The phenomenology and cosmological implications of scale invariance
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USyd Access
Type
ThesisThesis type
Doctor of PhilosophyAuthor/s
Liang, Jie YingAbstract
The discovery of the Higgs boson completes the Standard Model (SM) and confirms the mass generation mechanism through spontaneous electroweak symmetry breaking (EWSB). Meanwhile, the SM is only a low-energy effective theory (EFT) that is unable to explain problems such as the origin ...
See moreThe discovery of the Higgs boson completes the Standard Model (SM) and confirms the mass generation mechanism through spontaneous electroweak symmetry breaking (EWSB). Meanwhile, the SM is only a low-energy effective theory (EFT) that is unable to explain problems such as the origin of dark matter and neutrino masses, and thus ‘‘new physics’’ is expected to arise at some scale Λ above the electroweak (EW) scale. In this case a hierarchy problem arises due to the quadratic sensitivity of the quantum corrections of the Higgs mass to the high scale Λ. As an alternative to supersymmetry and technicolour models both of which are still lacking experimental evidence, this thesis considers scale invariance (SI) as a symmetry for solving this hierarchy problem and examined its cosmological implications. Considering the minimal SM as an EFT of a fundamental theory with spontaneously broken SI, a study was performed on the effective theory that exhibits classical SI through the dilaton field. Next, a scale-invariant model was built with dynamical EWSB via top condensation, within the minimal top condensate see-saw framework. In both models, the scalar masses are generated via dimensional transmutation and depend on the (radiatively stable) hierarchy between the EW scale and the large dilaton VEV that defines Λ in this thesis. Cosmological phase transition (PT) is studied within the first aforementioned model, which predicts that the transition of the universe into the chiral symmetry breaking vacuum is of first-order with experimental signals. Finally, a new class of natural inflation models based on hidden SI was introduced, where inflation proceeds without the need for unnatural fine-tuning and the cosmological observables derived in the conformal limit are consistent with current measurements. These models generically predict the existence of the light scalar dilaton, and searches for such particle may reveal a fundamental role of scale symmetry in Nature.
See less
See moreThe discovery of the Higgs boson completes the Standard Model (SM) and confirms the mass generation mechanism through spontaneous electroweak symmetry breaking (EWSB). Meanwhile, the SM is only a low-energy effective theory (EFT) that is unable to explain problems such as the origin of dark matter and neutrino masses, and thus ‘‘new physics’’ is expected to arise at some scale Λ above the electroweak (EW) scale. In this case a hierarchy problem arises due to the quadratic sensitivity of the quantum corrections of the Higgs mass to the high scale Λ. As an alternative to supersymmetry and technicolour models both of which are still lacking experimental evidence, this thesis considers scale invariance (SI) as a symmetry for solving this hierarchy problem and examined its cosmological implications. Considering the minimal SM as an EFT of a fundamental theory with spontaneously broken SI, a study was performed on the effective theory that exhibits classical SI through the dilaton field. Next, a scale-invariant model was built with dynamical EWSB via top condensation, within the minimal top condensate see-saw framework. In both models, the scalar masses are generated via dimensional transmutation and depend on the (radiatively stable) hierarchy between the EW scale and the large dilaton VEV that defines Λ in this thesis. Cosmological phase transition (PT) is studied within the first aforementioned model, which predicts that the transition of the universe into the chiral symmetry breaking vacuum is of first-order with experimental signals. Finally, a new class of natural inflation models based on hidden SI was introduced, where inflation proceeds without the need for unnatural fine-tuning and the cosmological observables derived in the conformal limit are consistent with current measurements. These models generically predict the existence of the light scalar dilaton, and searches for such particle may reveal a fundamental role of scale symmetry in Nature.
See less
Date
2017-12-20Licence
The author retains copyright of this thesis. It may only be used for the purposes of research and study. It must not be used for any other purposes and may not be transmitted or shared with others without prior permission.Faculty/School
Faculty of Science, School of PhysicsAwarding institution
The University of SydneyShare