A model-building approach to the origin of flavor

Abstract

In this thesis we link the recent anomalies reported in B meson and Higgs boson decays to the smallness of neutrino masses and aspects of the flavor puzzle, including the hierarchy of the Yukawa couplings and the disparate fermion mixings. By formulating various new models we attempt to shed light on the potential common origin of the distinct measurements in the flavor sector. To this end, discrete symmetries are utilized in this work as the governing principle behind all fermion interactions. The first two models based on the S3 and the A4 symmetry, respectively, aim to unify the diverse fermion masses and mixings. Special features separate the frameworks from the flavor models in the literature that often lack testable predictions. While the first model provides interesting flavor-violating signatures in top quark decays, the second one ties the flavor to the grand unification scale in a novel way. In the three following models we focus on the anomalies that hint at lepton flavor and universality violation. We propose that the large flavor violation observed in Higgs boson decays is dictated by the scalar mixing of an enlarged S4-symmetric Higgs sector. By constructing two leptoquark models we show for the first time that leptoquark couplings shaped by a Froggatt-Nielsen mechanism can accommodate the B meson anomalies and simultaneously generate naturally-small neutrino masses. Emphasizing the importance of testability, we demonstrate how these models can be probed by future diphoton resonances, using the recent 750 GeV excess as an example scenario.