On Lorentz dynamics : From group actions to warped products via   homogeneous spaces
  We show a geometric rigidity of isometric actions of non compact (semisimple) Lie groups on Lorentz manifolds. Namely, we show that the manifold has a warped product structure of a Lorentz manifold with constant curvature by a Riemannian manifold. 
Abdelouahab Arouche (LATN-USTHB), Mohamed Deffaf (LATN-USTHB),   Abdelghani Zeghib (UMPA-ENSL)