Integrability and Conformal Symmetry in Higher Dimensions: A Model with   Exact Hopfion Solutions
  We use ideas on integrability in higher dimensions to define Lorentz invariant field theories with an infinite number of local conserved currents. The models considered have a two dimensional target space. Requiring the existence of Lagrangean and the stability of static solutions singles out a class of models which have an additional conformal symmetry. That is used to explain the existence of an ansatz leading to solutions with non trivial Hopf charges. 
O. Babelon and L. A. Ferreira