Gluino-induced effects and precision measurements at the CERNe+e−collider LEP

A gauge-invariant subset of minimal supersymmetry, driven by the quark-squark-gluino Lagrangian, is our concern in the context of precision measurements at the CERN $e^{+}{e}^{-}$ collider LEP on $Z$ decays. Shifts of the parameter $R=\frac{{\Gamma }_{\mathrm{had}}}{{\Gamma }_{l\overline{l}}}$, a precisely measured top-quark-free observable at LEP, due to vertex corrections induced by the above interaction, have been evaluated for different regions of the supersymmetric parameter space. Owing mainly to the stringent bounds on the masses of the squarks and the gluino from the direct search at the Fermilab Tevatron, the effects are not too large to cast an observable impact at the present stage of LEP precision.