Constraining axion-like particles with the diffuse gamma-ray flux measured by the Large High Altitude Air Shower Observatory

TL;DR

This paper uses diffuse gamma-ray flux measurements by LHAASO to set new constraints on axion-like particles, demonstrating how photon-ALP mixing affects high-energy gamma-ray propagation and detection.

Contribution

It introduces a novel method to constrain ALP-photon coupling using diffuse gamma-ray flux data from LHAASO, extending existing bounds in the low-mass ALP regime.

Findings

Excluded ALP-photon coupling g_{aγ} > 3.9-7.8 × 10^{-11} GeV^{-1} at 95% CL for m_{a} < 4×10^{-7} eV.

Provided complementary bounds to existing gamma-ray ALP constraints.

Highlighted the role of photon-ALP mixing in high-energy gamma-ray propagation.

Abstract

The detection of very high-energy neutrinos by IceCube experiment supports the existence of a comparable gamma-ray counterpart from the same cosmic accelerators. Under the likely assumption that the sources of these particles are of extragalactic origin, the emitted photon flux would be significantly absorbed during its propagation over cosmic distances. However, in the presence of photon mixing with ultra-light axion-like-particles (ALPs), this expectation would be strongly modified. Notably, photon-ALP conversions in the host galaxy would produce an ALP flux which propagates unimpeded in the extragalactic space. Then, the back-conversion of ALPs in the Galactic magnetic field leads to a diffuse high-energy photon flux. In this context, the recent detection of the diffuse high-energy photon flux by the Large High Altitude Air Shower Observatory (LHAASO) allows us to exclude at the $95\%$ CL an ALP-photon coupling $g_{a\gamma}\gtrsim 3.9-7.8 \times 10^{-11}~\mathrm{GeV^{-1}}$ for $m_{a}\lesssim 4\times10^{-7}~\mathrm{eV}$, depending on the assumptions on the magnetic fields and on the original gamma-ray spectrum. This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and sensitivities of future experiments.