Tensionless string spectra on AdS3

Abstract

The spectrum of superstrings on AdS3 × S3 × M4 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 M4 = S3 × S1 and M4 = T4 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 AdS3 × S3 × T4 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.