Insights into $Q^2{\bar{Q}}^2$ states from an effective perspective

Ll. Ametller, P. Talavera

We discuss the two photon coupling of the lightest scalar meson on the basis of an extension of $\chi$PT. Using low energy data on the pion form-factor and the $\gamma \gamma \to {\pi }^{+}{\pi }^{-}({\pi }^0{\pi }^0)$…