Non-conserved currents and gauge-restoring schemes in single W production

We generalize the inclusion of the imaginary parts of the fermionic one-loop corrections for processes with unstable vector bosons to the case of massive external fermions and non conservation of weak currents. We study the effect of initial and final state fermion masses in single W production in connection with the gauge-invariant treatment of the finite-width effects of W and Z bosons, giving numerical comparisons of different gauge-invariance-preserving schemes in the energy range of LEP2 and LC for e(-)e(+) --> e(-)<(nu)over bar>(e)u (d) over bar. We do not find significant differences between the results obtained in the imaginary part fermion loop scheme and in other exactly gauge preserving methods. (C) 2000 Elsevier Science B.V. All rights reserved.