Supernova limits on QCD axionlike particles

In this paper, we explore the phenomenology of massive axionlike particles (ALPs) coupled to quarks and gluons, dubbed "QCD ALPs," with an emphasis on the associated low-energy observables. ALPs coupled to gluons and quarks not only induce nuclear interactions at scales below the QCD scale, relevant for ALP production in supernovae (SNe), but naturally also couple to photons similarly to the QCD axion. We discuss the link between the high-energy formulation of ALP theories and their effective couplings with nucleons and photons. The induced photon coupling allows ALPs with masses $m_a\gtrsim 1\mathrm{MeV}$ to efficiently decay into photons, and astrophysical observables severely constrain the ALP parameter space. We show that a combination of arguments related to SN events rule out ALP-nucleon couplings down to $g_{aN}\gtrsim {10}^{-11}–{10}^{-10}$ for $m_a\gtrsim 1\mathrm{MeV}$—a region of the parameter space that was hitherto unconstrained.