Universality-breaking effects in leptonic Z decays.

Abstract

We analyze the possibility of universality violation in diagonal leptonic decays of the Z boson, in the context of interfamily ``seesaw'' models. In a minimal extension of the standard model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the current experiments at the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ collider LEP.