Phenomenology and numerical analysis of the complex singlet extension of the Standard Model

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Title: Phenomenology and numerical analysis of the complex singlet extension of the Standard Model
Author: Stendahl, Alex
Contributor: University of Helsinki, Faculty of Science
Publisher: Helsingin yliopisto
Date: 2020
Language: eng
Thesis level: master's thesis
Degree program: Alkeishiukkasfysiikan ja astrofysikaalisten tieteiden maisteriohjelma
Master's Programme in Particle physics and Astrophysical Sciences
Magisterprogrammet i elementarpartikelfysik och astrofysikaliska vetenskaper
Specialisation: Alkeishiukkasfysiikka ja kosmologia
Particle Physics and Cosmology
Elementarpartikelfysik och kosmologi
Discipline: none
Abstract: The Standard model of particle physics has been very successful in describing particles and their interactions. In 2012 the last missing piece, the Higgs boson, was discovered at the Large Hadron Collider. However even for all its success the Standard model fails to explain some phenomena of nature. Two of these unexplained phenomena are dark matter and the metastability of the electroweak vacuum. In this thesis we study one of the simplest extensions of the Standard model; the complex singlet scalar extension. In this framework the CP-even component of the singlet mixes with the Standard model like Higgs boson through the portal operator to form new mass eigenstates. The CP-odd component is a pseudo-Goldstone boson which could be a viable dark matter candidate. We analyse parameter space of the model with respect to constraints from particle physics experiments and cosmological observations. The time evolution of dark matter number density is derived to study the process of dark matter freeze-out. The relic density of the Dark Matter candidate is then calculated with the micrOmegas tool. These calculations are then compared to the measured values of dark matter relic density. Moreover, the electroweak vacuum can be stabilised due the contribution of the singlet scalar to the Standard Model Higgs potential. We derive the β-functions of the couplings in order to study the renormalisation group evolution of the parameters of the model. With the contribution of the portal coupling to the β-function of the Higgs coupling we are able to stabilise the electroweak vacuum up to the Planck scale. The two-loop β-functions are calculated using the SARAH tool.
Subject: Standard model
Singlet extension
dark matter
electroweak vacuum

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