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The gamma gamma to gamma Z process at high energies and the search for virtual SUSY effects

We study the helicity amplitudes and the observables of the process $γγ\to γZ$ at high energy. As in the case of the $γγ\to γγ$ 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 chargino, and charged sfermion or Higgs loop diagrams. Above 250 GeV, the dominant SM amplitudes are themselves dominated by the $W$ loop, and as for $γγ\to γγ$, they are helicity conserving and almost purely imaginary. We discuss the complementary information provided by $γγ\to γZ$ for the identification of possible non standard effects. This process, together with $γγ\to γγ$, should provide very useful information on the nature of possible new physics particles, above the threshold of their direct production.