Production of a single heavy quark ine+e−collisions

Cross sections for the flavor-changing neutral transition $e^{+}{e}^{-}\to \overline{t}c$ are calculated in the standard model with three generations, and found to be unmeasureable; $e^{+}{e}^{-}\to \overline{b}s$ is a few orders of magnitude larger. Experimentalists should nevertheless look for these processes since an increase in the number of generations, strong-interaction effects, and mainly nonstandard models may lead to observable rates. $Z^0$ decays into a single heavy quark plus a light one are also briefly discussed.