Loop effects of exotic leptons on vector-boson pair production ate+e−colliders

We study the quantum effects of exotic heavy leptons on the production of two vector bosons in $e^{+}{e}^{-}$ annihilation. We present closed analytic expressions for vector-boson self-couplings and differential cross sections, within the framework of two favorable new-physics scenarios: (i) the fourth-generation Majorana-neutrino model and (ii) an $E_6$-inspired model with sequential mirror isodoublets. We constrain these models by requiring that their contributions to the oblique electroweak parameters be compatible with a recent global fit to high-precision data. We then systematically analyze the loop-induced deviations in the CERN LEP2 cross section of $e^{+}{e}^{-}\to W^{+}{W}^{-}$ predicted by the models thus confined.