Light fermion mass effects in e+e−1 → 4 fermions

We investigated the effect of the light fermion masses on cross sections for e+e− → 4 fermions in the fermion loop scheme defined by W. Beenakker et al. [NIKHEF-96-031 (1996), hep/ph-9612260], and approximations to it. The effects are found to be very small, except of course in the collinear region of single W boson production where the electron mass acts as the cut-off.