Astrofisica Multimessenger all'Osservatorio Pierre Auger

Cosmogenic neutrinos are expected to originate in the extragalactic propagation of ultra-high-energy cosmic rays (UHECRs), as a result of their interactions with background photons. Due to these reactions, the visible Universe in UHECRs is more limited than in neutrinos, which instead could reach us without interacting after traveling cosmological distances. In this thesis, we exploit a multimessenger approach by computing the expected energy spectrum and mass composition of UHECRs at Earth corresponding to combinations of spectral parameters and mass composition at their sources, as well as parameters related to the UHECR source distribution, and by determining, at the same time, the associated cosmogenic neutrino fluxes. By comparing the expected UHECR observables to the energy spectrum and mass composition measured at the Pierre Auger Observatory above $10^{17.8}$~eV and the expected neutrino fluxes to the most updated neutrino limits, we show the dependence of the neutrino fluxes on the characteristics of the properties of the potential sources of UHECRs, such as their cosmological evolution and maximum redshift. Furthermore, the fraction of protons compatible with UHECR data is also investigated in terms of expected neutrino fluxes. In addition, we investigate the energy region in which the transition from galactic to extragalactic origin of the cosmic rays is expected to happen. For this purpose, the analysis has been extended to $\sim 10^{17}$~eV, including a galactic component. An extension to lower energies could help to pinpoint the properties of the galactic-to-extragalactic transition.