Three-point functions for MN/SN orbifolds with N=4 supersymmetry

The D1-D5 system is believed to have an orbifold point in its moduli space where its low energy theory is a N = 4 supersymmetric sigma model with target space M-N/S-N, where M is T-4 or K3. We study correlation functions of chiral operators in CFTs arising from such a theory. We construct a basic class of chiral operators from twist fields of the symmetric group and the generators of the superconformal algebra. We find explicitly the 3-point functions for these chiral fields at large N; these expressions are universal in that they are independent of the choice of M. We observe that the result is a significantly simpler expression than the corresponding expression for the bosonic theory based on the same orbifold target space.