Fiorillo, Damiano Francesco Giuseppe (2021) Cosmic messengers as a tool to investigate astroparticle physics. [Tesi di dottorato]

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The recent observation by the IceCube experiment of neutrinos from outside the Solar System and potentially our Galaxy offers the possibility to investigate in detail many open questions in physics. On the one hand, it provides a guide to the determination of the astrophysical origin of the cosmic rays: in fact, while the latter are deflected by the Galactic magnetic fields before their arrival at Earth, neutrinos arrive to the Earth undeflected and unattenuated, therefore giving unprecedented information on their sites of origin. On the other hand, since the energies of astrophysical neutrinos are higher, and their path lengths are larger, than the ones attainable by any Earth-bound experiment, they are among the most sensitive probes of Beyond Standard Model (BSM) physics. In this thesis we highlight the potential of cosmic neutrinos along both these lines. In the first part of the thesis, we provide a review of the mechanisms underlying the production, propagation, and detection of the three main astrophysical messengers, namely cosmic-rays, gamma-rays, and neutrinos. In the second part, we provide a combined study of the IceCube neutrino data and the gamma-ray measurements by recent telescopes such as Fermi-LAT. We perform a multi messenger analysis, taking into account simultaneously neutrinos and gamma-rays, to obtain up-to-date constraints on the neutrino production in Starburst Galaxies. Furthermore, we propose a unified model able to describe neutrino production in photohadronic sources in terms of few parameters. This compact description allows us to express the sensitivity for detection of neutrino sources in terms of their astrophysical parameters, such as their magnetic field and their size. In the third part of this thesis, we show that high-energy neutrino and gamma-ray astronomy provides a powerful way of studying Beyond the Standard Model physics. We use the data from IceCube and Fermi-LAT to constrain extensions of the Standard Model which include dark matter decay, non-standard neutrino self-interactions, and violation of the equivalence principle.

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