RADIATIVE-CORRECTIONS TO GAMMA-GAMMA-]T(T)OVER-BAR IN THE ELECTROWEAKSTANDARD MODEL

The cross section for gamma gamma --> t (t) over bar with arbitrary po larized photons is calculated within the electroweak standard model in cluding the complete virtual and soft-photonic O(alpha) corrections. W e present a detailed numerical discussion of the radiative corrections with particular emphasis on the purely weak corrections. These are us ually 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 suc h as the running of cr or the rho parameter. Apart from the energy reg ion around the Higgs resonance (gamma gamma --> H --> t (t) over bar the weak corrections are widely independent of the Higgs-boson mass.