EFFECTIVE POTENTIAL METHODS AND THE HIGGS MASS-SPECTRUM IN THE MSSM

We generalize the analytical expressions for the two-loop leading-log neutral Higgs boson masses and mixing angles to the case of general le ft- and right-handed soft supersymmetry breaking stop and sbottom mass es and left-right mixing mass parameters (m(Q), m(U), m(D), A(t), A(b) ) This generalization is essential for the computation of Higgs masses and couplings in the presence of light stops. At high scales we use t he minimal supersymmetric standard model effective potential, while at low scales we consider the two-Higgs doublet model (renormalization g roup improved) effective potential, with general matching conditions a t the thresholds where the squarks decouple. We define physical (pole) masses for the top quark, by including QCD self-energies, and for the neutral Higgs bosons, by including the leading one-loop electroweak s elf-energies where the top/stop and bottom/sbottom sectors propagate. For m(Q) = m(U) = m(D) and moderate left-right mixing mass parameters, for which the mass expansion in terms of renormalizable Higgs quartic couplings is reliable, we find excellent agreement with previously ob tained results.