Problem of scalar mesons

A review is dedicated to a study of scalar mesons which manifest a number of features which are unusual for a quark-antiquark system. The present data on these resonances are analyzed by a rather general method which is the most adequate one to test the different suggestions on a dynamical structure of resonances. It is shown that the most suitable model for a description of the known scalar mesons is the qq antiq anti q model. One cannot identify any known scalar meson with the gluonium. The questions are studied of an ambiguity in the behaviour of ππ-scattering s wave phase shift and S*, delta0, resonance mixing which are independent of concrete models for scalar resonances. A number of new experiments is suggested, which could give the worth information of the scalar meson structure. In particular, a bright manifestation of S*(980) and epsilon(1400) resonances in the π+π- → eta eta process in predicted from the analysis of ππ → K anti K, ππ → ππ processes