Neutrino Oscillations by a Manifestly Coherent Mechanism and Massless vs. Massive Neutrinos

The neutrino oscillations in vacuum are derived in a manifestly coherent scheme. The mechanism is operative in a quantum field theoretical framework, justifying nevertheless a formal analogy with quantum mechanical two- (or more) level systems and their oscillatory behaviour. Both the flavour states and the massive states are eigenstates of certain Hamiltonians which, in special conditions, can be argued to share the same Hilbert space. In this scheme, flavour neutrinos are massless and play the role of asymptotic states for any interactions, including the weak interactions, while massive neutrinos are effective propagation states. The vacuum is interpreted as a medium, where the flavour neutrinos undergo coherent forward scatterings which modify their energy and mix their flavour. The treatment of matter conversion and MSW effect fits in naturally; the extension to other neutral particle oscillations, like $K_0-\bar K_0$, is straightforward. The scheme is eclectic insofar as it combines seamlessly quantum field theory and quantum mechanics.