On NS-NS couplings at order α′3

Recently, imposing the gauge-symmetry and the T-duality constraints on the string frame effective actions of type II superstring theories at order alpha'(3), the NS-NS couplings have been found in a particular scheme which has 445 couplings in 15 different structures. In this paper, using a field redefinition, we write them in terms of 251 couplings which appear in 9 different structures. The 9 structures involve only Riemann curvature, H-alpha beta mu and del H-alpha(beta mu nu). The number of couplings in the structures R-4, H-8, (HR)-R-6, (HR2)-R-4, (HR3)-R-2 are 2, 2, 1, 7, 22, respectively, and the number of couplings in the structures (del H)(4), (del H)R-2(2), (del H)H-2(4), (del H)(HR)-H-2-R-2 are 12, 22, 77, 106, respectively. The new couplings are also fully consistent with the sphere-level S-matrix element of four NS-NS vertex operators. (C) 2021 The Author. Published by Elsevier B.V.