Light scalar mesons in photon–photon collisions

Discovered more than forty years ago and from the very start a stumbling block for the naive quark–antiquark model, light scalar mesons are virtually universally believed to be nontrivial in nature today. A major contribution to understanding the nature of light scalar mesons has come from the physics of photon–photon collisions, a field which has recently entered the era of high-precision statistics. In this paper, conclusions from current experimental data concerning the mechanisms of the two-photon creation of light scalar mesons are reviewed.