Tensionless Limit of Pure-Ramond-Ramond Strings and AdS_{3}/CFT_{2}.

Despite impressive advances in the AdS_{3}/CFT_{2} correspondence, the setup involving Ramond-Ramond backgrounds, which is related to the D1-D5 system of branes, remained relatively poorly understood. We use the mirror thermodynamic Bethe ansatz (TBA) equations recently constructed by Frolov and Sfondrini to study the spectrum of pure Ramond-Ramond AdS_{3}×S^{3}×T^{4} strings. We find that the leading-order contribution to the anomalous dimensions at small tension is due to the gapless world-sheet excitations, i.e., to the T^{4} bosons and their superpartners, whose interactions are nontrivial.

Root-TT[over ¯] Deformations in Two-Dimensional Quantum Field Theories.

In this Letter, we introduce a one-parameter deformation of two-dimensional quantum field theories generated by a nonanalytic operator that we call Root-TT[over ¯]. For a conformal field theory, the operator coincides with the square root of the TT[over ¯] operator. More generally, the operator is defined so that classically it is marginal and generates a flow that commutes with the TT[over ¯] flow. Intriguingly, the Root-TT[over ¯] flow is closely related to the ModMax theory recently constructed by Bandos, Lechner, Sorokin, and Townsend.

Flow Equations for Generalized TT[over ¯] Deformations.

We consider the most general set of integrable deformations extending the TT[over ¯] deformation of two-dimensional relativistic QFTs. They are CDD deformations of the theory's factorized S matrix related to the higher-spin conserved charges. Using a mirror version of the generalized Gibbs ensemble, we write down the finite-volume expectation value of the higher-spin charges, and derive a generalized flow equation that every charge must obey under a generalized TT[over ¯] deformation. This also reproduces the known flow equations on the nose.

TT[over ¯] Deformations and Integrable Spin Chains.

We consider current-current deformations that generalize TT[over ¯] ones, and show that they may be also introduced for integrable spin chains. In analogy with the integrable QFT setup, we define the deformation as a modification of the S matrix in the Bethe equations. Using results by Bargheer, Beisert and Loebbert we show that the deforming operator is composite and constructed out of two currents on the lattice; its expectation value factorizes like for TT[over ¯]. Such a deformation may be considered for any combination of charges that preserve the model's integrable structure.

Towards the all-loop worldsheet S matrix for AdS3×S³×T4.

We obtain the all-loop worldsheet S matrix for fundamental excitations on AdS3×S³×T4 by studying the off-shell symmetry algebra of the superspace action in light cone gauge. The massless modes, unaccounted for in earlier works, are automatically included in our treatment. Their exact dispersion relation is found to be nonrelativistic, of giant-magnon form, and their scattering is naturally well defined. This opens the way to a complete investigation of AdS3/CFT2 integrability.