Conformal blocks of chiral fields in N = 2 SUSY CFT and affine Laumon spaces

We consider the problem of computing N = 2 superconformal block functions. We argue that the Kazama-Suzuki coset realization of N = 2 superconformal algebra in terms of the affine sl̂(2) algebra provides relations between N = 2 and sl̂(2) conformal blocks. We show that for N = 2 chiral fields the corresponding sl̂(2) construction of the conformal blocks is based on the ordinary highest weight representation. We use an AGT-type correspondence to relate the four-point sl̂(2) conformal block with Nekrasov's instanton partition functions of a four-dimensional N = 2 SU(2) gauge theory in the presence of a surface operator. Since the previous relation proposed by Alday and Tachikawa requires some special modification of the conformal block function, we revisit this problem and find direct correspondence for the four-point conformal block. We thus find an explicit representation for the sl̂(2) four-point conformal block and hence obtain an explicit combinatorial representation for the N = 2 chiral four-point conformal block.