Flavor-changing decays of theZ0and leptoquarks

Many extensions of the standard model, e.g., certain composite models and some superstring-"inspired" ${\mathrm{E}}_6$ models, contain new scalar matter fields which couple to both quarks and leptons, i.e., leptoquarks. We consider leptonic flavor-changing decays of the $Z^0$, e.g., $Z^0\to {\mu }^{+}{\tau }^{-}$, due to one-loop diagrams involving such leptoquarks. We find branching ratios which are at most ≈${10}^{-7\mathrm{}}$, even assuming generous values for unknown Yukawa couplings.