Neutrino self-polarization effect in matter

The quasi-classical theory of the spin light of neutrino ($SL\nu$) in background matter, accounting for the neutrino polarization, is developed. The neutrino transitions ${\nu }_L\to {\nu }_R$ and ${\nu }_R\to {\nu }_L$ rates in matter are calculated. It is shown that the $SL\nu$ in matter leads to the neutrino conversion from active ${\nu }_L$ to sterile ${\nu }_R$ states (neutrino self-polarization effect in matter).