Matter Induced Neutrino Decay: New Candidate for the Solution to the Solar Neutrino Problrm

Effects of the dense matter can induce the neutrino decay even if neutrinos are stable in vacuum. This is due to coherent interactions with matter which lead to energy level-splitting between the neutrino and antineutrino states and thereby provide available phase space for the majoron emission. We show that the matter induced decay can be a plausible candidate for the explanation of solar neutrino deficit, provided that there exist new flavour-changing weak range interactions of neutrino with matter constituents, and constant of $\tau$-neutrino coupling to the majoron is sufficiently large. This mechanism naturally implies the hierarchy between the ratios Z=(measured signal)/(SSM expectation) for Ga-Ge, nu_e-e scattering and Cl-Ar experiments - Z_{GA}>Z_{K}>Z_{Cl}. The important feature of the matter induced decay is the prediction of solar antineutrino flux with substantially degraded energy spectrum compared to solar neutrinos. This scenario can be unambiguously tested by future solar neutrino detectors BOREXINO/BOREX and SNO.