Cosmic Ray Diffusion in Turbulent Magnetic Fields*

Cosmic-ray (CR) diffusion in turbulent and magnetized media is a fundamental problem in space physics and astrophysics. Motivated by the tensions between new-generation CR observations and existing theoretical paradigm of CR diffusion, we investigate new mechanisms of cosmic-ray (CR) diffusion in turbulent magnetic fields. Since the diffusion of CRs strongly depends on the properties of magnetohydrodynamic (MHD) turbulence, our improved understanding of MHD turbulence have laid the theoretical foundation for a new mechanism of CR diffusion known as mirror diffusion. The mirror diffusion of CRs highlights the importance of perpendicular superdiffusion and magnetic mirroring in MHD turbulence. Our numerical simulations demonstrate that the repeated 90-degree crossings of pitch angle due to mirror reflections enhance CR confinement. Mirror diffusion and scattering diffusion together result in a new Levy-flight-like propagation paradigm of CRs.