Institute for Advanced Study / Princeton University Joint Astrophysics Colloquium

There has been a surge of interest within the particle-physics and dark matter communities in axions and axion-like particles (ALPs). These particles result from a possible extensions to the Standard Model that may solve the Strong-CP problem, and are further motivated by String Theory. Galaxy clusters are a superb laboratories for exploring ALP physics. Clusters are permeated by a magnetized hot intracluster medium (ICM) that can efficiently interconvert photons and ALPs. Here, I discuss how the transparency (or lack thereof) of the ICM to X-rays becomes a powerful way to constrain ALPs. I show that a careful examination of X-ray observations of cluster-hosted active galactic nuclei (AGN) by the Chandra X-ray Observatory allow the tightest constraints to date on ALP/photon coupling of ALPs in the low-mass regime (ALP masses less than ~peV). I finish by discussing the future prospects of these studies with the next generation X-ray observatories.