Non-factorizable corrections to W-pair production: Methods and analytic results

In this paper we present two methods to evaluate non-factorizable corrections to pair-production of unstable particles. The methods are illustrated in detail for W-pair-mediated four-fermion production. The results are valid a few widths above threshold, but not at threshold. One method uses the decomposition of n-point scalar functions for virtual and real photons, and can therefore be generalized to more complicated final states than four fermions. The other technique is an elaboration on a method known from the literature and serves as a useful check. Applications to other processes than W-pair production are briefly mentioned. (orig.)