A Critical Examination of the Nested Leaky Box Model for Galactic Cosmic Ray Transport

TL;DR

This paper critically evaluates the nested leaky box model for galactic cosmic ray transport, finding it inconsistent with current observations and suggesting alternative regions for cosmic ray grammage accumulation.

Contribution

It provides a detailed critique of the nested leaky box model and explores the possibility of cosmic ray grammage being accumulated near sources instead of the interstellar medium.

Findings

The model conflicts with observational data on cosmic-ray spectra.

The standard version of the model is effectively ruled out by current data.

Alternative hypotheses about grammage accumulation are proposed for future investigation.

Abstract

We revisit the predictions of the nested leaky box model in detail, in terms of both primary cosmic-ray spectra, spectra of stable and unstable nuclei and antimatter production (positrons and antiprotons). We conclude that the model is in direct conflict with several observational facts and at least in its vanilla version should be considered as ruled out by current data. We also speculate on some possibly interesting implications of the idea that at least a fraction of Galactic grammage may not be accumulated in the journey of cosmic rays in the interstellar medium but rather inside the sources or in regions around them. These speculations will become increasingly more relevant with the higher precision data becoming available at high energies.