“…In the large B-field background, the noncommutative structure can be approximated by the Poisson bracket. In fact, the low energy effective theory of M5-brane in large C-field background has already been shown [6,8] to agree with both D4-brane in NS-NS B-field background and D4-brane in RR C-field background, depending on whether the direction of compactification is xμ =5 or x 2 . Since the D4-brane theories for the two different backgrounds reduce to D3-branes in NS-NS B-field or RR field background through dimensional reduction on x 2 or xμ =5 , respectively, it is more or less obvious that, to the leading order (Poisson approximation), the noncommutative U(1) gauge theory is dual (equivalent) to the effective theory defined by (48) for p = 3, as they are both dimensional reduction of the same M5-brane theory on a torus in the directions of x 2 and xμ =5 .…”