Charged Pion-Pair Production and Pion Polarizabilities to two Loops

TL;DR

This paper calculates the gamma gamma to charged pion pair production amplitude to two loops using chiral perturbation theory, estimates new coupling constants, and compares predictions with experimental data.

Contribution

It provides a detailed two-loop calculation of pion pair production and pion polarizabilities, including estimation of new coupling constants via resonance saturation.

Findings

Predictions align with experimental data

Estimated new coupling constants for chiral perturbation theory

Enhanced understanding of pion polarizabilities

Abstract

We evaluate the amplitude for gamma gamma --> pi^+ pi^- to two loops in the framework of chiral perturbation theory.The three new coupling constants that enter the result at this order in the low-energy expansion are estimated via resonance saturation. We discuss in addition the crossed channel processes gamma pi^+ --> gamma pi^+ - in particular the charged pion polarizabilities - to the same accuracy. The predictions are compared with available experimental information.