Fiber-base duality and global symmetry enhancement

We show that the 5D Nekrasov partition functions enjoy the enhanced global symmetry of the UV fixed point. The fiber-base duality is responsible for the global symmetry enhancement. For SU(2) with N f ≤ 7 flavors the fiber-base symmetry together with the manifest flavor SO(2N f ) symmetry generate the E_Nf+1 global symmetry, while in the higher rank case the manifest global symmetry of the two dual theories related by the fiber-base duality map generate the symmetry enhancement. The symmetry enhancement at the level of the partition function is manifest once we chose an appropriate reparametrization for the Coulomb moduli.