Cosmic absorption of ultra high energy particles

TL;DR

This paper analyzes how ultra high energy particles interact with cosmic backgrounds, deriving their mean free paths and horizons, which are crucial for understanding their propagation limits in the universe.

Contribution

It provides the first calculation of the high energy neutrino horizon considering cosmic background neutrino scattering.

Findings

Derived mean free paths for photons, protons, and neutrinos.

Calculated the high energy neutrino horizon as a function of energy.

Discussed the interplay between energy loss length and mean free path for protons.

Abstract

This paper summarizes the limits on propagation of ultra high energy particles in the Universe, set up by their interactions with cosmic background of photons and neutrinos. By taking into account cosmic evolution of these backgrounds and considering appropriate interactions we derive the mean free path for ultra high energy photons, protons and neutrinos. For photons the relevant processes are the Breit-Wheeler process as well as the double pair production process. For protons the relevant reactions are the photopion production and the Bethe-Heitler process. We discuss the interplay between the energy loss length and mean free path for the Bethe-Heitler process. Neutrino opacity is determined by its scattering off the cosmic background neutrino. We compute for the first time the high energy neutrino horizon as a function of its energy.