Gauge Invariant Matrix Model for the \^A-\^D-\^E Closed Strings
  The models of triangulated random surfaces embedded in (extended) Dynkin diagrams are formulated as a gauge-invariant matrix model of Weingarten type. The double scaling limit of this model is described by a collective field theory with nonpolynomial interaction.   The propagator in this field theory is essentially two-loop correlator in the corresponding string theory. 
I. Kostov