The cosmic triad: Cosmic rays, gamma-rays and neutrinos

Abstract

The existence of ultra-high energy (UHE) cosmic rays (CRs) with energies up to 100 EeV is a strong motivation for neutrino astronomy at the EeV energy scale. It seems unavoidable that UHE CRs undergo hadronic interactions with radiation backgrounds and ambient matter prior to their arrival at Earth. These interactions result in a flux of secondary neutrinos and γ-rays with energies up to a few percent of the initial CR energy. So far, no high-energy neutrino source could be unambiguously identified. We will review the various indirect neutrino limits that arise from the cosmic connection of UHE CRs, γ-rays and neutrinos. At the EeV energy scale the diffuse flux of cosmogenic neutrinos associated with the propagation of ultra-high energy cosmic rays in the cosmic radiation background seems to be the most promising candidate for a future detection. We will discuss its model dependence w.r.t. nuclear composition and evolution of the sources.