Speaker
Description
The detection of very high-energy neutrinos by the 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 extra-galactic origin, even for transparent sources the 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 source would produce an ALP flux which propagates unimpeded in the extra-galactic space without being absorbed. 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 $g_{a\gamma}> 3.0-6.0 \times 10^{-11}~\mathrm{GeV^{-1}}$ for $m_{a}< 4\times 10^{-7}~\mathrm{eV}$, depending on the magnetic field in the source and on the original gamma-ray spectrum.This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and the sensitivity of future experiments.
