Precision observables in SU(2) x U(1) models with an additional Higgs triplet

Electroweak precision observables are calculated at complete one-loop order in the extension of the standard model by an extra Higgs triplet, where the ρ-parameter can be different from unity already at the tree level. One additional data point is required for fixing the input parameters. In the on-shell renormalization scheme the leptonic mixing angle sin 2θe at the Z peak is chosen, together with the conventional input α, MZ, Gμ, mt. The calculated observables depend on the mass of the doublet Higgs boson H0 and on the masses of the extra non-standard Higgs bosons as free parameters. The predictions of the standard model and the triplet model coincide for all observables in the experimental range of the top mass. In the triplet model, all observables which show a dependence on the doublet Higgs mass MH0 are consistent with a low value of MH0. (orig.)