Non-Abelian expansion of S-matrix elements and non-Abelian tachyon DBI action Original Research Article

We apply the prescription proposed in hep-th/0307197 for non-Abelian expansion of S-matrix elements, to the S-matrix element of four tachyons and one gauge field in superstring theory. We show that the leading order terms of the expansion are in perfect agreement with the non-Abelian generalization of the tachyon DBI action in which the tachyon potential is image where image is the mass of tachyon. This calculation fixes the coefficient of four-tachyon couplings without on-shell ambiguity.