Path Integral Equivalence between Super D-string and IIB Superstring
  We show that the super D-string action is exactly equivalent to the IIB Green-Schwarz superstring action with some "theta term" in terms of the path integral. Since the "theta term" imposes the Gauss law constraint on the physical state but contributes to neither the mass operator nor the constraints associated with the kappa symmetry and the reparametrization, this exact equivalence implies that the impossibility to disentangle the first and second class fermionic constraints covariantly in the super D-string action is generally inherited from the IIB Green-Schwarz superstring action except specific gauge choices which make the ground state massive, such as the static gauge. Moreover, it is shown that if the electric field is quantized to be integers, the super D-string action can be transformed to the IIB Green-Schwarz superstring action with $SL(2, Z)$ covariant tension. 
Ichiro Oda (Edogawa Univ.)