2-LOOP RADIATIVE-CORRECTIONS TO THE MASS OF THE LIGHTEST HIGGS BOSON IN SUPERSYMMETRIC STANDARD MODELS

We compute the two-loop corrections to the mass of the lightest Higgs boson (m(h)), in the minimal and non-minimal (including a gauge singlet) supersymmetric standard model, when the scale of supersymmetry breaking (M(SUSY) is larger than the electro-weak scale. We use the effective potential in the leading logarithm approximation and renormalization group techniques. We find that, even in cases where the one-loop correction is larger than the tree-level mass, the two-loop correction stays within a few percent. We present, for minimal and non-minimal models, two-loop upper bounds, which depend on the top-quark mass (m(t)), and M(SUSY). These theoretical bounds, along with future experimental bounds on m(t) and m(h), could be used to push M(SUSY) towards higher scales.