Production of Light Fermion-Antifermion Pairs in $\gamma \gamma$ Collisions

The $O(\alpha)$ corrections to $\gamma\gamma --> f \bar f$ in the Standard Model are calculated for arbitrary, light fermions $f$. The relevant analytical results are listed in a form that is appropriate for practical applications, and numerical results for integrated cross sections are discussed. The corresponding QED corrections are generally of the order of some per mille for arbitrary energies. The weak corrections to $\gamma\gamma --> e^-e^+$ are negligible below the electroweak scale, reach the per-cent level at a few hundred GeV and grow to about -10% at 2TeV. The weak corrections to $u \bar u$ and $d \bar d$ production have a shape similar to the one for $e^-e^+$, but they are larger by factors $\sim 1.4$ and $\sim 3$, respectively.