Flavor-changing decays of theZ0

Using the standard model of electroweak interactions, we compute the branching ratios for $Z^0\to q\overline{x}$, where $q$ and $x$ are quarks of different flavor. Such processes can be distinguished from the background only when $q$ is much more massive than $x$ (or vice versa); these rates are insignificant unless there are four (or more) generations of quarks. Since the results are then sensitive to the unknown mixing angles and masses of undiscovered quarks, we discuss these quantities briefly. We find that some values of these parameters lead to event rates that might be detectable in an $e^{+}{e}^{-}$ machine operating on the $Z^0$ resonance. The appendices contain our Feynman rules and technical details of the calculation.