CP-violating chargino contributions to the Higgs coupling to photon pairs in the decoupling regime of the Higgs sector

In most supersymmetric theories, charginos X̃_1,2^± belong to the class of the lightest supersymmetric particles and the couplings of Higgs bosons to charginos are in general complex so that the CP-violating chargino contributions to the loop-induced coupling of the lightest Higgs boson to two photons can be sizable even in the decoupling limit of large pseudoscalar mass m_A with only the lightest Higgs boson kinematically accessible at future high energy colliders. We introduce a specific benchmark scenario of CP violation consistent with the electric dipole moment constraints and with a commonly accepted baryogenesis mechanism in the minimal supersymmetric standard model. Based on the benchmark scenario of CP violation, we demonstrate that the fusion of the lightest Higgs boson in linearly polarized photon-photon collisions can allow us to confirm the existence of the CP-violating chargino contributions even in the decoupling regime of the Higgs sector for nearly degenerate SU(2) gaugino and Higgsino mass parameters of about the electroweak scale.