Lifting 1/4-BPS states in AdS3× S3 × T4

A bstract We establish a framework for doing second order conformal perturbation theory for the symmetric orbifold Sym N ( T 4 ) to all orders in N . This allows us to compute how 1/4-BPS states of the D1-D5 system on AdS 3 × S 3 × T 4 are lifted as we move away from the orbifold point. As an application we confirm a previous observation that in the large N limit not all 1/4-BPS states that can be lifted do get lifted. This provides evidence that the supersymmetric index actually undercounts the number of 1/4-BPS states at a generic point in the moduli space.