Phenomenology of neutral heavy leptons

Abstract

We continue our previous work on the flavor-conserving leptonic decays of the $Z$ boson with neutral heavy leptons (NHL's) in the loops by considering box, vertex, and self-energy diagrams for the muon decay. By inclusion of these loops (they contribute to the input parameter ${M}_{W})$, we can probe the full parameter space spanned by the so-called flavor-conserving mixing parameters ${\mathrm{ee}}_{\mathrm{mix}},\ensuremath{\mu}{\ensuremath{\mu}}_{\mathrm{mix}},\ensuremath{\tau}{\ensuremath{\tau}}_{\mathrm{mix}}.$ We show that only two diagrams from each class (box, vertex, and self-energy) are important; further, after renormalization only two box diagrams ``survive'' as dominant. We compare the results of our analysis with the existing work in this field and conclude that flavor-conserving decays have certain advantages over traditionally considered flavor-violating ones.