Actions of semisimple Lie groups preserving a degenerate Riemannian metric

2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/142378We prove a rigidity of the lightcone in Minkowski space. It is essentially the unique space endowed with a degenerate Riemannian metric, of lightlike type, and supporting an isometric non-proper action of a semi-simple group.22 pagesDifferential GeometryDynamical Systems53C50, 53C30, 53C24Actions of semisimple Lie groups preserving a degenerate Riemannian metrictext