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

We calculate the amplitudes of the axion photoproduction off the nucleon, i.e., γ N → 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 aγγ 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 γ N → a N processes manifest distinct behaviors in the total and differential cross sections, which could provide useful quantities to distinguish different axion models.