On higher derivative terms in tachyon effective actions

Abstract

We reconstruct the tachyon effective action for unstable D-branes in\nsuperstring theory by examining its behaviour near exactly marginal\ndeformations, where the ambigous higher derivative terms can be eliminated. We\nthen compare this action with that obtained in boundary string field theory and\nfind remarkable agreement. In particular, the tension for lower dimensional\nbranes and the BI-action for the centre of mass motion are reprodued exactly.\nWe also comment on the action for tachyons on the kink in a\nD-brane/anti-D-brane system and on bosonic string theory.\n