A defect in AdS3/CFT2 duality

AdS3 string theory in the stringy regime k = (RAdS/ℓs)2< 1 provides a laboratory for the study of holography in which both sides of AdS/CFT duality are under fairly good control. Worldsheet string theory is solvable, and for closed strings the dual spacetime CFT is a deformation of a symmetric product orbifold. Here we extend this construction to include open strings by adding a probe D-string, described semiclassically by an AdS2 D-brane in AdS3. The dual defect or boundary conformal field theory (BCFT) is again a deformed symmetric product, which now describes the Fock space of long open and closed strings near the AdS boundary, with a boundary deformation implementing the open/closed transition in addition to the symmetric product ℤ2 twist deformation that implements closed string joining/splitting. The construction thus provides an explicit example of an AdS3/BCFT2 duality.