A comprehensive study of axion photoproduction off the nucleon in chiral effective field theory

Abstract

We calculate the amplitudes of the axion photoproduction off the nucleon, i.e., $\gamma N \to a N$, within the framework of chiral effective field theory. Several different types of contributions are simultaneously included in our calculation, namely the nucleon exchanges up to next-to-leading order, the $a\gamma\gamma$ vertex and the vector meson exchanges in the $t$-channel. We utilize the existing hadronic inputs as much as possible to fix the unknown couplings. A comprehensive study of the phenomenological discussions is then provided in this work. Different mechanisms in the $\gamma N \to a N$ processes manifest distinct behaviors in the total and differential cross sections, which could provide useful quantities to distinguish different axion models.