Spatial-Dependent Propagation of Cosmic Rays Results in Spectrum of Proton, Ratios of , B/C and Anisotropy of Nuclei

Abstract

Recent precise measurements of cosmic ray spectra revealed an anomalous hardening at ∼200 GV, observed by the ATIC, CREAM, PAMELA, and AMS02 experiments. Particularly, the latest observation of the <?MML p &macr; / p ratio by AMS02 demonstrated a flat distribution, which further validated the spectral anomalies of secondary particles. All those new phenomena indicated that the conventional propagation model of cosmic rays meets a challenge. In this work, the spatial-dependent diffusion coefficient <?MML D ( r , z , p ) is employed by tracing the source distribution under the physical picture of the two-halo model in the DRAGON package. Under such a scenario, the model calculation will result in two-component spectra for primary nuclei. Due to the smaller rigidity dependence of <?MML D ( r , z , p ) in the galactic disk, the ratios secondary-to-primary will inevitably be flatter and the expected anisotropy of cosmic rays will be much more attenuated than in the conventional model. As a result, we can reproduce the spectral hardening of protons, the flat ratios of <?MML p &macr; / p and B/C, and consistent anisotropy from ∼100 GeV to ∼100 TeV by only adopting one set of spatial-dependent diffusion coefficients <?MML D ( r , z , p ) in a galactic disk.

Revisit of cosmic ray antiprotons from dark matter annihilation with updated constraints on the background model from AMS-02 and collider data

“…Second, we assume a relatively simple propagation paradigm with a uniform diffusion coefficient. However, the actual case might be more complicated, as indicated by precise measurements of the CR spectra and diffuse γ-rays [32,53,54]. The impact of these alternative propagation configurations on the antiproton calculation deserves further detailed investigation.…”

Propagation of cosmic rays in the AMS-02 era

“…The diffusion coefficient may vary in the Milky Way due to different magnetic field distributions in the disk and halo (e.g., [45,46]). In particular, CRs may be confined much longer around the sources than expected due to non-linear self-generation of MHD waves via streaming instability [47].…”

On the knee of Galactic cosmic rays in light of sub-TeV spectral hardenings

“…However, remarkable spectral hardenings at an rigidity of a few hundred GV on the spectra of all major nuclei components were reported by the balloon-borne experiments ATIC-2 [25] and CREAM [26], and were confirmed with higher precision by the space detectors PAMELA [27] and AMS-02 [28,29]. Many kinds of models have been proposed to understand the origin of the spectral hardenings, including the super-position of different sources [30][31][32], the non-linear acceleration of the supernova remnant shocks [33,34], the re-acceleration mechanism when particles propagating in the Galaxy [35], and the spatially-dependent diffusion of CRs [36][37][38][39][40][41][42].…”

“…One possible physical explanation of the spectral hardening (β · log E) is the spatially-dependent diffusion of particles [36,39,41,42,50]. In a simplified version, i.e., CRs diffuse separately in the disk region and halo region (the two-halo model), the hardening of the primary CR nuclei and the excesses of secondary particles can be reasonably accounted for [36,41,42,50]. Here we extrapolate this model to the knee region to reproduce the results of the phenomenological "modified poly-gonato" model.…”

“…The propagation is confined in a halo with half height of z h . The diffusion coefficient, D xx , depends on both the spatial coordinates (r, z) and the particle rigidity, which is parameterized as [41]…”