The effectiveness of relativistic invariance in AdS 3

bstract We use relativistic invariance to investigate two aspects of integrable AdS 3 string theory. Firstly, we write down the all-loop TBA equations for the massless sector of the theory with R-R flux, using the recently discovered hidden relativistic symmetry. Secondly, for the low-energy relativistic limit of the theory with NS-NS flux we write down the S matrix, dressing factors and TBA. We find that the integrable system coincides with a restriction to AdS 3 of the relativistic q-deformed AdS 5 theory. We also comment on the relativistic limit of the small- k NS-NS theory.