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Aspects of Radiative Symmetry Breaking in the Standard Model and Beyond

Date

2016-08-25

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Type

Thesis

Degree Level

Doctoral

Abstract

In this thesis, I discuss the conformally symmetric (CS) Standard Model (SM) and the hidden sector extensions to address the hierarchy/ naturalness problem, the origin of electroweak (EW) symmetry breaking (SB), dark matter (DM) candidates and the recent LHC (Large Hadron Collider) diphoton/ diboson anomalies where all the notions are discussed in the introduction. The main body of the thesis (chapter 2-6) where my original works are embedded studies different aspects of the CS hidden sector. The CS SM is the starting point, and further complexity is gradually introduced into the models. In chapter 2, I will show a 125 GeV Higgs mass with a large perturbative Higgs quartic coupling can be naturally realized in the conformal SM. In chapter 3, the minimal extension of the SM: the CS real singlet extension is studied, where the DM decay is protected by the Z_2 symmetry and two SB scenarios (the sequential scenario and dynamical scenario) are developed. In both scenarios, viable DM candidates are obtained. In chapter 4, I discuss the CS complex singlet extension of the SM with a global U(1) symmetry which can be either broken or unbroken and both scenarios are studied to address DM, a second Higgs and the LHC diphoton excess. In the unbroken case, a viable cold DM candidate at 100 GeV is obtained. In the broken case, a renormalization-scale optimization technique is developed to significantly narrow the parameter space and find a 550 GeV second Higgs boson. Upon including the interactions of the complex scalar with an additional vector-like fermion, a 720 GeV mass singlet is found to address the 750 GeV LHC diphoton excess. In chapter 5, the conformal scenario is combined with the asymptotic safety (AS) theory to study an asymptotically safe CS hidden sector. The AS is encoded in UV boundary conditions and renormalization group (RG) equations are used as a bridge to connect UV boundary conditions and EW/ TeV scale physics and furnish a detailed example in the context of a CS leptophobic U(1)' model. In chapter 6, the multi-scale RG method is developed to address the two approximations within the implementation of Gildener Weinberg method: the weak coupling approximation and the simplification of the form of the logarithm. The introduction of an extra renormalization scale allows the mapping of the effective potential onto an RG-equivalent form with a certain symmetric structure, leading to a simplified form of the effective potential.

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Keywords

Conformal Symmetry, Beyond the Standard Model, Hierarchy/ Naturalness Problem, Radiative Symmetry Breaking, Higgs, Dark Matter, Renormalization Group

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Degree

Doctor of Philosophy (Ph.D.)

Department

Physics and Engineering Physics

Program

Physics

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