We explore the problems of propagation, confinement, and anisotropy of ultrahigh-energy cosmic rays. Previous investigations of plasma-particle interactions are based on a first-order perturbation theory also known as quasilinear theory. It is the subject of this article to employ a nonlinear diffusion theory, namely, the second-order quasilinear theory. We compute the parallel mean free path for slab and for isotropic turbulence for a wave spectrum with small-wave-number cutoff. It is demonstrated that we obtain a finite parallel mean free path even if the Larmor radius of the charged particle is larger than the largest scale of turbulence. Therefore, charged cosmic rays of all energies can be scattered and confined to the Galaxy by the turbulent magnetic fields.

• Received 2 April 2009

DOI:https://doi.org/10.1103/PhysRevD.80.023012