The $\gamma \gamma \to \gamma \gamma$ process in the standard and SUSY models at high energies

Abstract.

We study the helicity amplitudes of the process $\gamma \gamma \to \gamma \gamma$ at high energy, which in the standard and SUSY models first arise at the one-loop order. In the standard model (SM), the diagrams involve $W$, charged-quark, and lepton loops, while in SUSY, we also have contributions from chargino-, charged-sfermion, and Higgs-loop diagrams. The SUSY contributions are most important in the region above the threshold for producing the supersymmetric partners; there, they interfere most effectively with the primarily 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 various characteristics of a large set of observables are studied in detail.