Franco Tricerri

Lorentz manifolds modelled on a Lorentz symmetric space

Abstract We give examples of Lorentz manifolds modelled on an indecomposable Lorentz symmetric space which are geodesically complete and not locally homogeneous.

Curvature-orbits and locally homogeneous riemannian manifolds

We prove that it is possible to associate to each infinitesimal model on a Euclidean vector space V a locally homogeneous Riemannian manifold. As an application, we characterize, in the space of the algebraic curvature tensors on V, the orbits which can occur for locally homogeneous Riemannian manifolds.