Neutral Higgs CP Violation at ${\mu }^{+}{\mu }^{-}$ colliders

CP violating asymmetries in both the production and the decays of $s$-channel neutral Higgs bosons at ${\mu }^{+}{\mu }^{-}$ colliders can be large. If the CP violation occurs in the muon-Higgs coupling, one observes a production asymmetry with transversely polarized ${\mu }^{+}{\mu }^{-}$ beams. Likewise if the CP violation occurs in the top-Higgs or $\tau$-Higgs coupling, one observes an azimuthal decay asymmetry in ${\mu }^{+}\mu -\to t\bar{t}$ (or ${\tau }^{+}{\tau }^{-}$). CP studies at such colliders allow a uniquely clean way of deducing the underlying CP phases; in turn these parameters would significantly improve our understanding of baryogenesis.