Indirect Signatures of CP Violation in the Processes $\gamma \gamma \to \gamma \gamma$, $\gamma Z$, and $ZZ$
This paper studies the utility of the processes $\gamma \gamma \to \gamma \gamma$, $\gamma Z$, and $ZZ$ in searching for sources of CP violation arising from energy scales beyond the production thresholds of planned future colliders. In the context of an effective Lagrangian approach we consider the most general set of CP odd SU(2) $\times$ U(1) operators that give rise to genuinely quartic gauge boson couplings which can be probed in $2 \to 2$ scattering processes at a $\gamma \gamma $ collider. We study each process in detail, emphasizing the complementary information that is obtained by varying the initial beam polarizations. Finally, we compare our results to other constraints in the literature on CP odd gauge boson interactions and quartic gauge boson couplings; the search reaches obtained here are typically stronger and nicely complement previous studies which have focused primarily on $W$ boson, top quark, or Higgs production.