Study Of Five New Physics Signals In A Two-Higgs-Doublet Model

The Standard Model of particle physics is now the canonical theory in elementary particle physics.Although the Standard Model has succeeded in predicting the scalar Higgs boson and survived almost all the updated experimental tests,there are still some theoretical and experi-mental problems remained to be solved within this model.These include:the fine-tuning issue and the hierarchy problem;the mass hierarchies and flavor mixings among the three-generation fermions;the matter-antimatter asymmetry as well as the origins of dark matter and dark energy observed in the macroscopic universe;the neutrino oscillations,the lepton-flavor universality vi-olation in B-meson physics,as well as the discrepancy between theory and experiment in muonic anomalous magnetic moment,all being observed in microscopic experiments.In order to find an alternative perfect theory beyond the Standard Model that can address all kinds of problems mentioned above,various attempts have been made,and a series of new physics models have been proposed and developed.However,even with abundant new physics models competing in the market,a simple,self-consistent and unified theory has not yet emerged.There is,therefore,definitely a long way to go for the study of new physics theories beyong the Standard Model.In our previous work,we tried to build a two-Higgs-doublet model by adding another Higgs doublet and three right-handed neutrinos to the Standard Model.We aimed to explain the neu-trino mass and mixing via low-scale seesaw mechanism,and to address the lepton-flavor univer-sality violation in B-meson physics and the discrepancy in muonic anomalous magnetic moment with new Yukawa interactions,exploiting gradually a unified new physics model.However,it necessitates a natural symmetry analysis theoretically,so as to reproduce the Yukawa interac-tion structures that are required for a simultaneous explanation of the three problems mentioned above.In this thesis,we have generalized our previous work.Starting from a novel analysis of the flavor symmetry,it is predicted that the Yukawa matrices should follow the Cheng-Sher-type texture.Then,based on such a Yukawa texture,it is found that the neutrino mass and flavor mixing,the lepton-flavor universality violation in B-meson physics,as well as the discrepancy in muonic anomalous magnetic moment can be addressed simultaneously.Furthermore,the lightest heavy neutrino,with a mass being at keV scale,can provide a dark matter candidate.With the freeze-in mechanism,the relic density of dark matter can be given via the decays of the new scalar Higgs bosons.Finally,we discussed the constraints on the model parameter space from B-meson physics,lepton-flavor violating processes,as well as the cosmic X-ray background observation.This thesis is composed of the following chapters:In the first chapter,we will recapitulate the Standard Model of particle physics and the current five new physics signals.In chapter II,we will introduce our new physics model,focusing especially on the Yukawa coupling structures of the model.In chapter ?,based on the Yukawa texture,we will address in turn the neutrino mass and flavor mixing,the lepton-flavor universality violating observables RD(*)and RK(*),the origin of dark matter,as well as the discrepancy in muonic anomalous magnetic moment.Then,in order to further verify the validity of the model,we will discuss other constraints on the model parameter space from B-meson physics,lepton-flavor violating processes,as well as the cosmic X-ray background observation.Finally,we give our conclusions and prospects in the last chapter.