Measuring the Higgs CP Property through Top Quark Pair Production at   Photon Linear Colliders
  We present a model-independent study of the effects of a neutral Higgs boson without definite CP-parity in the process $\gamma\gamma \to t\bar{t}$ around the mass pole of the Higgs boson. Near the resonance pole, the interference between the Higgs-exchange and the continuum amplitudes can be sizable if the photon beams are polarized and helicities of the top and anti-top quarks are measured. Study of these interference effects enables one to determine the CP property of the Higgs boson completely. An example of the complete determination is demonstrated in the context of the minimal supersymmetric standard model. 
Eri Asakawa, S.Y. Choi, Kaoru Hagiwara, Jae Sik Lee