Zhenyu Han
In this dissertation, a few topics in physics beyond the standard model (SM) of particle physics are studied. These topics can be divided to two parts.
In the first part, electroweak constraints on TeV scale extensions of the SM are discussed. To obtain model-independent results, effective theory approach is adopted. Constraints are computed on effective dimension-6 operators that respect the SM gauge symmetry, as well as CP, lepton and baryon number conservation. Flavor symmetry U(3)5 is also assumed for the operators, which is relaxed to [U(2) × U(1)]5 later. The constraints are given for arbitrary linear combinations of these operators, such that it can be applied to most TeV scale models that have the symmetries assumed above. The results are applied to a variety of little Higgs models as well as a model with the electroweak gauge group extended to SU(2) × SU(2) × U(1). Bounds on the parameter spaces of these models are given and interesting implications are discussed.
The second part of the dissertation is devoted to constructing a realistic model in 5-dimensional spacetime for family unification. A grand unification group SU(5) and a flavor symmetry group SU(2) × U(1) are unified on an S1/ Z2 × Z2 orbifold to a single family group SU(7). The family group is broken to the SM gauge group by both boundary conditions on the orbifold and vevs of some scalar fields. It turns out that the quark and charged-lepton masses and the CKM matrix can be naturally obtained by the interplay of the group structure and the geometry of the extra-dimension.