The problem with the U-duality transformation of membrane on Tn is
recently addressed in [arXiv:1509.02915 [hep-th]]. We will consider the
U-duality transformation rule of membrane on Tn×R. It turns out that
winding modes on Tn 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)×SL(3,Z) and SL(5,Z) symmetries for n=3 and n=4, respectively. The
SL(2,Z)×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).Comment: 19 pages; v2: 20 pages, reference corrected, extended discussion in
section 5, journal versio