Mixing transformations in QFT are non-trivial, since they are related with the unitary inequivalence between Fock spaces for definite mass and flavor fields. The question arises as to which of these two representations should be considered as physical. A clue to a solution has been recently provided in the context of particle decay.

The lifetime of a particle is usually considered as one of its intrinsic properties. For some particles such as the pion or muon, it can be estimated by knowing the interactions they experience. Conversely, other particles such as the electron or proton appear to be stable, at least in the Standard Model. Despite such a rooted belief, decay properties should not be regarded as fundamental, since they can be significantly manipulated by external influences. In this sense, one can affect the lifetime of pions or, even more strikingly, spoil the stability of protons, by exposing them to a sufficiently large acceleration. In this context, the inverse β-decay of uniformly accelerated protons was analyzed in both the laboratory frame (where the proton is accelerated) and the comoving frame (where the proton at rest interacts with a thermal bath due to Unruh effect). The equality between the two rates was exhibited as a theoretical proof of Unruh effect for the general covariance of QFT.

Nevertheless, in the above analysis neutrinos were simplistically considered as massless. Recently, this formalism was refined by embedding neutrino flavor mixing. This inevitably raised the aforementioned problem of which asymptotic representation to use (either flavor or mass states). Here, we show that the only scenario which allows us to: i) preserve the general covariance of QFT, ii) naturally describe neutrino oscillations, iii) take into account CP-violation is the one built upon flavor eigenstates. Phenomenological implications are investigated in connection with Katrin and Ptolemy experiments.