Solution to the cosmic ray anisotropy problem

Understand

In the standard diffusive picture for transport of cosmic rays (CRs), a gradient in the CR density induces a typically small, dipolar anisotropy in their arrival directions.

• This has been widely advertised as a tool for finding nearby sources.
• However, the predicted dipole amplitude at TeV and PeV energies exceeds the measured one by almost two orders of magnitude.
• Here, we critically examine the validity of this prediction which is based on averaging over an ensemble of turbulent magnetic fields.