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Thesis Defense
New Physics with PeV Astrophysical Neutrino Beams
Date: Wednesday, August 17th
Time: 3:00 pm
Place: Chamberlin Hall 4274
Speaker: Ibrahim Safa , Physics PhD Graduate Student
Abstract: Astrophysical neutrinos allow us to access energies and baselines that cannot be reached by human-made accelerators, offering unique probes of new physics phenomena. This thesis aims to address the challenges currently facing searches for Beyond Standard Model (BSM) physics in the high-energy universe using astrophysical neutrinos, particularly in the contexts of flavor measurements and connections with dark matter. The search for new physics with astrophysical neutrinos requires as a prerequisite understanding standard neutrino sources, which remain ambiguous. We begin by performing a multi-wavelength search for astrophysical neutrino sources using nine years of IceCube data. We find hints of neutrino emission from radio-bright Active Galactic Nuclei (AGN), further supporting recent claims that neutrino emission occurs near the core of AGNs. Next we turn our attention to BSM searches. Accurate flavor measurements of the astrophysical flux provide a smoking gun signature to BSM physics. This requires a precise measurement of the tau neutrino fraction. However, tau identification proved a major hurdle in the current generation of observatories. We confront the problem of astrophysical neutrino flavor measurements by first introducing Taurunner, a simulation tool that accurately models the propagation of tau neutrinos including previously neglected effects such as tau lepton energy losses and depolarization in matter. We show that better modeling of tau neutrino propagation improves IceCube transient point-source sensitivities by more than an order of magnitude at EeV energies, and diffuse flux sensitivities by a factor of two. Second, we use this software to model IceCube counterparts to anomalous events reported by the ANITA experiment. After performing an analysis using IceCube data, we show that all Standard Model explanations are ruled out. Looking ahead to the future of flavor measurements, we also present a study that predicts the production of tau neutrinos via the propagation of electron and muon neutrinos in Earth, finding an irreducible but quantifiable background to next-generation tau neutrino observatories. Finally, we attempt to address the field's shared ignorance of the origin of neutrino and dark matter masses by exploring potential connections between the two. Specifically, we present an analysis of dark matter annihilation and decay to neutrinos. We obtain limits from MeV to ZeV masses using more than a dozen neutrino experiments. Notably, using recent data from the SuperKamiokande experiment, we place the first-ever limit on dark matter annihilation that reaches the thermal relic abundance in the neutrino sector, challenging notions that studies with neutrinos cannot be sensitive enough to make strong claims about the nature of dark matter.
Host: Francis Halzen
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