EFFECTS OF HEAVY MAJORANA NEUTRINOS AND NEUTRAL VECTOR BOSONS ON ELECTROWEAK OBSERVABLES

Extensions of the standard model with extra neutral vector bosons predict additional fermions. In the minimal case, where the extended gauge group is contained in the unified group SO(10), one has one right-handed neutrino for each quark-lepton generation. For this theory we systematically study the effects of both, the mixing of neutral vector bosons and the neutrino mixing, on a variety of observables used for precision tests of the electroweak theory. In most quantities the effects of neutrino and vector boson mixing tend to compensate each other. In particular the shift in the invisible width of the Z boson may be positive or negative. The most stringent bounds follow from tests for universality of the charged current. A comparable sensitivity could be attained from a measurement of the left-right asymmetry and forward-backward asymmetries at the Z pole. We emphasize the importance of measuring tau-decays with improved accuracy.