Recently it has been speculated that the S-matrix elements on the world volume of D3-branes should satisfy the Ward identity corresponding to the S-duality transformations. For a single brane and in the low energy limit, this indicates that in the Abelian Dirac-Born-Infeld and Chern-Simons actions, the combination of contact terms and tree-level massless poles in an n-point function should satisfy the S-duality. In this paper, we examine in details the S-matrix element of three gauge bosons and one 2-form and the S-matrix element of six gauge bosons in favor of the above proposal.

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