Dualities as symmetries of the Supermembrane Theory
  In this note I review the role played by dualities in the Supermembrane Theory compactified on a torus. Supermembrane theory realize S, T, so U-duality, as exact symmetries of the theory. There are two well defined sectors: with and without central charges. Both sectors have the SL(2,Z)xZ2 U-duality group in 9D as a symmetry of the theory, but the supermembrane with central charges, also exhibits an extra SL(2,Z) symmetry of the theory associated to the diffeomorphisms not connected with the identity changing the homology basis. The Z2 symmetry is T-duality transformation that acts on the supermembrane and generalize that of the string. This T-duality transformation acts locally and also globally on the supermembrane theory. It has a natural description in terms of the cohomology of the base manifold and the homology of the target torus. When only string-like states are preserved, one recovers both type II string theories in 9D. If one also consider properly limit of the T-duality transformation characterizing the supermembrane, the usual closed string T-duality transformation between the type IIA and type IIB mass operators is recovered. 
M.P. Garcia del Moral
hep-th