EINSTEIN SPACES WITH A CONFORMAL GROUP

Abstract. The pseudo-Riemannian Einstein spaces with a (local or global) conformal group of strictly positive dimension can be classified. In this ar-ticle we give a straightforward and systematic proof. As a common gen-eralization, this includes the global theorem of Yano and Nagano in the Riemannian case (1959, published in the Annals of Mathematics) and a pseudo-Riemannian analogue proved by Kerckhove in his 1988 thesis under Professor K.Nomizu. We extend and unify the previous results in the case of an indefinite metric by analogy with the case of a positive definite metric. 1. Introduction an