Gamma-ray production in the cosmic-ray -- dark matter scattering as a probe of the axion-like particle -- proton interaction

TL;DR

This paper explores how very-high-energy gamma-ray observations can be used to detect interactions between cosmic-ray protons and axion-like particles in dark matter halos, offering a new way to probe ALP properties.

Contribution

It demonstrates that ground-based gamma-ray observatories can effectively probe ALP-proton couplings in unexplored mass ranges, including models related to QCD axion dark matter.

Findings

Ground-based gamma-ray telescopes can reach sensitivities to ALP-proton couplings above 10^{-2}.

The method probes ALP masses from 1 eV to 10^8 eV, surpassing other astrophysical constraints.

Potential to test QCD axion dark matter models like KSVZ and DFSZ within the MeV mass range.

Abstract

The production of very-high-energy (VHE, $E_{\gamma} \gtrsim 100$ GeV) gamma rays resulting from the scattering of high-energy cosmic-ray protons off axion-like particles (ALPs) populating the dark matter halo of the Milky Way is investigated. By employing the latest instrument response functions for current and future facilities, we demonstrate that ground-based VHE gamma-ray observatories, such as H.E.S.S., CTAO, and SWGO, provide a promising and complementary avenue to probe the yet uncharted ALP-proton coupling $g_{ap}$. Our results show that these experiments can reach sensitivity to couplings above $10^{-2}$ in the $1 - 10^{8}$ eV ALP mass range, a region that remains largely unexplored by supernova and neutron star cooling observations. Interestingly, we demonstrate that this search channel is capable of probing QCD axion dark matter models, assuming two benchmark models for it: the Kim-Shifman-Vainshtein-Zakharov (KSVZ) Dine-Fischler-Srednicki-Zhitnitsky (DFSZ) models, specifically within the MeV mass range. These findings highlight the potential of VHE gamma-ray astronomy to provide unique constraints on the interaction between ALPs and the baryonic sector.