NULL AND INFINITESIMAL ISOTROPY IN SEMI-RIEMANNIAN GEOMETRY

Null and infinitesimal isotropy are defined for semi-Riemannian manifo lds in a more general context. A theorem of Karcher is extended to sem i-Riemannian manifolds in a more general setting. Also, by using this theorem, a characterization of static blackhole metrics can be made as well as a characterization of Robertson-Walker metrics as Karcher mad e.