Leptonic Flavour Symmetries and their Cosmological Dynamics

Abstract

Neutrino oscillations, and the implication of non-zero neutrino masses and mixing,
is one of the most significant particle physics discoveries in
recent times. Flavour symmetries provide a compelling explanation of the pattern of mixing we observe in the lepton sector.
The discovery of neutrino oscillations provides indisputable evidence that neutrinos have non-zero masses and mixing.
Measuring the fine structure of neutrino mixing is one of the foremost challenges in experimental neutrino physics and understanding the origin of the pattern of mixing
is of great interest from a theoretical perspective.

The observed pattern of mixing in the lepton sector could be explained by the presence of a non-Abelian discrete symmetry and in
this doctoral thesis, we study the phenomenological implications of applying a Non-Abelian, discrete flavour symmetry, A, in combination with a generalised
CP symmetry, to the lepton sector. We consider all possible Abelian residual symmetries in the charged lepton () and neutrino () sectors. In the more constrained scenario, the set of
Abelian residual symmetries we study are and . We focus on the mixing
patterns that are compatible with experimental bounds and discuss in detail the testability of these predictions at upcoming accelerator, reactor and neutrinoless double-beta decay experiments. We find the synergy between upcoming oscillation facilities allows for this flavour symmetric approach to be fully tested. In addition, we consider a less constraining set of residual symmetries, and , and find there are many more predictions with more complicated correlations between neutrino parameters.

In complement to the discussion of leptonic flavour symmetries, we present a new mechanism of leptogenesis which proceeds via lepto-bubble nucleation. This mechanism has direct connections with leptonic flavour models and low-energy neutrino parameters. We calculate the lepton asymmetry using the Closed-Time Path formalism and we find the phase transition temperature to be GeV, similar to that of high-scale thermal leptogenesis.