Radiative corrections in unconstrained SU(2) x U(1) models and the top-mass problem

We discuss the structure of SU(2)xU(1) radiative corrections in the general case where no global SU(2)LxSU(2)R symmetry is present. We argue that the electroweak theory, equipped with a non-standard but otherwise general Higgs sector, allows for values of mt significatively larger than the commonly accepted present upper bounds. This result does not rely on fine-tuned cancellations among different contributions to the ρ-parameter, but is a general consequence of the one-loop structure of models of this kind, and holds independently of the sign of ρ - 1. Our conclusions are reinforced by a full and detailed analysis of the simplest of such extensions of the minimal theory. We conclude that if in the near future the top quark is not found in the mass range suggested by the present analysis, this could be interpreted as a strong indication that new scalars in higher-dimensional representations contribute to drive the breaking of the electroweak gauge symmetry. (orig.)