Axion Dark Matter from Heavy Quarks

Abstract

We propose simple scenarios where the observed dark matter abundance arises from decays and scatterings of heavy quarks through freeze-in of an axion-like particle with mass in the $10\mathrm{keV}-1\mathrm{MeV}$ range. These models can be tested by future X-ray telescopes, and in some cases will be almost entirely probed by searches for two-body decays $K\to \pi +invis.$ at NA62. As a byproduct, we discuss the cancellation of IR divergencies in flavor-violating scattering processes relevant for thermal axion production, and derive the general contribution to axion-photon couplings from all three light quarks.

Comments: 9 pages + appendix