SL(2,Z) symmetries, Supermembranes and Symplectic Torus Bundles
  We give the explicit formulation of the 11D supermembrane as a symplectic torus bundle with non trivial monodromy and non vanishing Euler class. This construction allows a classification of all supermembranes showing explicitly the discrete SL(2,Z) symmetries associated to dualities. It hints as the origin in M-theory of the gauging of the effective theories associated to string theories. 
M. P. Garc\'ia del Moral, I. Mart\'in, J. M. Pe\~na and A. Restuccia
hep-th math-ph math.MP