Diffusion of Cosmic Rays in MHD Turbulence with Magnetic Mirrors

As the fundamental physical process with many astrophysical implications, the diffusion of cosmic rays (CRs) is determined by their interaction with magnetohydrodynamic (MHD) turbulence. We consider the magnetic mirroring effect arising from MHD turbulence on the diffusion of CRs. Due to the intrinsic superdiffusion of turbulent magnetic fields, CRs with large pitch angles that undergo mirror reflection, i.e., mirroring CRs, are not trapped between magnetic mirrors, but move diffusively along the turbulent magnetic field, leading to a new type of parallel diffusion, i.e., mirror diffusion. This mirror diffusion is in general much slower than the diffusion of CRs with small pitch angles that undergo gyroresonant scattering. We find that the mirror diffusion of CRs is important for confining CRs in star-forming regions and their strong coupling with the interstellar media in active galaxies.