The complete worldsheet S matrix of superstrings on AdS3×S3×T4AdS3×S3×T4 with mixed three-form flux

We determine the off-shell symmetry algebra and representations of Type IIB superstring theory on AdS3×S3×T4AdS3×S3×T4 with mixed R–R and NS–NS three-form flux. We use these to derive the non-perturbative worldsheet S matrix of fundamental excitations of the superstring theory. Our analysis includes both massive and massless modes and shows how turning on mixed three-form flux results in an integrable deformation of the S matrix of the pure R–R theory.