Advancing the phenomenology of GeV-scale axion-like particles

Abstract: Searches for axion-like particles (ALPs) with masses in the GeV range are a central objective of present and future Intensity-Frontier experiments. Interpreting these searches demands a reliable description of ALP production and decay. The prescription currently adopted by the community depends on unphysical chiral-rotation parameters, wrongly describes the mass scaling of the ALP flux, and ignores mixing with heavy pseudoscalar resonances. We introduce the framework that treats GeV-scale ALP interactions self-consistently, includes their mixing with heavier excitations $\pi(1300)$, $\eta(1295)$, $\eta(1440)$, and properly describes production channels. When applying our description to proton beam experiments, we find that existing bounds and projected sensitivities shift by up to an order of magnitude relative to earlier estimates. We further delineate the dominant theoretical uncertainties, which originate from the still-incomplete experimental knowledge of the light-meson spectrum.