On string theory on AdS3 x S3 x T4 with mixed 3-form flux: Tree-level S-matrix

We consider superstring theory on AdS(3) x S-3 x T-4 supported by a combination of RR and NSNS 3-form fluxes (with parameter of the NSNS 3-form q). This theory interpolates between the pure RR flux model (q = 0) whose spectrum is expected to be described by a (thermodynamic) Bethe ansatz and the pure NSNS flux model (q = 1) which is described by the supersymmetric extension of the SL(2, R) x SU(2) WZW model. As a first step towards the solution of this integrable theory for generic value of q we compute the corresponding tree-level S-matrix for massive BMN-type excitations. We find that this S-matrix has a surprisingly simple dependence on q: the diagonal amplitudes have exactly the same structure as in the q = 0 case but with the BMN dispersion relation e(2) = p(2) + 1 replaced by the one with shifted momentum and mass, e(2) = (p +/- q)(2) + 1 - q(2). The off-diagonal amplitudes are then determined from the classical Yang Baxter equation. We also construct the Pohlmeyer-reduced model corresponding to this superstring theory and find that it depends on q only through the resealed mass parameter, mu -> root 1 - q(2)mu, implying that its relativistic S-matrix is q-independent. (C) 2013 Elsevier B.V. All rights reserved.