Pseudo-duality

Proper symmetries act on fields while pseudo-symmetries act on both fields and coupling constants. We identify the pseudo-duality groups that act as symmetries of the equations of motion of general systems of scalar and vector fields and apply our results to N = 2,4 and 8 supergravity theories. We present evidence that the pseudo-duality group for both the heterotic and type II strings totoidally compactified to four dimensions is Sp(56;Z) × D, where D is a certain subgroup of the diffeomorphism group of the scalar field target space. This contains the conjectured heterotic S × T or type II U proper duality group as a subgroup.