Higgs-Z mixing and resonant CP violation at μ+μ-colliders

A μ+μ- collider is an appealing machine to probe resonant CP-violating transitions between a CP-even Higgs particle and the Ζ boson or between Higgs scalars with different CP quantum numbers. The size of the CP-violating effects is estimated by using an observable of CP assymetry based on longitudinally polarized muons. These phenomena are studied within a manifestly gauge-invariant approach implemented by the pinch technique, which respects the discrete symmetries of the classical Langrangian and is therefore free from CP-odd gauge artifacts. The CP invariance of an extended Higgs sector motivated by E6 supersymmetric models is assumed to be broken by the presence of heavy Majorana fermions. CP violation originating from Higgs-Ζ 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. (UK)