Yang-Mills Instantons in the Gravitational Instanton Backgrounds
  The simplest and the most straightforward new algorithm for generating solutions to (anti) self-dual Yang-Mills (YM) equation in the typical gravitational instanton backgrounds is proposed. When applied to the Taub-NUT and the Eguchi-Hanson metrics, the two best-known gravitational instantons, the solutions turn out to be the rather exotic type of instanton configurations carrying finite YM action but generally fractional topological charge values. 
Hongsu Kim and Yongsung Yoon (Hanyang Univ., Korea)