Critical fields on the M5-brane and noncommutative open strings

The M5-brane is investigated near critical held-strength. We show that this limit on the M5-brane reduces to the noncommutative open string limit on t he D4-brane. The reduction on a two-toms leads to both the noncommutative o pen string limit and the noncommutative Yang-Mills limit on the D3-brane. T he decoupled noncommutative five-brane is identified with the strong coupli ng limit of the noncommutative open string theory on the D4-brane and S-dua lity on the noncommutative D3-brane is identified with a modular transforma tion on the five brane. We argue that the open membrane metric defines a fi nite length scale on the worldvolume of the M5-brane in the decoupling limi t. This length scale can be associated to the effective length scale of an open membrane. (C) 2000 Elsevier Science B.V. All rights reserved.