The exact parametrization of the neutrino mixing

We discuss the propagation and the flavour mixing of neutrinos in the context of the Quantum Field Theory. We propose an exact parametrization of the neutrino mixing matrix and its transformation in a simpler form which accounts for a small $\nu_e - \nu_\mu$ and a large $\nu_\mu - \nu_\tau$ mixing. Finally, we comment the differences between the charged quark and neutral lepton sector and consider the physical situations that require this approach.