Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 241-262). / Microfiche. / xvi, 263 leaves, bound ill. (some col.) 29 cm

Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed March 3, 2009). Graduate School of Arts and Sciences, Dept. of Physics. Includes bibliographical references (p. 116-119).

Thesis (Ph. D.)--Michigan State University. Dept. of Physics and Astronomy, 2008. / Title from PDF t.p. (viewed on Mar. 30, 2009). Includes bibliographical references (p. 137-146). Also issued in print.

Orientador: Rogério Rosenfeld / Coorientador: Alberto Tonero / Banca: Ricardo D'Elia Matheus / Banca: Enrico Bertuzzo / Abstract: The main goal of this dissertation is to show the enhancement of the cross-section for the double Higgs production through pair annihilation by including effective interactions and through the non-perturbative Sommerfeld effect. Bounds to some Wilson coefficients were obtained from such enhancement, this in the scenarios of the future e+ e− -colliders (FCC-ee, ILC, CLIC). In order to achieve this, some computational tools were implemented: FeynRules, FeynArts, FormCalc, and LoopTools. It is also shown the enhancement of the double Higgs production in 2HDM and MSSM, discussing the general framework of these two models. In addition, it is studied the threshold behavior of the cross-section for the double Higgs production when a hidden sector couples to the Higgs boson, yielding resonances below the threshold energy due to non-perturbative effects. We study the Sommerfeld effect in the double Higgs production in the scenario of e+ e− -colliders. The enhancement is discussed as generated from a hidden sector coupled to the Higgs boson. Below and above threshold enhancements are presented. Such analysis is of importance in the ILC project, which will operate up to the threshold energy √s = 250 GeV. The results has been achieved by the use of computational tools like FeynArts, FormCalc, and LoopTools / Resumo: O objetivo principal dessa dissertação é, mostrar o aprimoramento da seção de choque para a produção em dobro dos bósons de Higgs, por meio de aniquilação de pares, incluindo interações efetivas e através do efeito não perturbativo de Sommerfeld. De tais aprimoramentos, os limites para alguns coeficientes de Wilson foram obtidos, isso nos cenários de futuros aceleradores de e+e- (FCC-ee, ILC, CLIC). Para atingir estes resultados, algumas ferramentas computacionais foram implementadas: FeynRules, FeynArts, FormCalc e LoopTools. Também, é mostrado o aprimoramento da produção em dobro de bósons de Higgs no "2HDM" e "MSSM", discutindo o marco geral desses dois modelos. Além disso, foi estudado o comportamento, perto do limite de produção, da seção de choque da produção em dobro dos bósons de Higgs, quando um setor escondido é acoplado ao Higgs, produzindo ressonâncias abaixo da energia limite de produção, devido à efeitos não perturbativos / Mestre

