Field mixing transformations are studied in quantum field theory and the
generator of the transformations is found to induce an SU(2) coherent structure
in the vacuum state, both for bosons and for fermions. The Fock space for mixed
fields is unitarily inequivalent to the Fock space of the unmixed fields in the
infinite volume limit. We study neutrino mixing and oscillations and find that
the oscillation amplitude is depressed by a factor which is momentum and mass
dependent. The usual formula is recovered in the relativistic limit.
Phenomenological features of the modified oscillation formula are discussed.
Finally, preliminary results of the Green's function formalism are presented.Comment: 14 pages, LaTeX. To appear in Proceedings of "Results and
Perspectives in Particle Physics", La Thuile, Aosta Valley, March 199
