# IAS Physics Group Meeting

## On Type II String Theory on $AdS_3$ x $S^3$ x $T^4$ and Symmetric Orbifolds

**Abstract:** I will present some questions and answers regarding the duality between 1+1-dimensional superconformal field theory and type II string theory on $AdS_3 \times S^3 x T^4$.

For one unit of NS-NS 5-brane flux ($Q_5$=1), this string theory has been suggested to be dual to a grand-canonical ensemble of $T^{4N}/S_N$ free symmetric orbifold CFTs. We explain how the string genus expansion emerges to all orders for the free orbifold grand-canonical correlation functions.

We also discuss how the strong coupling limit of the NS-NS string theory arises (even at large $N$) in the free orbifold description, and argue why this limit does not have a weakly coupled R-R description.

The dual CFT includes (for all values of $Q_5$) an extra $T^4$ factor which decouples from perturbative string theory. We discuss the exactly-marginal deformations that relate the different values of $Q_5$, including the precise $J{\bar J}$ deformations mixing this extra $T^4$ with the symmetric orbifold.