Green's Function in Weak Interactions (in Matter) and Impossibility of   Realizing the MSW Effect
  It is shown that the equation for Green's function of fermions (neutrinos) with weak interactions (in matter) coincides with the equation for Green's function of fermions in vacuum. This result is a consequence of the fact that the right components of fermions do not participate in weak interactions. As a result we come to a conclusion: the mechanism of resonance enhancement of neutrino oscillations in matter (i.e. MSW effect) cannot exist. 
Kh.M. Beshtoev