  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.
