Ramond-Ramond Couplings on Brane-Antibrane Systems

TL;DR

Kennedy and Wilkins compute couplings between Ramond-Ramond fields and open strings in systems of coincident branes and antibranes in type II theory. Using disc-level string amplitudes, they show an additional tachyon-dependent contact interaction and recast the result in terms of a superconnection curvature ${\cal F}$, yielding the compact action $S = \int C \wedge \mathrm{STr}\, e^{\cal F}$. The two-point RR–tachyon amplitude vanishes, while the three-point RR–tachyon–tachyon amplitude produces a low-energy coupling $H_{(p)} \wedge \mathrm{Tr}(\bar{T} DT)$, consistent with integration by parts and covariantization. These findings provide a unified RR coupling framework for brane-antibrane systems via noncommutative geometry notions and the transgression formula, and they reproduce the correct charges of decay products after tachyon condensation. The work links tachyon dynamics to D-brane charge via a curvature-based Wess-Zumino-type action, with potential implications for the K-theory classification of brane charges.

Abstract

Couplings between a closed string RR field and open strings are calculated in a system of coincident branes and antibranes of type II theory. The result can be written cleanly using the curvature of the superconnection.