Researchers examined how the neutron-star-cooling limit on the QCD axion mass (KSVZ and DFSZ models) changes when heavier particles such as hyperons and Delta resonances are allowed in the core. The dependence is generally mild, reinforcing the known limit, though in the DFSZ case it may bring the limit into IAXO's sensitivity window.

— via arXiv — Astro-ph, Fernando Arias-Arag'on, Federico Nola