Neutrino Flavor Mixing and Oscillations in Field Theory
  The Lagrangian that is normally associated with Dirac neutrinos is analyzed in a complete and simple way through field theory. It is found that the elements of the neutrino mass matrix are field strength renormalization constants and that the flavor fields can be directly applied to the one-particle energy states through these rescaling factors. Moreover this Lagrangian describes neutrinos which are in a state of mixed flavor at any space-time point and therefore does not describe the phenomenology of neutrino oscillations properly, except in the ultra-relativistic limit where such a description is possible. 
E. Sassaroli