CONFRONTING LEFT-RIGHT SYMMETRIC MODELS WITH ELECTROWEAK PRECISION DATA AT THE Z PEAK

In view of the recent and future electroweak precision data accumulated at LEP and SLC, we systematically analyze possible new physics effects that may occur in the leptonic sector within the context of $SU(2)_R \times SU(2)_L \times U(1)_{B-L}$ theories. It is shown that nonobservation of flavour-violating $Z$-boson decays, lepton universality in the decays $Z\to l\bar{l}$, and universality of lepton asymmetries at the $Z$ peak form a set of complementary observables, yielding severe constraints on the parameter space of these theories. Contributions of new-physics effects to $R_b=\Gamma(Z\to b\bar{b})/\Gamma(Z\to \mbox{hadrons})$ are found to give interesting mass relations for the flavour-changing Higgs scalars present in these models.