Parametrizing and rephasing neutrino mixing

Neutrino mixing in Standard Model extensions, both renormalizable and effective, with arbitrary numbers of singlet and left-handed doublet neutrinos is investigated in a systematic fashion. The charged and neutral (Z-boson- and Higgs-boson-mediated) lepton currents are written under a general Majorana condition, and the independence of observables from the choice of condition, rephasing invariance, is studied. A parametrization of the neutrino mixing matrices in the doublet-singlet factorized form is developed. Its relationship with the seesaw mechanism is shown in the limit of small doublet-singlet mixing. The structure of the mixing matrices relevant to neutrino-oscillation experiments is explicated