Low-energy effective action in 5D,N=2 supersymmetric gauge theory

We construct N=2 supersymmetric low-energy effective action of 5D,N=2 supersymmetric Yang–Mills (SYM) theory in 5D,N=1 harmonic superspace. It is obtained as a hypermultiplet completion of the leading Wln⁡W-term in the N=1 SYM low-energy effective action by invoking the second implicit on-shell N=1 supersymmetry. After passing to components, the N=2 effective action constructed displays, along with other terms, the SO(5)-invariant F4/X3 term. Though we specialize to the case of SU(2) gauge group spontaneously broken to U(1), our consideration is applicable to any gauge symmetry broken to some abelian subgroup.