Constraining new models with precision electroweak data

Electroweak precision data have been extensively used to constrain models containing physics beyond that of the Standard Model (SM). When the model contains Higgs scalars in representations other than singlets or doublets, and hence rho not equal 1 at tree-level, a correct renormalization scheme requires more inputs than the three commonly used for the SM case. In such cases, the one-loop electroweak results cannot be split into a SM contribution plus a piece which vanishes as the scale of new physics becomes much larger than M-W. We illustrate our results by presenting the dependence of MW on the top-quark mass in a model with a Higgs triplet and in the SU(2)(L) x SU(2)(R) left-right symmetric model. In these models, the allowed range for the lightest neutral Higgs mass can be as large as a few TeV.