Enhancement of CP-violating phenomena at tree level due to heavy quark propagator singularities

We discuss new interesting CP-violating phenomena in scattering processes resulting from heavy quarks with masses larger than the W-mass (m _q >M _W ). Such a situation is connected with a singularity in the heavy quark propagator which, properly regularized, gives rise to measurable CP-odd effects. The observability of these CP-odd signals in the most representative Kobayashi-Maskawa (KM) models (like fourth generation model, left-right symmetric model and two Higgs doublet model) is investigated. We find that the necessary conditions for measurable CP-asymmetries imply the enlargement of the Standard Model (SM) in the generations of quarks. In addition a significant mixing between the fourth and the other generations is required.