Cosmic ray transport in anisotropic magnetohydrodynamic turbulence

Abstract

By calculating the heating rate of the interstellar medium a recent paper argued that the wave spectrum of the turbulent magnetic fields could be steeper than k -5/3 . Although this behaviour disagrees with the Kolmogorv theory of turbulence, a steep inertial range of the wave spectrum in the interstellar medium cannot be excluded by obervations. In this paper, we therefore explore the influence of steep spectra onto the momentum diffusion coefficient and onto the parallel mean free path of cosmic rays. The calculations presented in this paper use the quasilinear theory, which can be seen as the standard tool computing cosmic-ray diffusion coefficients. As in earlier papers we consider an anisotropic plasma-wave turbulence model. It is demonstrated that momentum and parallel spatial diffusion are quite different, if the inertial range spectral index is larger than the Kolmogorov value.