Tachyon Couplings to Fermion

TL;DR

This paper investigates tachyon-fermion interactions on non-BPS D-branes, calculating specific S-matrix elements, and confirms the consistency of these couplings with the supersymmetric tachyon DBI action at low energy.

Contribution

It determines the internal CP factors of disk-level S-matrix elements involving fermions and tachyons, and compares the derived couplings with the supersymmetric tachyon DBI action.

Findings

Internal CP factor of certain amplitudes is zero.

Calculated the two-fermion-two-tachyon amplitude and its momentum expansion.

Found exact agreement between string theory couplings and the tachyon DBI action.

Abstract

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 vertex operators in the world volume of non-BPS D-branes/D-brane-anti-D-brane is zero. We have calculated the S-matrix element of two fermions and two tachyons which has non vanishing internal CP factor, and found the momentum expansion of this amplitude. In the abelian case, we have compared the two-fermion-two-tachyon coupling at low energy with the corresponding coupling in the gauge-fixed supersymmetric tachyon DBI action. The couplings in the two cases are exactly the same.