Recent developments in chiral perturbation theory

TL;DR

This paper reviews recent progress in chiral perturbation theory, highlighting challenges in precision predictions for certain processes and successes in others like pi pi scattering through advanced theoretical methods.

Contribution

It provides an overview of the current status of chiral perturbation theory, emphasizing the difficulties and achievements in improving predictive accuracy.

Findings

CHPT struggles to improve accuracy for K_L -> pi^0 gamma gamma

Two-loop CHPT combined with dispersion relations yields precise pi pi scattering predictions

Higher-order CHPT has limited impact on certain complex decay processes

Abstract

I briefly review the current status of chiral perturbation theory in the meson sector. Emphasis is given on the quest for higher precision. I discuss two examples: one where it is difficult to make a good prediction (K_L -> pi^0 gamma gamma), and where CHPT, even when pushed to higher orders, cannot yield an increase in accuracy. The second one is pi pi scattering where a very sharp prediction can be made by combining CHPT at the two-loop level with dispersion relations