Orientador: Ricardo D'Elia Matheus / Banca: Andre Paniago Lessa / Banca: Sergio Ferraz Novaes / Resumo: Elaboramos uma revisão de como o problema da hierarquia aparece na teoria Eletrofraca, pois entendemos que esse assunto ganhou importância e merece atenção especial. Apesar disso, notamos que muitos conceitos necessários para compreender a origem do problema encontram-se espalhados em diferentes livros e artigos, dificultando o acesso à informação. Por isso, apresentamos neste trabalho esses principais conceitos de maneira consolidada. Evidenciamos como o problema da hierarquia aparece em dois tipos de regularização: cutoff e regularização dimensional. Partimos da Lagrangiana com simetria SU(2)L U(1)Y e promovemos a quebra espontânea dessa simetria. A partir da Lagrangiana espontaneamente quebrada obtivemos as regras de Feynman e calculamos todos os diagramas a 1-loop da auto-energia do bóson de Higgs, que corresponde à primeira correção ao propagador escalar e, a partir do qual, encontramos a primeira correção à massa dessa partícula. A regularização por cutoff gera uma correção à massa do Higgs proporcional ao quadrado do cutoff, deixando explícito o problema da hierarquia, mas para verificar a existência do problema na regularização dimensional calculamos as funções e m definidas na equação de Callan-Symanzik e resolvemos numericamente um sistema de equações diferenciais acopladas para obter o running da massa do Higgs e o running dos acoplamentos das interações eletrofracas. Com isso, foi possível analisar sob quais condições de contorno a massa do Higgs corria para o valor em torno de 125 GeV medido pelos detectores do ATLAS e CMS no LHC. Essas condições estabeleceram uma previsão para a escala de energia na qual esperamos observar física além do Modelo Padrão. Por fim, discutimos como o modelo supersimétrico mais simples resolveria o problema da hierarquia e como a falta de evidência de partículas supersimétricas na faixa de energia procurada pelo LHC afeta essa proposta de solução / Abstract: We develop a review on how the hierarchy problem appears in the Electroweak theory. Nowadays we think that this problem is greater in importance than it was in the past, so it deserves special attention, but we noticed several concepts needed to understand the problem are scattered in different books and papers, which hinders full access to information. Therefore, we intend to present the key subjects in a single document, because we didn't find similar work in previous studies. Additionally, we show how the hierarchy problem appears in two regularization schemes: cutoff and dimensional regularization. Starting from the Lagrangian with SU(2)L U(1)Y symmetry, we perform the spontaneous symmetry breaking. From the spontaneously broken Lagrangian we get the Feynman rules and we calculate all 1-loop diagrams of the Higgs self-energy, which corresponds to the first correction to the scalar propagator and from which we found the first correction to the mass. The cutoff regularization results in a correction proportional to the square of the cutoff. In order to verify the hierarchy problem in dimensional regularization we find the and m functions defined in the Callan-Symanzik equation and numerically solve a system of coupled differential equations to obtain the running Higgs mass and the running electroweak couplings. That allows us to analyze under which boundary conditions the Higgs mass runs to a value around the 125 GeV measured by the ATLAS and CMS detectors at LHC. These conditions establish a prediction for the energy scale where we expect to observe physics beyond the Standard Model. Finally, we discuss how the minimal supersymmetric model solves the hierarchy problem and how the lack of evidence for supersymmetric particles in the range of energy sought by the LHC affects this proposed solution / Mestre

Banca: Marcelo Morael Guzzi / Banca: José Abdalla Helayel / Banca: Arthur K. Antunes Maciel / Banca: Alvaro de Souza Dutra / Banca: Milton Eije Kayama / Texto Sistemático Crítico - Faculdade de Engenharia - Campus de Guaratinguetá - Universidade Estadual Paulista "Júlio de

La découverte d'une particule similaire au boson de Higgs, dernière pièce manquante du Modèle Standard (MS) de la physique des particules élémentaires, est en voie d'être confirmée par les expériences CMS et ATLAS du Large Hadron Collider du CERN. Cependant, il n'est pour le moment pas encore établit que les caractéristiques de la particule observée correspondent aux prédictions du MS. Cela, associé à d'autres observations (Matière Noire,...), motive l'analyse des extensions supersymétriques du MS comme le NMSSM. Nous étudions dans cette thèse la solution au problème de la hiérarchie des échelles d'énergie dans le NMSSM, lié aux divergences quadratiques de la masse du boson de Higgs, ainsi que la phénoménologie du NMSSM avec une brisure de la supersymétrie par interactions de jauge en tenant compte des dernières données du LHC. Enfin, nous détaillons les développements des codes de NMSSMTools effectués au cours de cette thèse~: l'introduction de Chaînes de Markov, le calcul du Fine Tuning, le calcul des cascades de désintégrations des partenaires supersymétriques en particules du MS et l'implémentation du NMSSM général. / The discovery of a particle similar to the Higgs boson predicted by the Standard Model (SM) of particle physics has been confirmed by the experiments CMS and ATLAS of the Large Hadron Collider at the CERN. However, it is not yet clear that the properties of this particle are those predicted by the SM. This, in addition with several other observations (Dark Matter,...), is a motivation for analysing supersymmetric extensions of the SM, as the NMSSM. We study in this thesis the solution of the Hierarchy problem in the NMSSM, linked with the quadratic divergences in the Higgs sector, and also the phenomenology of the NMSSM with gauge mediation supersymmetry breaking in the light of the latest data from the LHC. Finally, we present the developments made in the codes of the package NMSSMTools, featuring Monte Carlo Markov Chain methods, Fine Tuning calculus, the calculus of supersymmetric particle's cascade decays and the implementation of the general NMSSM.

