Principles and physics program of γγ colliders

Such aspects of a physics program for photon-photon colliders as processes with production of heavy vector masons, Higgs bosons, and heavy quarks, integral relations between cross sections (sum rules) for various polarization states, hadron production processes, pomeron physics are discussed in brief. Emphasis is placed on nonlinear effects in the backward Compton scattering of photons of a circularly polarized laser wave focussed on a beam of longitudinally polarized ultrarelativistic electrons. The linear approximation in this conversion mechanism is also examined. Calibration processes for continuous monitoring of the gamma gamma collider luminosity and photon beam polarization are described. In this connection, production of two lepton pairs in the kinematics of narrow jets moving along the beam axis and production of a pair of charged leptons or bosons moving at large angles are considered. The results of numerical analyses are given.