T-duality and Actions for Non-BPS D-branes

TL;DR

The paper addresses how T-duality restricts the tachyon dependence in effective actions for non-BPS D-branes in Type II string theories. It argues that the Born-Infeld term can be consistently extended to include the tachyon through a determinant involving $\partial_i T$, i.e. $S_{ m BI}^{(p)} = -\int d^{p+1}\sigma \, \sqrt{\det(G_{ij} + \partial_i T \partial_j T)}\, g(T)$, and shows that this form is compatible with both T-duality and supersymmetry. The Wess-Zumino terms are analyzed similarly, with coefficients fixed by T-duality to produce consistent RR couplings upon reduction to nine dimensions; together these results reinforce a coherent picture of non-BPS branes and their descent to BPS branes via tachyon condensation. The findings illuminate tachyon dynamics within a duality-consistent framework and suggest avenues for embedding non-BPS branes into M-theory, potentially via kink condensation to D(p-1)-branes. Overall, the work provides a structured method to constrain tachyon couplings and enriches our understanding of brane descent relations and duality symmetries in string theory.

Abstract

We employ T-duality to restrict the tachyon dependence of effective actions for non-BPS D-branes. For the Born-Infeld part the criteria of T-duality and supersymmetry are satisfied by a simple extension of the D-brane Born-Infeld action.