Effects of new physics to the the $\rho$--parameter in the supersymmetric standard model

Abstract

The contribution to the $\rho$--parameter of the quark--Higgs sector of the supersymmetric standard model is computed non--perturbatively using the large--$\nf$ expansion for the case tan$\beta$=0. An explicit formula is found for the $\rho$--parameter which is ill-defined unless the triviality cutoff is taken into account. The cutoff dependence of the $\rho$--parameter is found to be large if and only if the top mass is larger than $2v$ so that the cutoff scale is of the order of the electroweak scale. These non--universal effects are the reflections at low energies of the physics beyond the supersymmetric standard model. By also considering the effects of the soft--breaking terms, cutoff effects in both decoupling and non--decoupling effects are analyzed.