Pion axioproduction: The Delta resonance contribution

TL;DR

This paper analyzes pion axioproduction involving the Delta resonance using baryon chiral perturbation theory, revealing a mild isospin-breaking enhancement near the resonance that could inform axion search experiments.

Contribution

It introduces a novel analysis of axion-nucleon interactions via the Delta resonance within baryon chiral perturbation theory, incorporating the resonance in two distinct ways.

Findings

Partial wave cross section shows enhancement near the Delta resonance.

Isospin breaking reduces the expected enhancement.

Potential for new axion search strategies exploiting this effect.

Abstract

The process of pion axioproduction, $aN\to\pi N$, with an intermediate $\Delta$ resonance is analyzed using baryon chiral parturbation theory. The $\Delta$ resonance is included in two ways: First, deriving the $a\Delta N$-vertices, the axion is brought into contact with the resonance, and, second, taking the results of $\pi N$ elastic scattering including the $\Delta$, it is implicitly included in the form of a pion rescattering diagram. As a result, the partial wave cross section of axion-nucleon scattering shows an enhancement in the energy region around the $\Delta$ resonance. Because of the isospin breaking, the enhancement is not as pronounced as previously anticipated. However, since the isospin breaking here is much milder than that for usual hadronic processes, novel axion search experiments might still exploit this effect.