The cross section for γγ→tt¯ with arbitrary polarized photons is calculated within the electroweak standard model including the complete virtual and soft-photonic O(α) corrections. We present a detailed numerical discussion of the radiative corrections with particular emphasis on the purely weak corrections. These are usually of the order of 1–10% for energies up to 1 TeV. For unpolarized or equally polarized photons they reach almost 10% close to threshold. The large corrections cannot be traced back to a universal origin such as the running of α or the ρ parameter. Apart from the energy region around the Higgs resonance (γγ→${\mathit{H}}^{\mathrm{*}}$→tt¯) the weak corrections are widely independent of the Higgs-boson mass. © 1995 The American Physical Society.

• Received 26 July 1995

DOI:https://doi.org/10.1103/PhysRevD.53.44