Yang-Mills Instantons from Gravitational Instantons
  We show that every gravitational instantons are SU(2) Yang-Mills instantons on a Ricci-flat four manifold although the reverse is not necessarily true. It is shown that gravitational instantons satisfy exactly the same self-duality equation of SU(2) Yang-Mills instantons on the Ricci-flat manifold determined by the gravitational instantons themselves. We explicitly check the correspondence with several examples and discuss their topological properties. 
John J. Oh, Chanyong Park and Hyun Seok Yang
hep-th gr-qc