Tensionless string spectra on AdS3

A bstract The spectrum of superstrings on AdS 3 × S 3 × M M 4 with pure NS-NS flux is analysed for the background where the radius of the AdS space takes the minimal value ( k = 1). Both for M M 4 = S 3 × S 1 and M M 4 = T T 4 we show that there is a special set of physical states, coming from the bottom of the spectrally flowed continuous representations, which agree in precise detail with the single particle spectrum of a free symmetric product orbifold. For the case of AdS 3 × S 3 × T T 4 this relies on making sense of the world-sheet theory at k = 1, for which we make a concrete proposal. We also comment on the implications of this striking result.