Boundary Fluctuations of AdS String

We analyse the world-sheet perturbations of string theory formulated around $AdS_3$ background. We identify a set of operators that, while added to the world-sheet action, generate the boundary fluctuations of $AdS_3$. The effect of these operators can be collectively defined in terms of Liouville field living on the $AdS_3$ boundary. We then study various deformations of $AdS_3$ generated by boundary fluctuations by turning on suitable world-sheet couplings. We also discuss certain small fluctuations around the BTZ black hole.