37 Years with the light scalar mesons. The learned lessons

Attention is paid to the production mechanisms of light scalars that reveal their nature. We reveal the chiral shielding of the σ(600) meson. We show that the kaon loop mechanism of the ϕ radiative decays, ratified by experiment, is four-quark transition and points to the four-quark nature of light scalars. We show also that the light scalars are produced in the two photon collisions via four-quark transitions in contrast to the classic P wave tensor qq̅ mesons that are produced via two-quark transitions γγ → qq̅. We study the mechanism of production of the light scalar mesons in the D⁺ _s → π⁺π⁻ e ⁺ν decays: D⁺ _s → ss̅e ⁺ν → [σ(600) + f ₀(980)]e ⁺ν → π⁺π⁻ e ⁺ν, and compare it with the mechanism of production of the light pseudoscalar mesons in the D⁺ _s → (η/η′)e ⁺ν decays: D⁺ _s → ss̅e ⁺ν → (η/η′)e ⁺ν. As a result we find support to four-quark nature of light scalars. In the end, we outline the future research program.