High-energy neutrinos from blazars: flux predictions with LeHa-Paris code and stacking analysis with KM3NeT/ARCA data

In the scenario of multi-messenger astronomy, high-energy neutrinos provide a unique probe of hadronic processes occurring in extreme astrophysical environments. These neutrinos are thought to originate from the same sources that accelerate cosmic rays, or from their surroundings, where sufficient matter or radiation fields allow part of the energy to be converted into secondary particles. Because they are neutral and weakly interacting, neutrinos can travel cosmological distances without absorption or deflection, preserving information about their origins. Their detection can therefore play a key role in identifying the sources of cosmic rays, even at the highest energies. For this purpose, large-scale neutrino telescopes are being constructed worldwide. The KM3NeT Collaboration, building on the experience of the ANTARES telescope, is deploying two Cherenkov neutrino detectors in the deep Mediterranean Sea: KM3NeT/ARCA and KM3NeT/ORCA. KM3NeT/ARCA, primarily dedicated to neutrino astronomy, will instrument a volume of about one cubic kilometer and will be sensitive to neutrinos from 100 GeV up to multi-PeV energies. Thanks to its modular design, it has already been collecting data during construction and is expected to significantly contribute to high-energy neutrino observations. This thesis focuses on searches for point-like sources of cosmic neutrinos with KM3NeT/ARCA, targeting blazars as potential extragalactic neutrino factories. Expected neutrino fluxes from high-frequency-peaked BL Lac objects are obtained by modeling the emission of PKS 2155-304 with the LeHa-Paris numerical code, which simulates radiative processes in relativistic jets and photo-meson interactions. This approach is extended to a larger source sample selected from the 3HSP catalogue. The resulting flux predictions are used as templates in stacking analyses based on binned likelihood methods, using data from several KM3NeT/ARCA configurations. Additionally, the detector performances in identifying point-like neutrino sources are investigated using time-integrated and time-dependent unbinned analysis techniques, laying the basis for more sensitive neutrino point source and flares searches.