Non-linear cosmic ray Galactic transport in the light of AMS-02 and Voyager data

TL;DR

This paper demonstrates that cosmic ray spectra and ratios measured by AMS-02 and Voyager are well explained by a model where CRs propagate via self-generated waves, revealing a spectral break and low-energy advection effects.

Contribution

The study provides strong evidence that self-generated waves dominate cosmic ray transport, explaining spectral features and low-energy behavior without free parameters.

Findings

Spectral break at a few hundred GV due to transition in wave regimes

Good agreement with Voyager and AMS-02 data on proton and helium spectra

CRs below a few GV are advected with self-generated waves at Alfvén speed

Abstract

Context: Features in the spectra of primary cosmic rays (CRs) provide invaluable information on the propagation of these particles in the Galaxy. In the rigidity region around a few hundred GV, such features have been measured in the proton and helium spectra by the PAMELA experiment and later confirmed with a higher significance by AMS-02. We investigate the implications of these datasets for the scenario in which CRs propagate under the action of self-generated waves. Aims: We show that the recent data on the spectrum of protons and helium nuclei as collected with AMS-02 and Voyager are in very good agreement with the predictions of a model in which the transport of Galactic CRs is regulated by self-generated waves. We also study the implications of the scenario for the boron-to-carbon ratio: although a good overall agreement is found, at high energy we find marginal support for a (quasi) energy independent contribution to the grammage, that we argue may come from the sources themselves Results: A break in the spectra of all nuclei is found at rigidity of a few hundred GV, as a result of a transition from self-generated waves to pre-existing waves with a Kolmogorov power spectrum. Neither the slope of the diffusion coefficient, nor its normalisation are free parameters. Moreover, at rigidities below a few GV, CRs are predicted to be advected with the self-generated waves at the local Alfv\'en speed. This effect, predicted in our previous work, provides an excellent fit to the Voyager data on the proton and helium spectra at low energies, providing additional support to the model.