Killing vector fields on semi-Riemannian product manifolds

Abstract

Hano's theorem states that the space of Killing vector fields of a complete simply connected Riemannian manifold is isomorphic to the direct sum of the Killing vector fields of the factors in its de Rham decomposition. We prove a generalisation of this theorem to manifolds with indefinite metrics that requires an assumption on the factors, and show by example why this assumption is needed.

Dedicated to the Memory of Joseph A. Wolf