Neutral pion photoproduction on protons in fully covariant ChPT with Delta(1232) loop contributions

TL;DR

This paper investigates neutral pion photoproduction near threshold energies using covariant chiral perturbation theory, highlighting the importance of including the Delta(1232) resonance for better convergence and accurate low-energy constants.

Contribution

It introduces the Delta(1232) resonance as an explicit degree of freedom in covariant chiral perturbation theory for improved modeling of pion photoproduction.

Findings

Including Delta(1232) improves convergence

Low-energy constants align with literature

Model better describes near-threshold data

Abstract

We study the neutral pion photoproduction at near-threshold energies in fully covariant chiral perturbation theory up to O(p^3). When including only nucleonic virtual states in the model, the convergence is too slow. Therefore we test the model when introducing the Delta(1232) resonance as an additional degree of freedom. Some low-energy constants were fitted, converging to values in good agreement with those expected from literature.