Neutrino oscillations in gravitational and cosmological backgrounds
  We use the eikonal approximation in order to calculate the additional phase
shift between two neutrino mass eigenstates during their propagation in a
background of gravitational wave or scalar perturbations in the flat and the
FRW spacetime metric. We comment on the dependence of the results on the
characteristics of the perturbations, give some order-of-magnitude estimates,
and find that, although small, the resulting phase difference persists for
large redshifts, up to the validity of our approximations.
