Stringy AdS3 from the Worldsheet

TL;DR

This work analyzes tensionless limits of bosonic strings on $AdS_3$ with H-flux by examining the worldsheet $SL(2,\mathbb{R})_k$ WZW spectrum, including spectrally flowed sectors, under the physical-state mass-shell constraints. It identifies a novel tensionless regime at $k=3$, where an infinite stringy tower of massless higher-spin fields emerges as part of a continuum arising from long-string-like modes near the boundary. The continuum nature and the emergence of massless higher spins are tied to the interplay between H-flux and string tension, and differ from the symmetric-orbifold tensionless limit seen in AdS$_3$ superstring setups. The results hint at new forms of higher-spin symmetry and potential noncompact directions in the dual CFT, with Liouville-like long-string dynamics providing a useful interpretive framework.

Abstract

We investigate the behaviour of the bosonic string on AdS3 with H-flux at stringy scales, looking in particular for a `tensionless' limit in which there are massless higher spin gauge fields. We do this by revisiting the physical spectrum of the sl(2,R)$_k$ WZW model and considering the limit in which k becomes small. At k=3 we find that there is an infinite stringy tower of massless higher spin fields which are part of a continuum of light states. This can be viewed as a novel tensionless limit, which appears to be distinct from that inferred from the symmetric orbifold description of superstring AdS3 vacua.