PhD defense by Victor Valera

The particle physics discovery potential in the ultra-high-energy neutrino era

This thesis discusses ultra-high-energy (UHE) neutrinos, in particular, the near-future realization, long-awaited, of their potential to probe astrophysics and particle physics in the EeV energy range (10^{18} eV) for the first time. These neutrinos offer a unique and unobstructed view of the most energetic and distant astrophysical events in a Universe where high-energy cosmic rays and gamma rays face hindrances due to opacity and magnetic fields. At the same time, they provide access to particle process that occur at energies orders of magnitude higher than in present and envisioned particle accelerators.

Today, more than fifty years after first being proposed, UHE neutrinos remain undiscovered because of their low flux, but perhaps not for much longer thanks to new upcoming detectors currently under planning and construction. We combine theoretical models of the neutrino flux, state-of-the-art detector simulations, and large-scale Bayesian statistical analysis to explore the transformative potential of UHE neutrinos, including the impact of experimental designs, resolution, and background contamination.

Our results validate the capability of upcoming UHE neutrino telescopes---in particular, of the radio array of the planned IceCube-Gen2, one of the largest planned---to discover the diffuse UHE neutrino flux and, simultaneously, to measure the neutrino-nucleon cross section at ultra-high energies for the first time. They also showcase physics opportunities that the discovery of EeV neutrinos can unlock, such as identifying point neutrino sources and constraining features of their population, and detecting heavy dark matter via its decay into neutrinos. Across the board, our results lend credence to the exciting prospects that upcoming UHE neutrino telescopes offer for advancing astrophysics and particle physics, potentially leading to major breakthroughs in both.

Victor's thesis is available at the NBI Library for consultation.

Supervisor: Mauricio Bustamante

Opponents: Ralph Engel, Jason Koskinen and Anna Nelles