The all-loop integrable spin-chain for strings on AdS3 x S3 x T4: the massive sector

We bootstrap the all-loop dynamic S-matrix for the homogeneous psu(1, 1 vertical bar 2)(2) spin-chain believed to correspond to the discretization of the massive modes of string theory on AdS(3) x S-3 x T-4. The S-matrix is the tensor product of two copies of the su(1 vertical bar 1)(2) invariant S-matrix constructed recently for the partial derivative(2, 1; alpha)(2) chain, and depends on two anti-symmetric dressing phases. We write down the crossing equations that these phases have to satisfy. Furthermore, we present the corresponding Bethe Ansatz, which differs from the one previously conjectured, and discuss how our construction matches several recent perturbative calculations.