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# Studies of fine-tuning in extended Higgs models

Zeinstra, Sybrand (2018) Studies of fine-tuning in extended Higgs models. Master's Thesis / Essay, Physics.

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## Abstract

There is great interest in theories that extend the Standard Model. However, these models generally have a larger Higgs sector that can potentially have problems with fine-tuning. We first discuss the SM and its global symmetries. Then we move on to the 2HDM, where we define a general $CP$ transformation, i.e. a $CP$ transformation that can contain a basis transformation. We find that the 2HDM with a $\mathbb{Z}_2$ symmetry is always $CP$ conserving. In order to study fine-tuning we introduce the Dekens and Barbieri-Giudice measures. We find that the 2HDM does not contain fine-tuning. Then we study the $P$-symmetric LR model, which can accommodate Majorana neutrinos. One of the minimum equations of the Higgs potential contains a large ratio due to the hierarchy in vevs in the theory, dubbed the seesaw relation. We consider a special reduced case of the $P$-symmetric LR model that keeps the seesaw relation intact, but this model has problems with naturalness and perturbativity. The Dekens measure, which is sensitive to large ratios in the theory, gives differing results for various choices of dependent parameters, possibly giving a fine-tuning of $\Delta \sim \mathcal{O}(10^{22})$. The BG measure, which looks at fine-tuning in observables finds little fine-tuning. If we put in the constraint that the lowest non-Goldstone boson has a mass close to the SM Higgs mass, we find that in almost all cases $\Delta_{BG}>100$. This fine-tuning arises because the lowest non-Goldstone mass lies close below 2 TeV in most cases.

Item Type: Thesis (Master's Thesis / Essay)
Supervisor:
Supervisor nameSupervisor E mail
Boer, D.D.Boer@rug.nl
Degree programme: Physics
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 07 Aug 2018
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/18255