Gamma-ray Limits on Neutrino Lines

TL;DR

This paper demonstrates that gamma-ray telescopes currently provide the most stringent limits on neutrino lines from dark matter annihilation for masses above 200 GeV, surpassing neutrino detectors.

Contribution

It shows gamma-ray data can set stronger constraints on neutrino lines from dark matter than neutrino detectors and highlights the potential to distinguish neutrino flavors.

Findings

Gamma-ray data impose the strongest limits for dark matter masses above 200 GeV.

Gamma-ray telescopes can differentiate neutrino flavors, unlike neutrino detectors.

Current gamma-ray observations already surpass neutrino detectors in sensitivity to neutrino lines.

Abstract

MMonochromatic neutrinos from dark matter annihilations ($\chi\chi\to \nu\bar\nu$) are always produced in association with a gamma-ray spectrum generated by electroweak bremsstrahlung. Consequently, these neutrino lines can be searched for not only with neutrino detectors but also indirectly with gamma-ray telescopes. Here, we derive limits on the dark matter annihilation cross section into neutrinos based on recent Fermi-LAT and HESS data. We find that, for dark matter masses above 200 GeV, gamma-ray data actually set the most stringent constraints on neutrino lines from dark matter annihilation and, therefore, an upper bound on the dark matter total annihilation cross section. In addition, we point out that gamma-ray telescopes, unlike neutrino detectors, have the potential to distinguish the flavor of the final state neutrino. Our results indicate that we have already entered into a new era where gamma-ray telescopes are more sensitive than neutrino detectors to neutrino lines from dark matter annihilation.