Tachyon couplings on non-BPS D-branes and Dirac-Born-Infeld action

TL;DR

Garousi analyzes tachyon couplings on non-BPS D-branes by computing disk S-matrix elements in a constant $B$-field background and derives an extended tachyon-DBI action that nonlinearly includes the tachyon via a potential $V(T)$ and a kinetic term under the determinant. He builds a Seiberg-Witten-type map to noncommutative open-string fields, enabling direct comparison with noncommutative amplitudes, and verifies the action by matching massless poles and contact terms in both open- and closed-string channels. The work further extends the abelian construction to a non-Abelian setting for $N$ coincident branes using a symmetric-trace prescription and T-duality from a D9-brane action. Together, these results provide a coherent tachyon-augmented DBI framework that connects world-sheet amplitudes to effective world-volume dynamics and informs tachyon condensation in non-BPS systems.

Abstract

By explicit evaluation of certain disk S-matrix elements in the presence of background B-flux, we find coupling of two open string tachyons to gauge field, graviton, dilaton or Kalb-Ramond antisymmetric tensor on the world-volume of a single non-BPS D$p$-brane. We then propose an extension of the abelian Dirac-Born-Infeld action which naturally reproduces these couplings in field theory. This action includes non-linearly the dynamics of the tachyon field much like the other bosonic modes of the non-BPS D$p$-brane. On the general grounds of gauge and T-duality transformations and the symmetrized trace prescription, we then extend the abelian action to non-abelian cases.