Physical Higgs particles in the Minimal Supersymmetric Standard Model (MSSM) with explicit CP violation are CP mixed states. The decay of these Higgs particles can be analysed to study the CP properties of the MSSM. In the present work we consider the di-photon channel of the lightest neutral Higgs boson for this purpose. Compared to earlier studies on effects of scalar/pseudo-scalar mixing, our analysis also investigates the effect due to Higgs-sfermion-sfermion couplings along with that of mixing. We find that a light stop may have a strong impact on the width and Branching Ratio (BR) of the decay process H1 --> gamma.gamma, whereas other light sparticles have only little influence. In some regions of the MSSM parameter space with large CP-violating phase phi-mu ~ 90 deg a light (~ 200 GeV) stop can change the di-photon BR by more than 50 % compared to the case with heavy (~ 1 TeV) stop and otherwise same MSSM parameters.
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