Restricting UHECRs and cosmogenic neutrinos with Fermi-LAT

TL;DR

This paper demonstrates how recent Fermi-LAT measurements of diffuse gamma-ray background constrain models of ultrahigh energy cosmic rays and cosmogenic neutrino fluxes, limiting their detectability by current and future experiments.

Contribution

It provides new constraints on UHECR and neutrino models based on Fermi-LAT gamma-ray background data, impacting the prospects for neutrino detection.

Findings

Fermi-LAT data constrains UHECR models and reduces expected neutrino fluxes.

Models predicting detectable cosmogenic neutrinos are excluded by the new gamma-ray background measurements.

Next-generation neutrino detectors can only observe neutrinos under extreme model parameters.

Abstract

Ultrahigh energy cosmic ray (UHECR) protons interacting with the cosmic microwave background (CMB) produce UHE electrons and gamma-rays that in turn initiate electromagnetic cascades on CMB and infrared photons. As a result, a background of diffuse isotropic gamma radiation is accumulated in the energy range $E\lsim 100$ GeV. The Fermi-LAT collaboration has recently reported a measurement of the extragalactic diffuse background finding it less intense and softer than previously measured by EGRET. We show that this new result constrains UHECR models and the flux of cosmogenic neutrinos. In particular, it excludes models with cosmogenic neutrino fluxes detectable by existing neutrino experiments, while next-generation detectors as e.g. JEM-EUSO can observe neutrinos only for extreme parameters.