On-shell renormalization of the mixing matrices in Majorana neutrino theories
Abstract We generalize a recently proposed on-shell approach to renormalize the Cabibbo–Kobayashi–Maskawa quark-mixing matrix to the case of an extended leptonic sector that includes Dirac and Majorana neutrinos in the framework of the seesaw mechanism. An important property of this formulation is the gauge independence of both the renormalized and bare lepton mixing matrices. Also, the texture zero in the neutrino mass matrix is preserved.
Leptonic Flavor-changing Z0 Decays in SU(2)xU(1) Theories with Right- handed Neutrinos
We analyze possible lepton-flavor-violating decays of the $Z^0$ particle in a minimal extension of the Standard Model, in which one right-handed neutral field for each family has been introduced. Such rare leptonic decays are induced by Majorana neutrinos at the first electroweak loop level and are generally not suppressed by the ordinary "see-saw" mechanism. In particular, we find that experimental bounds on branching ratios of the order of $10^{-5}-10^{-6}$ attainable at $LEP$ may impose constraints on lepton-flavor-mixing parameters and the masses of the heavy Majorana neutrinos.
Neutrino counting at the Z-peak and right-handed neutrinos
Abstract We consider the implications of extending the minimal standard model, with n families of quarks and leptons, by introducing an arbitrary number of right-handed neutrinos, for neutrino-counting via the “invisible width” of the Z. It is shown that the effective number of neutrinos, 〈 n 〉, satisfies, the inequality 〈 n 〉 ⩽ n , where 〈 n 〉 is defined by Γ ( Z →neutrinos) ≡ 〈 n 〉 Γ 0 and Γ 0 is the standard width for one massless neutrino. Thus, in the case of three families, the neutrino-counting can give a result which is less than three, if there are right-handed neutrinos.