Parametrizing and rephasing neutrino mixing

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