RESONANT CP VIOLATION INDUCED BY PARTICLE MIXING IN TRANSITION AMPLITUDES

We analyze CP violation in resonant transitions involving scalar as we ll as fermionic intermediate states, using a gauge-invariant resummati on approach implemented by the pinch technique. We derive the necessar y conditions for resonantly enhanced CP violation induced by particle mixing, by paying special attention to CPT invariance, and apply the r esults of our analysis to two representative new-physics scenarios: (i ) the indirect mixing of a CP-even Higgs scalar with a CP-odd Higgs pa rticle in two-Higgs doublet models and (ii) the CP-asymmetric mixing b etween the top-quark and a new heavy up-type quark, t', in mirror ferm ion models. Furthermore, we explicitly demonstrate the equivalence of our scattering-amplitude formalism with that based on the effective Ha miltonian and discuss the possibility of maximal CP violation in the l imiting case of two degenerate particles. (C) 1997 Elsevier Science B. V. PACS: 11.30.Er; 13.10.+q; 14.80.Bn; 14.80.Cp.