S-matrix elements and covariant tachyon action in type 0 theory Original Research Article

We evaluate the sphere level S-matrix element of two tachyons and two massless NS states, the S-matrix element of four tachyons, and the S-matrix element of two tachyons and two Ramond–Ramond vertex operators, in type 0 theory. We then find an expansion for theses amplitudes that their leading order terms correspond to a covariant tachyon action. To the order considered, there are no image, image, image, nor image tachyon couplings, whereas, the tachyon couplings image and image are non-zero.