Normal ordering and boundary conditions for fermionic string coordinates
  We build up normal ordered products for fermionic open string coordinates consistent with boundary conditions. The results are obtained considering the presence of antisymmetric tensor fields. We find a discontinuity of the normal ordered products at string endpoints even in the absence of the background. We discuss how the energy momentum tensor also changes at the world-sheet boundary in such a way that the central charge keeps the standard value at string end points. 
Nelson R. F. Braga, Hector L. Carrion and Cresus F. L. Godinho