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Title: Phenomenology and naturalness in gauge extensions of the MSSM after the Higgs discovery
Author: Sfondilis, Agamemnon
ISNI:       0000 0004 5992 2595
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 2016
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Supersymmetry remains one of the most favourable candidates for physics beyond the standard model (BSM) due to the solution it provides to the little hierarchy problem as well as the prediction of a Dark matter candidate and other theoretical caveats of the standard model. The minimal supersymmetric standard model despite its success, faces the well known μ problem and the need for large radiative corrections in light of the Higgs discovery which destabilizes the weak scale. Our project addresses this problem in the MSSM and studies the possibility of having a natural theory of singlet extensions of the MSSM with an additional U(1)' gauge group. In a bottom-up approach we have considered a phenomenological version of the gauge extensions of the MSSM (pUMSSM) with generic charges which obey the relations of gauge invariance of the Yukawa terms in the superpotential and perturbativity bounds. Furthermore, we construct a model independent way to impose constraints on the mixing angle from the W mass measurement. We show a strong dependence of the lightest CP-even Higgs boson mass in different models of pUMSSM, on the Higgsino mass μeff and we identify regions of the parameter space in which the Higgs mass is enhanced at tree level by heavy Higgsinos. Furthermore, we analyse the squark sector and find interesting scenarios with heavy third generation squarks with masses directed by large U(1)' D-term contributions. Using the program SARAH and its interface with SPheno, which allow for the calculation of the Higgs mass at the two-loop level in BSM scenarios, we improve the quality and the validity of our results in light of the Higgs discovery. We investigate the role of the gaugino masses M1, M2, M'1 in affecting the fine-tuning at one-loop in the MSSM and in different models of the pUMSSM. A study of the fine tuning measure in MSSM is presented, moreover constraints from collider searches using the program Fastlim are imposed and all points of the parameter scans are being tested. We explore regions of the parameter space in which the natural MSSM scenario is not yet ruled out by currently available searches. We proceed to investigate the fine tuning in scenarios of the pUMSSM with different charge assignments, with light and heavy Z' bosons, and identify interesting regions with low fine tuning. We impose constraints from collider searches on supersymmetric particles using Fastlim and find models which can evade current and future searches at the LHC.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB0460 Astrophysics