U-duality transformation of membrane on Tn revisited

The problem with the U-duality transformation of membrane on T-n is recently addressed in [arXiv:1509.02915]. We will consider the U-duality transformation rule of membrane on T-n x R. It turns out that winding modes on T-n should be taken into account, since the duality transformation may bring the membrane configuration without winding modes into the one with winding modes. With the winding modes added, the membrane worldvolume theory in lightcone gauge is equivalent to the n + 1 dimensional super-Yang-Mills (SYM) theory in T-n which has SL(2, Z) x SL(3, Z) and SL(5, Z) symmetries for n = 3 and n = 4, respectively. The SL(2, Z) x SL(3, Z) transformation can be realized classically, making the on-shell field configurations transformed into each other. However, the SL(5, Z) symmetry may only be realized at the quantum level, since the classical 5d SYM field configurations cannot form the representation of SL(5, Z).