Scalar top production in e+e- annihilation

We discuss the pair production of light scalar top quarks in e+e- annihilation. The lighter mass eigenstate t1 is a mixture of SU(2) doublet and singlet t states and can have a vanishing coupling to the Z boson. We show that the present data on the total decay width of the Z0 can put a bound on the t1 mass for some values of the mixing angle, but even existing dedicated search for squarks leaves a large portion of the parameter space unconstrained. We include both initial-state QED and final-state QCD corrections in our results for the cross section; even quite far away from the threshold the total corrections can lie between -15% and +70%. (orig.)