Insight into neutrino mass phenomenology by exploring the non-relativistic regime in quantum field theory

We present a novel formulation, based on quantum field theory, for neutrino oscillation phenomenology that can be applied to non-relativistic and relativistic energies for neutrinos. The formulation is constructed as a time evolution of a lepton family number operator. At time $t=0$, we assign either a Dirac or Majorana mass to the neutrino. Then, the time evolution of the lepton family number operator becomes dependent on the mass and new features appear. We show in the non-relativistic regime, by taking the expectation value of the lepton number operator, the absolute mass hierarchy and the type of neutrino mass are distinguishable.