Unitarity constraints on chiral perturbative amplitudes

Abstract

Low lying scalar resonances emerge as a necessary part to adjust chiral perturbation theory to experimental data once unitarity constraint is taken into consideration. I review recent progress made in this direction in a model independent approach. Also I briefly review studies on the odd physical properties of these low lying scalar resonances, including in the $\gamma \gamma \to {\pi }^{+}{\pi }^{-},{\pi }^0{\pi }^0$ processes.

Comments: Talk given at: International Workshop on Effective Field Theories: from the pion to the upsilon, February 2-6 2009, Valencia, Spain