Resonant CP-Violating Scalar--Pseudoscalar Transitions at mu+ mu-   Colliders
  A mu+ mu- collider is an appealing machine to probe resonant CP-violating transitions of a CP-even Higgs particle into the Z boson or into another CP-odd Higgs scalar. These phenomena are studied within a manifestly gauge-invariant approach implemented by the pinch technique. The CP invariance of an extended Higgs sector motivated by supersymmetric E_6 models is assumed to be broken radiatively by the presence of heavy Majorana fermions. CP violation originating from Higgs-Z mixing is found to be very modest, whereas CP-number violating transitions involving Higgs scalars only can be resonantly enhanced up to order of unity. 
Apostolos Pilaftsis