Die vorliegende Arbeit beschreibt die Suche nach der Produktion des Standardmodell Higgs-Bosons in Assoziation mit einem Top-Antitop-Quarkpaar ttH). Der verwendete Datensatz basiert auf einer integrierten Luminositat von 36.1 1/fb, aufgenommen mit dem ATLAS Detektor am Large Hadron Collider in den Jahren 2015 und 2016. Die selektierten Ereignisse enthalten entweder ein oder zwei Leptonen vom Zerfall des Top-Antitop-Quarkpaares. Die Sensitivität der Analyse wurde erhöht, indem die Ereignisse in unterschiedliche Regionen unterteilt wurden, basierend auf der Anzahl der Jets sowie der Wahrscheinlichkeit b-Jets zu enthalten. Methoden basierend auf multivariaten Analysetechniken wurden entwickelt, um ttH Signalereignisse vom Untergrund zu separieren, der von der Produktion von Top-Antitop-Quarkpaaren mit zusätzlichen b-Jets dominiert wird. Alle in der Analyse verwendeten Regionen wurden in einem Profile-Likelihood-Fit kombiniert, um die Vorhersagen des Untergrunds einzuschr{\"a}nken und die systematischen Unsicherheiten zu reduzieren. Ein Überschuss an Ereignissen über dem erwarteten Standardmodell-Untergrund wurde mit einer beobachteten (erwarteten) Signifikanz von 1.4 (1.6) Standardabweichungen gemessen. Die Daten schliessen ttH Signalstärken von mehr als 2.0 mit einem Konfidenzniveau von 95% aus. / This thesis presents the search for the Standard Model Higgs boson produced in association with a pair of top-quarks (ttH). The analysis uses a 36.1 1/fb dataset of proton-proton collisions collected with the ATLAS detector, at the Large Hadron Collider during 2015 and 2016. The selected events contain either one or two leptons from the decay of the top-quark pair. In order to improve the sensitivity of the search, events are split in regions according to the number of jets and how likely these events are to contain b-jets. Methods based on multivariate techniques were developed and applied in the signal-enriched regions to discriminate ttH events against background events being dominated by top pair production with additional b-jets. All analysis regions are combined in a statistical model using a profile likelihood fit to constrain the background predictions and reduce the systematic uncertainties. An excess of events over the expected Standard Model background is found with an observed (expected) significance of 1.4 (1.6) standard deviations. A ttH signal strength larger than 2.0 is excluded at the 95% confidence level.

No description available.

The efficient identification of photons is a crucial aspect in the search for the Higgs boson at ATLAS. With the high luminosity and collision energies provided by the Large Hadron Collider, rejection of backgrounds to photons is of key importance. It is often not feasible to fully simulate background processes that require large numbers of events, due to processing time and disk space constraints. The standard fast simulation program, ATLFAST-I, is able to simulate events ∼1000 times faster than the full simulation program but does not always provide enough detailed information to make accurate background estimates. To bridge the gap, a set of photon reconstruction efficiency parameterisations, for converted and unconverted photons, have been derived from full simulation events and subsequently applied to ATLFAST-I photons. Photon reconstruction efficiencies for isolated photons from fully simulated and ATLFAST-I, plus parameterisations, events are seen to agree within statistical error. A study into a newly proposed Two Higgs Doublet Model channel, gg → H → hh → γγγγ, where the light Higgs (h) boson is fermiophobic, has been investigated. The channel is of particular interest as it exploits the large production cross-section of a heavy Higgs (H) boson via gluon-fusion at the LHC in conjunction with the enhanced branching ratio of a light fermiophobic Higgs (h) boson to a pair of photons. This channel is characterised by a distinct signature of four high pT photons in the final state. Samples of signal events have been generated across the (mh,mH) parameter space along with the dominant backgrounds. An event selection has been developed with the search performed at generator-level. In addition, the search was also performed with simulated ATLFAST-I events utilising the above photon reconstruction efficiency parameterisations. For both analyses, the expected upper limit on the cross-section at 95% confidence level is determined and exclusion regions of the (mh,mH) parameter space are defined for integrated luminosities of 1 f b−1 and 10 f b−1 in seven fermiophobic model benchmarks.