Superstrings on NS5 backgrounds, deformed AdS3 and holography
Résumé
We study a non-standard decoupling limit of the D1/D5-branesystem, which interpolates between the near-horizon geometry ofthe D1/D5 background and the near-horizon limit of the pureD5-brane geometry. The S-dual description of this background isactually an exactly solvable two-dimensional (worldsheet)conformal field theory: {null-deformed SL(2,R)} xSU(2) x T^4 or K3. This model is free of strong-couplingsingularities. By a careful treatment of the SL(2,R),based on the better-understood SL(2,R) / U(1) coset, weobtain the full partition function for superstrings onSL(2,R) x SU(2) x K3. Thisallows us to compute the partition functions for the J^3and J^2 current-current deformations, as well as the fullline of supersymmetric null deformations, which links theSL(2,R) conformal field theory with linear dilatontheory. The holographic interpretation of this setup is arenormalisation-group flow between the decoupled NS5-braneworld-volume theory in the ultraviolet (Little String Theory), andthe low-energy dynamics of super Yang--Mills string-likeinstantons in six dimensions.