High energy photon-photon collisions

The collisions of high energy photons produced at a electron-positron collider provide a comprehensive laboratory for testing QCD, electroweak interactions and extensions of the standard model. The luminosity and energy of the colliding photons produced by back-scattering laser beams is expected to be comparable to that of the primary e+e- collisions. In this overview, we shall focus on tests of electroweak theory in photon-photon annihilation, particularly γγ → W+W-, γγ → Higgs bosons, and higher-order loop processes, such as γγ → γγ, Zγ and ZZ. Since each photon can be resolved into a W+Wminus pair, high energy photon-photon collisions can also provide a remarkably background-free laboratory for studying WW collisions and annihilation. We also review high energy γγ tests of quantum chromodynamics, such as the scaling of the photon structure function, t bar t production, mini-jet processes, and diffractive reactions