Low-energy next-to-leading contributions to the effective action in {cal N}=4 SYM theory

Using formulation of ${\cal N}=4$ SYM theory in terms of ${\cal N}=1$ superfields superfields we construct the derivative expansion of the one-loop ${\cal N}=4$ SYM effective action in background fields corresponding to constant Abelian strength $F_{mn}$ and constant hypermultiplet. Any term of the effective action derivative expansion can be rewritten in terms of ${\cal N}=2$ superfields. The action is manifestly ${\cal N}=2$ supersymmetric but on-shell hidden ${\cal N}=2$ supersymmetry is violated. We propose a procedure which allows to restore the hidden ${\cal N}=2$ invariance.