Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints

TL;DR

This paper explores how high-energy gamma-ray observations and anisotropy measurements from EAS detectors can constrain PeV-scale decaying dark matter scenarios linked to IceCube neutrino fluxes, considering gamma-ray absorption effects.

Contribution

It introduces a method to use EAS detector anisotropy data to set limits on PeV-scale decaying dark matter, accounting for gamma-ray absorption and anisotropy features.

Findings

Current EAS anisotropy measurements constrain dark matter lifetime to about 10^{27} seconds.

Future gamma/hadron separation improvements can significantly tighten these constraints.

Absorption effects on gamma-ray propagation influence the detectability of dark matter decay signatures.

Abstract

The very high energy Galactic $\gamma$-ray sky is partially opaque in the ($0.1-10$) PeV energy range. In the light of the recently detected high energy neutrino flux by IceCube, a comparable very high energy $\gamma$-ray flux is expected in any scenario with a sizable Galactic contribution to the neutrino flux. Here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy $\gamma$-rays by the absorption on the cosmic microwave background photons and Galactic interstellar light. As a notable application of our considerations, we study the prospects of probing the PeV-scale decaying DM scenario, proposed as a possible source of IceCube neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular, we show that anisotropy measurements at EAS experiments are already sensitive to $\tau_{\rm DM}\sim {\cal O}(10^{27})$~s and future measurements, using better gamma/hadron separation, can improve the limit significantly.