Virasoro constraint for Nekrasov instanton partition function
  We show that Nekrasov instanton partition function for SU(N) gauge theories satisfies recursion relations in the form of U(1)+Virasoro constraints when {\beta} = 1. The constraints give a direct support for AGT conjecture for general quiver gauge theories. 
Shoichi Kanno, Yutaka Matsuo and Hong Zhang
hep-th math-ph math.MP