Neutrino mixing and general covariance in the inverse $β$ decay

We review recent developments on the role of neutrino mixing in the inverse β decay of accelerated protons. We show that calculations in the inertial and comoving frames agree -- thus preserving general covariance -- only when taking neutrino asymptotic states to be flavor (rather than mass) eigenstates. Our conclusions are valid in the approximation in which Pontecorvo states are correctly representing neutrino flavor states. We speculate about the general case involving exact flavor states and finally comment on other approaches recently appeared in literature.