Diffusion des ondes par une violation de la causalité

We introduce a class of four dimensional Lorentzian manifolds with closed curves of null type or timelike. We investigate some global problems for the wave equation: global Cauchy problem and asymptotic completeness of the wave operators for the chronological but non-causal metrics; uniqueness of solution with data on a changing type hypersurface; existence of resonant states; scattering by a violation of the chronology; poles of the scattering matrix.