Hunting for new physics signals in the LHC era
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Hunting for new physics signals in the LHC era

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Hunting for new physics signals in the LHC era

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dc.contributor.advisor Pich Zardoya, Antonio
dc.contributor.author Miralles Aznar, Víctor
dc.contributor.other Departament de Fisica Teòrica es_ES
dc.date.accessioned 2022-01-10T10:49:47Z
dc.date.available 2022-01-11T05:45:06Z
dc.date.issued 2021 es_ES
dc.date.submitted 14-01-2022 es_ES
dc.identifier.uri https://hdl.handle.net/10550/81254
dc.description.abstract Currently, the Standard Model of particle physics is able to satisfactorily explain three out to the four fundamental interactions of matter: strong, weak and electromagnetic interactions. However, there are many aspects that this fantastic theory is not able to explain and there must certainly be something beyond it. This thesis aims to find out if there is any indication in the current data of the accelerators that suggests the existence of new physics. We intend, therefore, to determine to which extent some of the new physics models that have been proposed in the literature may be plausible given current data. In this way, we will be able to find constraints on the parameter space of models that extend the scalar sector of the Standard Model with coloured scalars. In addition, we will also be able to constrain the new physics electroweak couplings of the top quark. This thesis is organised in 8 chapters. First of all, in Chapter 1, we present the Standard Model of particle physics, following a (brief) historical perspective. We will see the different facts that led to the final development of this extremely successful theory. Once the Standard Model is well understood, we start to describe in Chapter 2 a possible extension of its scalar sector. The extension that will be presented contains an additional doublet of SU(2)L that is also an octet of SU(3)C. First, we will briefly motivate this model and later explain its most general potential, as well as the different interactions of the new scalars with the Standard Model particles. In Chapter 3 we describe the model-independent framework of Effective Field Theory. We describe the fundamental theorems that lead to this framework and also its extreme relevance for both bottom-up and top-down approaches. In order to do this, we present two examples that will be useful for our research work that will be later described: the Standard Model Effective Field Theory and the Low Energy Effective Field Theory. We finish this chapter with some technical details, which are crucial to predict observables in this framework. Then, in Chapter 4, we present an extremely useful code, HEPfit, that will be used to perform fits in Chapters 6 and 8. In this chapter we will also include a brief discussion about the statistical frameworks that we use in particle physics. Furthermore, we will talk about the Markov Chain Monte Carlo method, which is implemented in this code. The following three Chapters 5, 6 and 7 contain some phenomenological studies of the model presented in Chapter 2. First, in Chapter 5 we find constraints on the masses of the new scalar particles, using data from direct searches at the Large Hadron Collider. After that we perform a global fit of this model, in the CP-conserving limit. As we have already mentioned, in order to do this fit we use the HEPfit code, described in Chapter 4. In this global fit we include all the relevant available observables for this model, including the direct searches of Chapter 5, as well as imposing some theoretical considerations. Finally, in Chapter 7 we present novel contributions of the colour-octet scalars to the electric dipole moment of the neutron. Apart from providing the analytical results, we briefly study the current limits that this observable can generate on its parameter space. The last chapter of the thesis, Chapter 8, contains a detailed study of the top-quark electroweak couplings. In this chapter we employ the model-independent framework that we describe in Chapter 3 to study the effects of possible new-physics particles in the top-quark electroweak couplings. In particular, we present a global fit, performed with HEPfit, within the framework of the Standard Model Effective Field Theory. In order to perform this fit we use the most recent data coming from the Run 2 of the Large Hadron Collider, as well as including some data from LEP and the Tevatron that is still relevant. We finish this chapter studying how these limits would be improved with the data of the High-Luminosity Large Hadron Collider and an electron-positron collider working at different energy ranges. es_ES
dc.format.extent 247 p. es_ES
dc.language.iso en es_ES
dc.subject phenomenology es_ES
dc.subject top-quark es_ES
dc.subject colour-octet scalars es_ES
dc.subject standard model effective field theory es_ES
dc.title Hunting for new physics signals in the LHC era es_ES
dc.type info:eu-repo/semantics/doctoralThesis es_ES
dc.subject.unesco UNESCO::FÍSICA::Física de altas energías::Física teórica altas energías es_ES
dc.embargo.terms 0 days es_ES

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