We consider neutrino oscillations in a medium in which scattering processes
are blind to the neutrino flavour. We present an analytical derivation of the
synchronised behaviour obtained in the limit where the average scattering rate
is much larger than the oscillation frequency. We also examine MSW transitions
in these circumstances, and show that a sharpening of the transition can
result.Comment: 8 pages, 3 figures, accepted for publication in Phys. Lett.
