FERMION LOCALIZATION AND CAUSALITY

The velocity of a fermion (neutrino) propagation from its source to its detector is investigated. It is shown that a simple approach to the problem in terms of the quantum packet spreading (Hegerfeldt et al.) is not applicable because the fermion cannot be localized in a bounded space region. Another approach is elaborated which uses relativistic quantum field description of the fermion source and detector. It is demonstrated that the velocity of the fermion propagation does not exceed the light velocity c within the precision of the source and detector localization.