Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields

Markus Ahlers

Published 2013-10-21, updated 2014-01-15Version 2

The propagation of cosmic rays (CRs) in turbulent interstellar magnetic fields is typically described as a spatial diffusion process. This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative background flow. We show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution. These "anomalous" anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent magnetic field. We show that the predictions of this model are in excellent agreement with the observed power spectrum of multi-TeV CRs.