Abstract :
We show on gauge invariance grounds that the fine threshold phenomenon is discovered in the radiative decays φ→γa0→γπ0η and φ→γf0→γπ0π0. This enables to conclude that production of the lightest 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 evidences in favor of the four-quark nature of a0(980) and f0(980) mesons.
