MHD Turbulence and Cosmic Ray Reacceleration in Galaxy Clusters

Cosmological MHD simulations of galaxy cluster formation show a significant amplification of seed magnetic fields. We developed a novel method to decompose cluster magnetized turbulence into modes and showed that the fraction of the fast mode is fairly large, around 1/4 in terms of energy. This is larger than that was estimated before, which implies that cluster turbulence interacts with cosmic rays rather efficiently. We propose a framework to deal with electron and proton reacceleration in galaxy clusters that includes feedback on turbulence. In particular, we establish a new upper limit on proton and electron fluxes based on turbulence intensity. These findings, along with detailed modeling of reacceleration, will help to reconcile the observed giant radio haloes and the unobserved diffuse gamma-ray emission from these clusters.