Cosmic ray nuclei, antiprotons and gamma rays in the galaxy: a new diffusion model

We model the transport of cosmic ray nuclei in the galaxy by means of a new numerical code. At variance with previous numerical models, ours accounts for a generic spatial distribution of the diffusion coefficient. We found that in the case of radially uniform diffusion, the main secondary/primary ratios (B/C, N/O and sub-Fe/Fe) and the modulated antiproton spectrum consistently match the available observations. Convection and re-acceleration do not seem to be required in the energy range that we consider: 1 <= E <= 10(3) GeV/nucleon. We generalize these results, accounting for radial dependence of the diffusion coefficient, which is assumed to trace that of the cosmic ray sources. While this does not affect the prediction of secondary/primary ratios, the simulated longitude pro. le of the diffuse gamma-ray emission is significantly different from that for the uniform case and may agree with EGRET measurements without requiring invoking ad hoc assumptions on the galactic gas density distribution.