Doctor of Philosophy (Ph.D.)
Despite the vast success of the Standard Model of particle physics, it is no secret that is also has its shortcomings, thus providing incentive to look beyond the Standard Model for solutions. In this thesis we focus in particular on a model of horizontal flavor symmetry, unification via a universal Landau pole, emergent gravity, and dark matter. First we explain the observed hierarchies in the elementary fermion mass spectrum via a model based on the double tetrahedral group, the smallest discrete subgroup of SU(2), while relaxing previous assumptions of supersymmetry. A sequential symmetry breaking process results in a hierarchy in the Yukawa couplings. Just as the Standard Model raises questions on the origin of the fermion mass spectrum, it similarly raises questions on the origins of its gauge couplings. We have to look beyond the Standard Model for the possibility of a unified description of the electromagnetic, weak and strong forces. As an alternative to conventional unification, we assume the existence of a universal Landau pole in which the gauge couplings blow up at a common scale in the ultraviolet. We consider extensions of the minimal scenario, to see if there are cases that might be probed at a future hadron collider. Next we focus on gravity, the fourth fundamental force that has yet to be embedded in the Standard Model. We consider a model where gravity is an emergent phenomenon in which the graviton appears as a bound state of scalars. We show how this approach can accommodate an arbitrary metric. Lastly we turn to the issue of dark matter, a hypothetical form of matter believed to account for a large portion of the universe but with no place in the Standard Model. We specifically focus on fermionic dark matter that is charged under the simplest non-Abelian dark gauge group. Exotic, vector-like leptons that also transform under the dark gauge group group can mix with standard model leptons and serve as a portal between the dark and visible sectors. We present a framework based on symmetries that allows the mixing between the dark and visible sectors to be non-negligible, while simultaneously suppressing unwanted flavor-changing processes. By extending the particle content and symmetries of the Standard Model, we can solve its various issues. In this thesis we seek to explain the observed hierarchies in the fermion mass spectrum, provide a unified description of the three gauge couplings, generalize a model of emergent gravity, and create a model that gives rise to dark matter via a vector-like fermion portal.
© The Author
Chaurasia, Shikha, "Beyond the Standard Model: Flavor Symmetry, Nonperturbative Unification, Quantum Gravity, and Dark Matter" (2019). Dissertations, Theses, and Masters Projects. Paper 1563898980.