Noncommutative gauge dynamics from brane configurations with background B field

We study D=3 field theories on D3-branes stretched between two NS5-branes with NS B field background. The theory is a noncommutative gauge theory. The mirror symmetry and S-duality of the theory are discussed. A new feature is that the mirror of the noncommutative gauge theory is not a field theory but an open string decoupled from the closed string. We also consider brane creation phenomena and use the result to discuss the analogue of the Seiberg duality. A noncommutative soliton is interpreted as a D1-brane induced on a D3-brane. (author)