Hitchin's equations and integrability of BPS Z(N) strings in Yang-Mills   theories
  We show that Z(N) string's BPS equations are equivalent to the Hitchin's equations (or self-duality equation) and also to the zero curvature condition. We construct a general form for BPS Z(N) string solutions for arbitrary simple gauge groups with non-trivial center. Depending on the vacuum solutions considered, the Z(N) string's BPS equations reduce to different two dimensional integrable field equations. For a particular vacuum we obtain the equation of affine Toda field theory. 
Marco A. C. Kneipp