Description of e^-e^+toγγ, Z γ, ZZ in SM and MSSM

We present a complete analysis of the one loop electroweak corrections to $e^-e^+\to\gamma\gamma, ~Z\gamma, ~ZZ$ in the Standard (SM) and the Minimal Supersymmetric Standard Model (MSSM). Analytic expressions are written for the contributions to the helicity amplitudes. Several observables accessible for polarized or unpolarized beams and transverse, longitudinal or unpolarized final states are computed. We show that in the few hundred GeV region, these observables provide a test of the various SM or MSSM components. For the dominant TT amplitude at high energy, the sensitivity to the details of the various sectors disappears, but the energy dependence fixed by leading logarithmic contributions, provides a model independent signature discriminating SM from MSSM. Subdominant TL or LL amplitudes though, remain sensitive to the details of the SM or MSSM sectors. Numerical illustrations are given for energies up to several TeV. The analysis may also be used to search for new physics characterized by anomalously strong interactions among the neutral gauge bosons.