Resonant CP Violation in Higgs Production, Mixing and Decay

CP violation induced by resonant transitions of a scalar to a pseudoscalar intermediate state is analyzed within a gauge-invariant resummation approach based on the pinch technique. Necessary conditions governing the resonant enhancement of CP violation in transition amplitudes are derived. The results of this study are then applied to describe the indirect mixing of a CP-even Higgs scalar, $H$, with a CP-odd Higgs particle, $A$, in two-Higgs doublet models. CP violation through $HA$ mixing in high-energy $pp$, $e^+e^-$ and $\mu^+\mu^-$ scatterings are estimated to be fairly large for a natural choice of kinematic parameters. Low-energy constraints originating from experimental upper bounds on the neutron electric dipole model are implemented in this analysis.