Two-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 (mh), in the minimal and non-minimal (including a gauge singlet) supersymmetric standard model, when the scale of supersymmetry breaking (MSUSY) is larger than the electroweak 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 correaction 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 (mt), and MSUSY. These theoretical bounds, along with future experimental bounds on mt and mh, could be used to push MSUSY towards higher scales. (orig.)