The Interaction of Dirac Particles with Non-Abelian Gauge Fields and   Gravity - Bound States
  We consider a spherically symmetric, static system of a Dirac particle interacting with classical gravity and an SU(2) Yang-Mills field. The corresponding Einstein-Dirac-Yang/Mills equations are derived. Using numerical methods, we find different types of soliton-like solutions of these equations and discuss their properties. Some of these solutions are stable even for arbitrarily weak gravitational coupling. 
Felix Finster, Joel Smoller, and Shing-Tung Yau