Theory of neutrino detection: flavor oscillations and weak values

We revisit the theory of neutrino oscillations and describe it through the formalism of weak measurements with postselection. It is well understood that due to the large momentum uncertainty in detection, there is no collapse of the neutrino wavefunction in the momentum or energy basis, and the mass eigenstates are detected coherently. Here we show that postselection, which projects the system to a final flavor state, deforms the system wavefunction in such a way that the momentum detected is not the expectation value of the neutrino mass eigenstates momenta, but the corresponding weak value. We use the weak values to describe the intermediate state in the oscillation process, avoiding problems in defining probability currents for particle states with mass superposition.