Searches for primary photons and neutrinos with the Pierre Auger Observatory

Abstract: The Pierre Auger Observatory stands as the largest detector for ultra-high-energy (UHE) cosmic rays. The Observatory is also sensitive to UHE photons and neutrinos that can be produced along with UHE cosmic rays or in top-down processes, such as the decay of dark matter particles. The search for these neutral particles relies on the hybrid measurements of extensive air showers, combining a fluorescence detector with a surface detector array and an underground muon detector. We present an overview of the searches for UHE photons and neutrinos utilizing data from the Pierre Auger Observatory. Currently, no photon or neutrino candidates have been identified. Consequently, we report on the most stringent limits to the integral UHE photon and neutrino fluxes above 50 PeV and 100 PeV, respectively, from diffuse and point-like steady sources. These limits led to strong constraints on theoretical models describing the cosmological evolution of the acceleration sites and the nature of dark-matter particles. Lastly, we briefly comment on the searches for these neutral particles in coincidence with gravitational wave events, underscoring the pivotal role of the Observatory in the context of multi-messenger astronomy at the highest energies.