LEADING QCD CORRECTIONS TO SCALAR QUARK CONTRIBUTIONS TO ELECTROWEAK PRECISION OBSERVABLES

In the supersymmetric extension of the standard model we derive the tw o-loop QCD corrections to the scalar quark contributions to the electr oweak precision observables entering via the rho parameter. A very com pact expression is derived for the gluon-exchange contribution. The co mplete analytic result for the gluino-exchange contribution is very le ngthy; we give expressions for several limiting cases that were derive d from the general result. The two-loop corrections, generally of the order of 10%-30% of the one-loop contributions, can be very significan t. Contrary to the standard model case, where the QCD corrections are negative and screen the one-loop value, the corresponding corrections in the supersymmetric case are in general positive, therefore increasi ng the sensitivity in the search for scalar quarks through their virtu al effects in high-precision electroweak observables. [S0556-2821(98)0 3405-5].