Ponente
Descripción
The transition from diffusion to gradient-curvature drift as the dominant mechanism for the Galactic escape of cosmic rays (CRs) is considered a possible origin of the CR “knee". We studied the connection between antisymmetric diffusion and these drifts by performing test-particle simulations of CR propagation in synthetic turbulent magnetic fields using the Monte Carlo code CRPropa 3. We computed the drift escape timescale in realistic Galactic magnetic field configurations as a function of particle rigidity and magnetic turbulence level, and we compared it to the escape timescales by parallel and perpendicular diffusion. We found that for low turbulence levels and large Galactic halo lengths, a "knee"-like spectral feature is predicted, attributed to the onset of drifts over perpendicular diffusion. To evaluate the effectiveness of this model, we estimated the predicted CR grammage at the “knee” energy range under this model and compared it to the grammage inferred from measurements of B/C ratio at TeV energies. We discuss how a energy-independent gramme at high-energies could lead to a good agreement between the model and direct CR observations. Alternatively, we explored how a topology of the regular magnetic field enhancing parallel and perpendicular diffusion could reproduce the observed grammage at low-energies while preserving a diffusion-drift transition at PeV energies.
