Superfield perturbation theory in harmonic superspace

Superfield perturbation methods are developed for N = 2 supersymmetric theories in harmonic superspace with central charges. To illustrate our methods, explicit examples of loop calculations are given; the self-energies of the gauge hypermultiplet are computed at the one-loop level, giving the expected one-loop β function. It is also shown that the effective action may be written as integrals over a single d8theta in full superspace (but not in analytic subspace). The implication of this result is also briefly discussed