Improved supersymmetric QCD corrections to Higgs boson decays into quarks and squarks - art. no. 055006

We improve the calculation of the supersymmetric O(alpha(s)) QCD correction s to the decays of Higgs bosons into quarks and squarks in the minimal supe rsymmetric standard model. In the on-shell renormalization scheme these cor rections can be very large, which makes the perturbative expansion unreliab le. This is especially serious for decays into bottom quarks and squarks fo r large tan beta. Their corrected widths can even become negative. We show that this problem can be solved by a careful choice of the tree-level Higgs boson couplings to quarks and squarks, in terms of the QCD and SUSY QCD ru nning quark masses, running trilinear couplings A(q), and on-shell left-rig ht mixing angles of squarks. We also present numerical results for the corr ected partial decay widths for the large tan beta case.