By explicit calculation, we show that the expansion of the disk level S-matrix element of one RR field, two open string tachyons and one gauge field that has been recently found corresponds to the derivative expansion of ...

We examine the proposal for constructing the effective action of a D-brane-anti-D-brane system from the non-abelian extension of tachyon DBI action. We consider two prescriptions for the trace in the non-abelian tachyon ...

By calculating various disk level S-matrix elements and studying in details their momentum expansions, we have extracted some of the couplings in tachyon DBI action and Wess-Zumino terms of the non-BPS branes, and their ...

We use compatibility of O-plane action with nonlinear T-duality as a guiding principle to find all NS-NS couplings in the O-plane action at order $\\alpha'^2$. We find that the dilaton couplings appear in the string ...

A nonlinear SO(8) invariant BF type Lagrangian for describing the dynamics of N M2-branes in flat spacetime has been proposed recently in the literature which is an extension of the non-abelian DBI action of N D2-branes. ...

By fixing the internal CP factor of tachyon and massless Ramond vertex operators in different pictures, we have shown that the internal CP factor of the disk level S-matrix elements of two fermions and odd number of tachyon ...

By explicit calculations of four-field couplings, we observe that the higher derivative corrections to the DBI action in flat space-time, can be either in a covariant form or in a T-duality invariant form. The two forms ...

We use compatibility of the second fundamental form corrections to Dirac-Born-Infeld action at order

α′2 which includes the trace of the second fundamental form, with T-duality and with the linear S-duality ...

There is a conjecture in the literature that indicates the tree-level S-matrix elements of graviton become symmetric under the SL(2,Z) transformation after including the loops and the nonperturbative effects. Using the ...

We evaluate various disk level four-point functions involving the massless scalar and tachyon vertex operators in the presence of background B-flux in superstring theory. By studying these amplitudes in specific limits, ...