Yang Bai

The origin of fermion masses and mixings is the least understood aspect of the standard model of particle physics. In this thesis, we try to understand part of it by exploring a framework for the computation of quark and charged lepton mass ratios and CKM mixing angles based on an SU(3) family gauge symmetry. Firstly, we list the field content and the Lagrangian of our model, which has enough global symmetries to protect the first two generations of fermions from developing masses before turning on the family gauge interaction. With the family gauge coupling weak enough and turned on, those mass ratios and mixing angles can be perturbatively calculated, and the results can fit experimental data very well. The neutrino mass matrix is accommodated through a small global symmetry breaking operator. Secondly, by analyzing the symmetry breaking pattern and pseudo Nambu-Goldstone bosons in our model, one U(1) symmetry is found to be unbroken by any of the phenomenologically necessary interactions of the effective field theory, except for QCD anomalies. Thus it can he used as a Peccei-Quinn symmetry to solve the strong CP problem. Then we study the phenomenological consequences of our model such as flavor-changing neutral current processes, which constrain the family gauge symmetry breaking scale to be above 1000 TeV. Finally, in order to address the CP violation in the standard model, we study generally the spontaneous breaking of discrete symmetries in spontaneously broken gauge theories. Depending on the parameters in the effective theory, the discrete symmetry can be broken and the intrinsic violation is naturally of order unity.