Ultra High Energy Cosmic Rays Diffusion in an Expanding Universe

TL;DR

This paper compares the diffusion of ultra-high energy cosmic rays in expanding versus static universes, revealing significant discrepancies that depend on parameter choices.

Contribution

It provides a formal comparison between diffusion solutions in expanding and static universes, highlighting the impact of cosmic expansion on cosmic ray propagation.

Findings

Discrepancies between solutions are significant with identical parameters.

Differences diminish when best-fit parameters are adjusted for each model.

Expanding universe effects are crucial for accurate cosmic ray diffusion modeling.

Abstract

We study the solution of the diffusion equation for Ultra-High Energy Cosmic Rays in the general case of an expanding universe, comparing it with the well known Syrovatsky solution obtained in the more restrictive case of a static universe. The formal comparison of the two solutions with all parameters being fixed identically reveals an appreciable discrepancy. This discrepancy is less important if in both models a different set of best-fit parameters is used.