Neutrino mixing and leptonic $CP$ phase in neutrino oscillations

Oscillations of the Dirac neutrinos of three generations in vacuum are considered with allowance made for the effect of the $CP$-violating leptonic phase (analogue of the quark $CP$ phase) in the lepton mixing matrix. The general formulas for the probabilities of neutrino transition from one sort to another in oscillations are obtained as functions of three mixing angles and the $CP$ phase. It is found that the leptonic $CP$ phase can, in principle, be reconstructed by measuring the oscillation-averaged probabilities of neutrino transition from one sort to another. The manifestation of the $CP$ phase as a deviation of the probabilities of direct processes from those of inverse processes is an effect that is practically unobservable as yet.