On effective actions of non-BPS branes and their higher derivative corrections

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 higher derivative corrections. In particular, we have found that there is exact consistency between field theory and string theory tachyon pole of S-matrix element of one RR and three tachyons provided that one takes into account the fact that the tachyon vertex operator in 0 picture to be along the Pauli matrix σ1σ1 whereas the tachyon in −1 picture to be along the σ2σ2 direction. This internal CP factors should be included in the tachyon DBI part of the effective action.