The equivalent vector boson approximation at threshold energies

A simple derivation of the distributions of the equivalent electroweak vector bosons in leptons and quarks is presented. The applicability of the equivalent vector boson approximation at relatively low energies close to the $W$ and $Z$ boson thresholds is demonstrated. It is shown that the threshold correction to the distribution functions emerges naturally in the theory. Implications of the results for processes with the emission of the gauge bosons are discussed.