Single leptoquark production ate+e−andγγcolliders

We consider single production of leptoquarks (LQ's) at $e^{+}{e}^{-}$ and $\gamma \gamma$ colliders, for two values of the center-of-mass energy: $\sqrt{s}=500\mathrm{}$ GeV and 1 TeV. We find that LQ's which couple within the first generation are observable for LQ masses almost up to the kinematic limit, both at $e^{+}{e}^{-}$ and $\gamma \gamma$ colliders, for an LQ coupling strength equal to ${\alpha }_{\mathrm{em}}$. The cross sections for single production of second- and third-generation LQ's at $e^{+}{e}^{-}$ colliders are too small to be observable. In $\gamma \gamma$ collisions, on the other hand, second-generation LQ's with masses much larger than $\frac{\sqrt{s}}{2}$ can be detected. However, third-generation LQ's can be seen at $\gamma \gamma$ colliders only for masses at most $\sim \frac{\sqrt{s}}{2}$, making their observation more probable via the pair production mechanism.