Theory of high-energy messengers

TL;DR

This paper reviews the theoretical understanding of high-energy cosmic messengers like photons, cosmic rays, neutrinos, and gravitational waves, emphasizing their origins, propagation, and detection prospects in the extragalactic universe.

Contribution

It synthesizes current theories on high-energy messengers, compares observational data, and discusses potential astrophysical sources, providing a comprehensive overview of the field.

Findings

Comparison of photon and UHECR intensities in space

Detection of high-energy neutrinos by IceCube

Identification of candidate sources like active galaxies

Abstract

Knowledge of the distant high-energy universe comes from photons, ultra-high energy cosmic rays (UHECRs), high-energy neutrinos, and gravitational waves. The theory of high-energy messengers reviewed here focuses on the extragalactic background light at all wavelengths, cosmic rays and magnetic fields in intergalactic space, and neutrinos of extragalactic origin. Comparisons are drawn between the intensities of photons and UHECRs in intergalactic space, and the high-energy neutrinos recently detected with IceCube at about the Waxman-Bahcall flux. Source candidates for UHECRs and high-energy neutrinos are reviewed, focusing on star-forming and radio-loud active galaxies. HAWC and Advanced LIGO are just underway, with much anticipation.