Experimental & Theoretical Aspects of the Electroweak Sector

[摘要] The electroweak sector of the Standard Model (SM) has been extremely successful in predicting and matching observations. The basic form of it was sketched out some fifty years ago with the elucidation of the Higgs mechanism in a non-Abelian Yang-Mills gauge theory, yet the existence of a central player in the story, the (or a) Higgs boson, was confirmed only in 2012. In the intervening years, a great deal of experimental research was done to measure parameters of the model and confirm other predictions. In this sense, it has been an extremely fruitful theory in addition to being robust.But questions regarding the origin of the values of certain parameters in the theory, and especially regarding obvious but unexplained hierarchies between them, beg to be answered. The question of the technical naturalness of the Higgs mass has been one of the most significant motivating factors behind theories of beyond-the-Standard-Model (BSM) physics, though other striking features (for instance, the large discrepancy between quark masses) have also motivated theories (for instance, 2-Higgs-doublet models and models with Yukawa unification). Thus the electroweak sector has also proven fruitful for BSM theorists.The present paper may be divided into two parts: a description and characterization of the electroweak sector as it exists in the Standard Model on the one hand (a SM part), and an exploration of what may lie beyond it on the other (a BSM part).In the SM part, wefirst review the conceptual development of the electroweak model of Glashow, Weinberg, and Salam (touching on Yang-Mills theory and the Higgs mechanism), then present the key phenomenology of the electroweak theory. This leads into a presentation of this author;;s work in studyingnal-state radiation (FSR) uncertainties in a measurement of sin2 W, withW being the weak mixing angle, done by the Compact Muon Solenoid (CMS) group at the Large Hadron Collider (LHC) in 2011. The framework necessary to understand the analysis is laid out in the text but this author played only the small role described in the section on FSR. The full analysis was presented in the papers by N. Tran and the CMS Collaboration, referenced in the text. The BSM part begins with an interlude that includes a review one of the most discussed puzzles of the SM and a discussion of ;;naturalness.;; We then present some of the basics of supersymmetry, including its history, the SUSY algebra, and the MSSM. SUSY is probably the leading contender for an explanation of seemingly ;;unnatural;; parameters. In the next chapter, we present a supersymmetric model in which a new generation of vector-like;; quarks (as opposed to chiral) mixes with the third generation. Such a mixing raises the value of the top Yukawa yt necessary to give a top quark of the observed mass, mt = 173 GeV. Since the one-loop quantum corrections to the Higgs mass scale as yt to the fourth power , even a minor increase in yt can have a large effect. With current experimental bounds, yt may increase by as much as 6%, which implies the top;;s contribution to the Higgs mass increases by up to 26%. The model preserves gauge unification and gives a Higgs mass mh ~ 125.5 GeV without requiring soft supersymmetry-breaking masses above 1 TeV while satisfying all experimental constraints and predicting new quarks around the TeV scale, discoverable at the LHC. We conclude with a summary of the model and remarks on future prospects.

[发布机构] Johns Hopkins University

[效力级别] Supersymmetry

[关键词] Electroweak;Supersymmetry;Beyond the Standard Model;Standard Model;Large Hadron Collider;Higgs boson;Physics