Radiative corrections toZZ→ZZin the electroweak standard model

The cross section for $\mathrm{ZZ}\to \mathrm{ZZ}$ with arbitrarily polarized $Z$ bosons is calculated within the electroweak standard model including the complete $O\left(\alpha \right)$ corrections. We show the numerical importance of the radiative corrections and elaborate its characteristic features. The treatment of the Higgs-boson resonance is discussed in different schemes including the $S$-matrix-motivated pole scheme and the background-field method. The numerical accuracy of the equivalence theorem is investigated by comparing the cross sections for purely longitudinal $Z$ bosons obtained from the equivalence theorem and from the complete calculation. In this context the full $O\left(\alpha \right)$ corrections are also confronted with the enhanced corrections of $O\left(\alpha M_H^2{/s}_W^2{M}_W^2\right),$ which were frequently used in the literature.