How Do Neutrinos Propagate?: Wave-Packet Treatment of Neutrino Oscillation

The wave-packet treatment of neutrino oscillation developed previously is extended to the case in which momentum distribution functions are taken to have a Gaussian form with both central values and dispersions depending on the mass eigenstates of the neutrinos. It is shown that the velocities of the neutrino wave packets do not in general agree with what one would expect classically but that relativistic neutrinos emitted from pions nevertheless do follow, to a good approximation, the classical trajectory. It is further pointed out that the conventional equal-energy (equal-momentum) prescription for neutrino oscillation seems appropriate to approximately describe oscillation experiments that involve something corresponding to time- (space-) integration or averaging.