Origin of the Cosmic Ray Spectral Hardening

TL;DR

This paper proposes that the observed spectral hardening of cosmic rays above 100 GeV is due to spatial variations in their propagation properties within the Galaxy, challenging traditional models.

Contribution

It introduces a model where the diffusion coefficient varies spatially, successfully explaining the spectral hardening observed in cosmic ray data.

Findings

Reproduces cosmic ray spectral hardening with a non-separable diffusion coefficient.

Suggests spatial variation in cosmic-ray transport properties as a key factor.

Implications for cosmic-ray acceleration and propagation physics.

Abstract

Recent data from ATIC, CREAM and PAMELA indicate that the cosmic ray energy spectra of protons and nuclei exhibit a remarkable hardening at energies above 100 GeV per nucleon. We propose that the hardening is an interstellar propagation effect that originates from a spatial change of the cosmic-ray transport properties in different regions of the Galaxy. The key hypothesis is that the diffusion coefficient is not separable into energy and space variables as usually assumed. Under this scenario, we can reproduce the observational data well. Our model has several implications for the cosmic-ray acceleration/propagation physics and can be tested by ongoing experiments such as the Alpha Magnetic Spectrometer or Fermi/LAT.