PhD defense by Tetiana Kozynets

Title: Atmospheric neutrino oscillations in IceCube-DeepCore within and beyond the unitary framework

Abstract:

A key unresolved question in the Standard Model of particle physics is the origin of neutrino masses. A class of models explain the very small yet non-vanishing neutrino masses through the existence of heavy and non-weakly interacting neutrino states, leading to a breach in unitarity of the three-flavor mixing framework. Motivated by such models, this thesis focuses on tests of unitarity of the neutrino mixing matrix using neutrino oscillation data.

In the first part of this thesis, we combine the atmospheric neutrino data from IceCube-DeepCore with the reactor neutrino data from the Daya Bay and KamLAND experiments to constrain the individual elements of the mixing matrix and derive the non-unitarity metrics. Further, we show how these constraints would improve with the next-generation atmospheric and reactor neutrino experiments, including the IceCube-Upgrade and JUNO, respectively.

Finally, we present the contributions towards an improved event selection in IceCube-DeepCore, incorporating nine years of data to probe unitarity in the tau sector with greater precision.