Random ballistic interpretation of the nonlinear guiding center theory of perpendicular transport

Nonlinear guiding center (NLGC) theory has been used to explain the asymptotic perpendicular diffusion coefficient k? of energetic charged particles in a turbulent magnetic field, which can be applied to better understand cosmic ray transport. Here we re-derive NLGC, replacing the assumption of diffusive decorrelation with random ballistic decorrelation (RBD), which yields an explicit formula for k?. We note that scattering processes can cause a reversal of the guiding center motion along the field line, i.e., 'backtracking,' leading to partial cancellation of contributions to k, especially for low-wavenumber components of themagnetic turbulence. We therefore include a heuristic backtracking correction (BC) that can be used in combination with RBD. In comparison with computer simulation results for various cases and two different magnetic field models (2D+slab and noisy RMHD), NLGC with RBD and BC provides a substantially improved characterization of the perpendicular diffusion coefficient for a fluctuation amplitude less than or equal to the large-scale magnetic field.