Exact propagators in harmonic superspace

Within the background field formulation in harmonic superspace for quantum N=2 super-Yang-Mills theories, the propagators of the matter, gauge and ghost superfields possess a complicated dependence on the SU(2) harmonic variables via the background vector multiplet. This dependence is shown to simplify drastically in the case of an on-shell vector multiplet. For a covariantly constant background vector multiplet, we exactly compute all the propagators. In conjunction with the covariant multi-loop scheme developed in hep-th/0302205, these results provide an efficient (manifestly N=2 supersymmetric) technical setup for computing multi-loop quantum corrections to effective actions in N=2 supersymmetric gauge theories, including the N=4 super-Yang-Mills theory