Boundary states and non-abelian orbifolds
  In this note the open string partition function is analyzed carefully in a way to reveal the group-theoretical aspects. For the simple cases of ADE orbifolds with regular Chan-Paton action a prescription for consistent boundary states is given. In the process of outlining how they encode McKay correspondence, we argue that this results from a non-trivial conspiracy of numerical factors in the string amplitudes. 
Frederik Roose