HIGH-ENERGY FACTORIZATION IN ELECTROWEAK PROCESSES

We propose to use high energy, k(perpendicular-to)-dependent, factorization (HEF) in electroweak fusion processes in order to systematically improve the effective W approximation (EWA) at collider energies. Starting from the example of top production, we show that HEF provides correctly all quasi constant terms in the production cross section, i.e. not only the ones O(1/M(W)2) which are typical of the EWA and are due to longitudinal polarizations of exchanged bosons, but also the ones O(1/M(t)2) which are partly due to transverse polarizations. It turns out that the latter contributions cannot be accounted for by collinear factorization only, but also come from longitudinal off-shell effects, typical of broken gauge theories, which are explicitly evaluated here.