Space-time supersymmetry, IIA/B duality and M-theory

The connection between IIA superstring theory compactified on a circle of radius R and IIB theory compactified on a circle of radius 1/R is reexamined from the perspective of N = 2, D = 9 space-time supersymmetry. We argue that the consistency of IIA/B duality requires the BPS states corresponding to momentum and winding of either of the type-II superstrings to transform as inequivalent supermultiplets. We show that this is indeed the case far any finite compactification radius, thus providing a nontrivial confirmation of IIA/B duality. From the point of view of N = 2, D = 9 supergravity, one is naturally led to an SL(2,Z) invariant field theory that encompasses both the M-theory torus and the Kaluza-Klein states of the IIB theory. (C) 1999 Published by Elsevier Science B.V. All rights reserved.