Dark CP-violation through the $Z$-portal

Despite great agreement with experiment, the Standard Model (SM) of particle physics lacks a viable Dark Matter (DM) candidate and sufficient amount of CP-violation to account for the observed baryon excess in the universe. Non-minimal Higgs frameworks are economic extensions of the SM which could remedy these shortcomings. Within the framework of a three Higgs doublet model, we introduce an extended dark sector which accommodates both DM and CP-violation. Such dark sources of CP-violation do not contribute to the Electric Dipole Moments and are therefore unconstrained. We present a novel mechanism in which the CP-violating dark particles only interact with the SM through the gauge bosons, primarily the $Z$ boson. Such $Z$-portal dark CP violation is realised in the regions of the parameter space where Higgs-mediated (co)annihilation processes are sub-dominant and have negligible contributions to the DM relic density. We show that such $Z$-portal CP violating DM can still thermalise and satisfy all experimental and observational bounds and discuss the implications of such phenomena for electroweak baryogenesis.