The gamma gamma -> gamma gamma process in the standard and SUSY models at high energies

We study the helicity amplitudes of the process gamma gamma --> gamma gamma at high energy, which in the standard and SUSY models first arise at the o ne-loop order. In the standard model (Sn I), the diagrams involve W, charge d-quark, and lepton loops, while in SUSY, we also have contributions from c hargino-, charged-sfermion, and Higgs-loop diagrams. The SUSY contributions are most important in the region above the threshold for producing the sup ersymmetric partners; there, they interfere most effectively with the prima rily imaginary SM amplitudes. Simple expressions for the relevant one-loop functions are given which provide a direct overview of the behaviour of the helicity amplitudes in the whole parameter space at high energies. The var ious characteristics of a large set of observables are studied in detail.