CP Violation in $\gamma \gamma \to t~\bar{t}$ within the Minimal   Supersymmetric Standard Model
  The complete analysis of the CP violation in the process $\gamma \gamma \to t \bar{t}$ in frame of the Minimal Supersymmetric Model(MSSM) is presented. The CP-odd observables for describing the CP violating effects in polarized and unpolarized photon collisions, are calculated. We investigate the possible CP violation sources induced by the complex soft breaking parameters and study the CP violating effects contributed by gluino, neutralino and chargino sectors appearing in the loop diagrams. We find that it is possible to observe the CP violation effects in top quark pair production via polarized and unpolarized photon fusions by using optimal observables and favorable parameters. 
Zhou Mian-Lai, Ma Wen-Gan, Han Liang, Jiang Yi and Zhou Hong