The coupled Dirac equations for solar e- and μ-neutrinos are solved
in the presence of a small uniform interaction of the e-neutrinos with
matter (the Sun). It is shown that the interaction leads to an increase
of the amplitude of the neutrinos oscillations and a decrease of the lo-
calization probability of the e-neutrinos. However, the strength of this
interaction is insufficient to explain the magnitude of the discrepancy
between the solar neutrino flux and the neutrino flux measured on the
Earth. An alternative interpretation related to a possible superfluid
neutrino state is advanced, which may throw some light on the solar
neutrino problem.