The γγ→γZ process at high energies and the search for virtual SUSY effects

We study the helicity amplitudes and the observables of the process γγ→γZ at high energy. As in the case of the γγ→γγ process studied before, the relevant diagrams in the standard model (SM) involve W, charged-quark, and lepton loops, while in SUSY we also have contributions from charginos and charged-sfermion or Higgs-loop diagrams. Above 250 GeV, the dominant SM amplitudes are themselves dominated by the W loop, and as for γγ→γγ, they are helicity conserving and almost purely imaginary. We discuss the complementary information provided by γγ→γZ for the identification of possible nonstandard effects. This process, together with γγ→γγ, should provide very useful information on the nature of possible new physics particles, above the threshold of their direct production. (orig.)