LAUSR

Abstract We construct N = 2 supersymmetric low-energy effective action of 5 D , N = 2 supersymmetric Yang–Mills (SYM) theory in 5 D , N = 1 harmonic superspace. It is obtained as a hypermultiplet completion of the leading W ln ⁡ 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 S O ( 5 ) -invariant F 4 / X 3 term. Though we specialize to the case of S U ( 2 ) gauge group spontaneously broken to U ( 1 ) , our consideration is applicable to any gauge symmetry broken to some abelian subgroup.