Micromirror confinement of sub-TeV cosmic rays in galaxy clusters

Recent observations reveal that cosmic rays (CRs) are more tightly confined in various astrophysical systems (e.g. radio bubbles) than current theories predict. I show that microscale magnetic fluctuations, particularly from the mirror instability, significantly influence CR transport. Our theory is supported by simulations of CRs in the intracluster medium (ICM) of galaxy clusters. Our results indicate that sub-TeV CR confinement in the ICM is much more efficient than previously thought based on extrapolating existing Galactic-transport theories.