Calculation of Two-Boson Exchange with Complex-Valued Masses

new method for calculating the contribution of two-boson exchange diagrams (boxes) to the cross section for a four fermion process that involve one and two complex-valued boson masses is described. A detailed numerical analysis of the results obtained by means of this method and their comparison with the asymptotic expressions for the above cross section in the regions of energies below and above the Z -resonance energy are performed.