Threshold pion electro- and photoproduction off nucleons in covariant chiral perturbation theory

TL;DR

This paper investigates pion electro- and photoproduction near threshold using covariant baryon chiral perturbation theory with explicit $$ resonance inclusion, improving data agreement and model convergence.

Contribution

It introduces a covariant chiral perturbation theory approach with explicit $$ resonance, enhancing accuracy and convergence in pion production modeling.

Findings

Explicit $$ resonance inclusion improves data fit.

Model convergence is significantly enhanced.

Low energy constants are fitted to experimental data.

Abstract

Pion electro- and photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O($p^3$) in the extended-on-mass-shell scheme, with the explicit inclusion of the $\Delta(1232)$ resonance. The relevant low energy constants are fixed by fitting the available experimental data with the theoretical model. The inclusion of the $\Delta$ resonance as an explicit degree of freedom substantially improves the agreement with data and the convergence of the model.