Superstrings on AdS3 at k=1
G. Giribet, C. Hull, M. Kleban, M. Porrati, E. Rabinovici
TL;DR
The paper analyzes superstrings on AdS$_3$ with NS-NS flux at the special k=1 regime, identifying a phase where long strings dominate and a continuum of massless higher-spin states emerges. It proposes a concrete holographic dual: a symmetric-product SCFT on $(R imes c{N})^N/S_N$ with a carefully chosen seed, and demonstrates that, in the large-N limit, this dual reproduces the full long-string spectrum (including non-BPS states) of the bulk theory. The work provides strong evidence for a concrete, exactly-matchable holographic description at a string-scale curvature, offering insights into tensionless-like phases and stringy symmetries in AdS$_3$. It also discusses subtleties in comparing bulk amplitudes to boundary correlators and outlines avenues for refining the dual and understanding interactions. Overall, it reveals that a simple symmetric-orbifold CFT captures the intricate long-string physics at the AdS$_3$ transition point, with potential implications for broader holographic dualities at highly curved or tensionless limits.
Abstract
We study superstring theory in three dimensional Anti-de Sitter spacetime with NS-NS flux, focusing on the case where the radius of curvature is equal to the string length. This corresponds to the critical level k=1 in the Wess-Zumino-Witten description. Previously, it was argued that a transition takes place at this special radius, from a phase dominated by black holes at larger radius to one dominated by long strings at smaller radius. We argue that the infinite tower of modes that become massless at k=1 is a signal of this transition. We propose a simple two-dimensional conformal field theory as the holographic dual to superstring theory at k=1. As evidence for our conjecture, we demonstrate that at large N our putative dual exactly reproduces the full spectrum of the long strings of the weakly coupled string theory, including states unprotected by supersymmetry.
