Unitarity constraints on chiral perturbative amplitudes

TL;DR

This paper reviews recent progress in applying unitarity constraints to chiral perturbation theory, highlighting the emergence of scalar resonances and their properties in a model-independent framework.

Contribution

It provides a model-independent review of how unitarity constraints influence chiral perturbation amplitudes and discusses properties of scalar resonances in related processes.

Findings

Scalar resonances are essential for fitting experimental data within unitarized chiral perturbation theory.

Recent progress includes a model-independent approach to unitarity constraints.

Studies reveal unique physical properties of low-lying scalar resonances.

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.