Canonical variation of a Lorentzian metric

Abstract

Given a Lorentzian manifold $(M,g_L)$ and a timelike unitary vector field $E$, we can construct the Riemannian metric $g_R=g_L+2\omega\otimes\omega$, being $\omega$ the metrically equivalent one form to $E$. We relate the curvature of both metrics, especially in the case of $E$ being Killing or closed, and we use the relations obtained to give some results about $(M,g_L)$.