Theoretical investigations of neutrino and dark matter properties
Date
2016
Authors
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Publisher
University of Delaware
Abstract
There are several questions which couldn't be explained by the Standard Model of particle physics. For example, why the masses of particles of the third family are larger than those of the corresponding particles of the second family, which are larger than those of the first family? (the fermion mass hierarchy). Moreover, the different flavors mix with each other in a way described by mixing angles and complex phase angles. Why the inter-family mixing angles in the leptonic sector are bigger than the ones in the quark sector is still unknown. The problem of explaining the masses and mixing angles of the quarks and leptons is the flavor problem.
Another important unanswered question is that what is dark matter? At this time, almost nothing is known about the dark matter particles, which constitute about 80% of the matter in the universe by mass. No one knows what kinds of particles dark matter is made of, what their masses are, and whether or how they mix or interact. This is the so called dark matter problem. These two questions are the main focus of this thesis. They touch the most fundamental questions in particle physics which involve postulating new physics, i.e. beyond the Standard Model physics.
1. The Flavor Problem: My adviser and I proposed a model in which the mixing angles in both quark and neutrino sectors are controlled by just one single matrix which arises from the mixture of regular Standard Model fermions with extra vector-like fermions in 5 + 5 bar multiplets in SU(5). In the resulting model, all the presently unknown neutrino parameters are predicted, including Dirac neutrino CP phase. Why the inter-family mixing angles in the leptonic sector are larger than the ones in the quark sector is also explained.
The model predicts certain mixing angles within GUT fermion multiplets that are only observable in proton decay. The model also contains certain new scalar particles. If one of these scalars has mass near the weak scale, it will contribute an observable amount to such flavor-changing processes as muon to electron and gamma. The branching ratios for proton decay and flavor-changing lepton decays are calculated. The branching ratios from these processes could give several independent tests of the model.
Moreover, we have proposed a new version of the model in which the inter-family hierarchies among the fermion masses are controlled by another matrix which comes. The combination of this idea with our previous model can give a complete and quite simple account of the entire flavor structure of the quarks and leptons, including mixing angles and mass ratios.
2. The Dark Matter Problem: One of the ideas that has attracted enormous interest in recent years is the idea of asymmetric dark matter. Another is the idea that ordinary matter and dark matter may have been generated together in the early universe by a single mechanism. My adviser and I have proposed a co-generation mechanism that improves on the one proposed in that 1990 paper. This paper proposed that so-called sphaleron processes of the Standard Model could be responsible for co-generating dark matter. We show that sphalerons of a new non-abelian gauge interaction would more easily co-generate dark matter and also lead to definite predictions of the mass of the dark matter particles.