Gauge fields and particle-like formations associated with shear-free   null congruences
  We consider Maxwell fields associated with any shear-free null geodesic congruence on Minkowski or Riemannian background space-time. Bounded singular loci of these fields are treated as particle-like formations, possess "self-quantized" electric charge and undergo self-consistent time dynamics. Complicated singular solutions of Maxwell (as well as related complex Yang-Mills) equations can be obtained in a purely algebraic way using the Kerr theorem. 
Vladimir V. Kassandrov, Vladimir N. Trishin