Radiative decays of φ meson and nature of light scalar resonances

We show on gauge invariance grounds that a new threshold phenomenon has been discovered in the radiative decays φ → γa0 → γπ0η and φ → γf0 → γπ0π0. This enables us to conclude that production of the light scalar mesons a0(980) and f0(980) in these decays is caused by the four-quark transitions, resulting in strong restrictions on the large-Nc expansions of the decay amplitudes. The analysis shows that these constraints give new evidence in favor of the four-quark nature of a0(980) and f0(980) mesons.