Classification of the Ricci tensor in space-times admitting a four-parameter group of motions acting on non-null hypersurfaces

Abstract

The Plebanski type of the Ricci tensor for all metrics admitting a four-parameter group of motions acting on non-null (space-like or time-like) hypersurfaces is determined by using the Newman-Penrose formalism and a classification method due to Ludwig and Scanlan. For each metric, all possible degeneracies of the Plebanski type are considered.