SUPERSYMMETRIC CONTRIBUTIONS TO ELECTROWEAK PRECISION OBSERVABLES - QCD CORRECTIONS

We calculate the two-loop QCD correction to the scalar quark contribut ions to the electroweak gauge-boson self-energies at zero momentum tra nsfer in the supersymmetric extension of the standard model (SM) and d erive the associated Omicron (alpha(s)) correction to the rho paramete r. The two-loop corrections modify the one-loop contribution by up to 30%; the gluino decouples for large masses. Contrary to the SM case wh ere the QCD corrections are negative and screen the one-loop value, th e corresponding corrections in the supersymmetric case are in general positive, increasing the sensitivity in the search for scalar quarks t hrough their virtual effects in high-precision electroweak observables .