Non-resonant diagrams in radiative four-fermion processes

The complete tree level cross section for e+e− → e−veudγ is computed and discussed in comparison with the cross sectionsfor e+e− → e−veud and e+e− → udud. Event generators based on the GRACE package for the non-radiative and radiative case are presented. Special interest is brought to the effect of the non-resonant diagrams overlooked so far in other studies. Their contribution to the total cross section is presented for the LEP II energy range and for future linear colliders (√s = 500 GeV). Effects, at the W pair threshold, of order 3% (e−veud) and 27% (udud) are reported. Similar behaviour for the radiative case is shown. At √s = 500 GeV, the relative contribution of the non-resonant diagrams for the radiative channel reaches 42.5%.