Cosmic-ray transport from AMS-02 boron to carbon ratio data: Benchmark models and interpretation

This article aims at establishing new benchmark scenarios for Galactic cosmic-ray propagation in the GV-TV rigidity range, based on fits to the AMS-02 boron to carbon ratio (B/C) data with the USINE V3.5 propagation code. We employ a new fitting procedure, cautiously taking into account data systematic error correlations in different rigidity bins and considering Solar modulation potential and leading nuclear cross section as nuisance parameters. We delineate specific low, intermediate, and high-rigidity ranges that can be related to both features in the data and peculiar microphysics mechanisms resulting in spectral breaks. We single out a scenario which yields excellent fits to the data and includes all the presumably relevant complexity, the BIG model. This model has two limiting regimes: (i) the SLIM model, a minimal diffusion-only setup, and (ii) the QUAINT model, a convection-reacceleration model where transport is tuned by nonrelativistic effects. All models lead to robust predictions in the high-energy regime (greater than or similar to 10 GV), i.e., independent of the propagation scenario: at 1 sigma, the diffusion slope delta is [0.43-0.53], whereas K-10, the diffusion coefficient at 10 GV, is [0.26-0.36] kpc(2) Myr(-1); we confirm the robustness of the high-energy break, with a typical value Delta(h) similar to 0.2. We also find a hint for a similar (reversed) feature at low rigidity around the B/C peak (similar to 4 GV) which might be related to some effective damping scale in the magnetic turbulence.