Affine <Emphasis Type="Italic">SL</Emphasis>(2) Conformal Blocks from 4d Gauge Theories

We study Nekrasov’s instanton partition function of four-dimensional N=2{\mathcal{N}=2} gauge theories in the presence of surface operators. This can be computed order by order in the instanton expansion by using results available in the mathematical literature. Focusing in the case of SU(2) quiver gauge theories, we find that the results agree with a modified version of the conformal blocks of affine SL(2) algebra. These conformal blocks provide, in the critical limit, the eigenfunctions of the corresponding quantized Hitchin Hamiltonians.