino parameters which solve the ${\nu }_{\odot }$-problem. In particular, ${\nu }_e-{\nu }_{\tau }$ mixing angle can be as small as the corresponding quark mixing: ${\sin }^{2}2{\theta }_{e\tau }\ge (2-5)\cdot 10^{-4}$. The scenario predicts peculiar (oscillatory) distortion of the boron neutrino energy spectrum and seasonal variations of signals. Manifestations of these effects in the Super-Kamiokande and SNO experiments are studied.

Comments: 36 pages, LaTeX, includes 14 figures, revised and expanded