The cosmic-ray diffusion tensor in nonaxisymmetric turbulence

Previous investigations of magnetic field line random walk and charged particle transport in turbulence mostly employed an axisymmetric turbulence model. However, real turbulence is assumed to be nonaxisymmetric. In this article we employ a simple model for nonaxisymmetric turbulence based on a very recent article. By analytically describing the random walk of magnetic field lines and by combining these results with a general compound transport model, we derive the cosmic-ray diffusion tensor. As demonstrated, the nonaxisymmetry leads to different components of the cosmic-ray diffusion tensor in the perpendicular direction. These new results are essential for several applications such as solar modulation studies.