Non-resonant diagrams in radiative four-fermion processes

The complete tree level cross section for $e^+e^- \to e^- \bar\nu_e u \bar{d} \gamma$iscomputedanddiscussedincomparisonwiththecrosssectionsfor$e^+e^- \to e^- \bar\nu_e u \bar{d} $and$e^+e^- \to \bar{u} d u \bar{d}$. Event generators based on the GRACE package for the non-radiative and radiative case are presented. Special interest is brought to the effect of the non-resonant diagrams overlooked so far in other studies. Their contribution to the total cross section is presented for the LEP II energy range and for future linear colliders ($\sqrt{s}$ =500 GeV). Effects, at the W pair threshold, of order 3% ($e^{-}{\bar{\nu }}_{e}u\bar{d}$) and 27% ($\bar{u}du\bar{d}$) are reported. Similar behaviour for the radiative case is shown. At $\sqrt{s}$ = 500 GeV, the relative contribution of the non-resonant diagrams for the radiative channel reaches 42.5%.