On T-duality for open strings in general abelian and nonabelian gauge   field backgrounds
  We discuss T-duality for open strings in general background fields both in the functional integral formulation as well as in the language of canonical transformations. The Dirichlet boundary condition in the dual theory has to be treated as a constraint on the functional integration. Furthermore, we give meaning to the notion of matrix valued string end point position in the presence of nonabelian gauge field background. 
H. Dorn, H.-J. Otto (Humboldt university Berlin)