Critical fields on the M 5 – brane and noncommutative open strings

The M5–brane is investigated near critical field-strength. We show that this limit on the M5–brane reduces to the noncommutative open string limit on the D4–brane. The reduction on a two–torus leads to both the noncommutative open string limit and the noncommutative Yang–Mills limit on the D3–brane. The decoupled noncommutative five–brane is identified with the strong coupling limit of the noncommutative open string theory on the D4– brane and S–duality on the noncommutative D3–brane is identified with a modular transformation on the five–brane. We argue that the open membrane metric defines a finite length scale on the worldvolume of the M5–brane in the decoupling limit. This length scale can be associated to the effective length scale of an open membrane. [email protected] [email protected] [email protected] [email protected]