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

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(alpha gamma) greater than or similar to 3.9-7.8 x 10(-11) GeV-1 for m(a) less than or similar to 4 x 10(-7) 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.

Automated summary

The detection of high-energy neutrinos supports the existence of gamma rays from cosmic accelerators. The interaction between photons and ultra-light axion-like particles (ALPs) allows for the conversion of ALPs into high-energy photons. The recent observations from LHAASO provide evidence for the existence of this conversion process. This new result is important for our understanding of the universe and fundamental particle physics.