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Due to the mathematical complexity of current musculoskeletal spine models, there is a need for computationally-efficient models of the intervertebral disc (IVD). The aim of this study is to develop a mathematical model that will adequately describe the motion of the IVD under axial cyclic loading and three-dimensional quasi-static loading as well as maintain computational efficiency for use in future musculoskeletal spine models. A viscoelastic standard nonlinear solid (SNS) model is introduced within this study. It was developed to predict the axial response of the human lumbar IVD subjected to low-frequency vibration. Nonlinear axial behavior of the SNS model was simulated by a strain-dependent elastic modulus on the standard linear solid (SLS) model. The SNS model was able to predict the dynamic modulus of the IVD for frequencies of 0.01, 0.1, and 1 Hz. Furthermore, the model was able to quantitatively predict the load relaxation at a frequency of 0.01 Hz. However, model performance was unsatisfactory when predicting load relaxation and hysteresis at higher frequencies (0.1 Hz and 1 Hz). Results suggest that the standard solid model may require strain-dependent elastic and viscous behavior to represent the dynamic response to compressive strain. The SNS model was expanded to a three-dimensional elastic model by adding a matrix of spring elements in parallel with the SNS model. The geometry and orientation of the added elements represent the regional variations in stiffness and physiologic fiber angle. Results suggest that lordotic posture may be advantageous when modeling the intervertebral joint (IVJ) behavior. / Master of Science

In the ATLAS experiment at the Large Hadron Collider (LHC) at CERN, direct searches for the elusive Higgs boson will be conducted, as well as for physics beyond the Standard Model. The charged Higgs boson (H±) is interesting both as a part of the Higgs sector, and as a clear sign of new physics. This thesis focuses on H± searches, with H± production in top-antitop pair events, and in particular the  bW± bH±, H±→τhadν, W±→qq channel. Its potential was investigated  as  part of a larger study of the expected performance of the entire ATLAS experiment. Full simulation of the ATLAS detector and trigger was used, and all dominant systematics considered. It was shown to be the most promising H± discovery channel for mH±<mt. As hadronic τ decays are important for H± searches, their correct identification is critical. Possibilities of improving tau-jet identification in  pile-up and top-antitop pair events were investigated. Redundant or even performance-reducing variables in the default likelihood identification were identified, as were new variables showing discriminatory power. This allows for increased rejection of QCD jets in these environments, and higher robustness of the method. Before any physics studies, a commissioned and well-understood detector is required. The Lorentz angle of the ATLAS Semi-Conductor Tracker (SCT) barrel was measured using 2008 cosmic-ray data. It is an important observable for the performance of several detector aspects. Potential sources of systematics were investigated and evaluated. The Lorentz angle in the SCT barrel was measured as θL = 3.93 ± 0.03(stat) ± 0.10(syst) degrees, agreeing with the model prediction. The Compact Linear Collider (CLIC) is a proposed successor to the LHC. The potential for charged and heavy neutral Higgs bosons at CLIC was investigated, in terms of both discovery and precision measurement of parameters like tanβ or the Higgs masses, up to and beyond 1 TeV, which would be challenging at the LHC

The Standard Model of particle physics successfully describes present collider data. Nevertheless, theoretical and cosmological results call for its extension. A softly broken supersymmetric completion around the TeV scale solves several of the outstanding issues. Supersymmetry requires two Higgs doublets, leading to five physical Higgs states. These include a pair of charged Higgs bosons H±, which are a generic feature of theories with multiple Higgs doublets. Using results from high-energy colliders and flavour physics, constraints are derived on the charged Higgs boson mass and couplings; both for constrained scenarios in the minimal supersymmetric standard model (MSSM) with grand unification, and for general two-Higgs-doublet models. The MSSM results are compared to the projected reach for charged Higgs searches at the Large Hadron Collider (LHC). At the LHC, a light charged Higgs is accessible through top quark decay. Beyond a discovery, it is demonstrated how angular distributions sensitive to top quark spin correlations can be used to determine the structure of the H±tb coupling. The public code 2HDMC, which performs calculations in a general, CP-conserving, two-Higgs-doublet model, is introduced. In parallel to the developments at colliders, the most energetic particles ever recorded are the ultra-high-energy (UHE) cosmic rays. To gain more insight into their origin, new experiments are searching for UHE neutrinos. These searches require detectors of vast volume, which can be achieved by searching for coherent radio pulses arising from the Askaryan effect. The prospects of using a satellite orbiting the Moon to search for neutrino interactions are investigated, and a similar study for an Earth-based radio telescope is presented. In both cases, the method is found competitive for detection of the very highest energy neutrinos considered.

Cette these a pour sujet la recherche de nouvelle physique et l'etude de la production Drell-Yan dans le canal di-electron a l'aide du detecteur CMS au LHC. Certaines theories au dela du Modele Standard (extra dimensions, theories de grande unification) predisent l'existence de particules massives pouvant se desintegrer en une paire d'electrons. La selection des evenements recherches est presentee et etudiee. La strategie d'analyse est introduite et testee. Enfin, l'analyse des premieres donnees a 7 TeV est decrite et les resultats sont commentes. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The Standard Model of particle physics is the framework that describes all known phenomenaand interactions between elementary particles. It has proven to give outstanding results overthe years and was succesfully completed with the discovery of the Brout-Englert-Higgs boson in2012 by the ATLAS and CMS collaborations at CERN. However, several observations escape itsreach: the matter-antimatter asymmetry, the nature of Dark Matter or the quantization of theelectric charge. These are all examples of measured facts not explained by the Standard Modelformalism and that call for an extension to a Beyond the Standard Model (BSM) theory. In thisthesis, we have looked for evidence of new physics using proton-proton collision data producedby CERN’s Large Hadron Collider (LHC) at a center-of-mass energy of 13 TeV. Collected from2016 to 2018 by the CMS detector, it corresponds to an integrated luminosity of 136/fb .Afteran introduction to the theoretical context and the experimental tools, two analyses are presented.The first one is a search for Dark Matter particles recoiling against a jet and leaving the detectorunnoticed. With this ”monojet” analysis, we are able to exclude mediator masses up to 1.8TeV, and masses of Dark Matter particles up to 700 GeV. The second analysis is a search forfractionally charged particles. Using the fact that their stopping power is lower than StandardModel particles, we are able to exclude their existence up to masses of 765 GeV for a charge of2/3 e. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

[pt] O Modelo Padrão de física de partículas é uma das teorias mais bem estabelecidas no campo da física, sendo capaz de fazer previsões verificadas experimentalmente até doze algoritmos significativos. No entanto, o Modelo deixa algumas perguntas sem resposta, o que vem perturbando os físicos por muitos anos. Uma dessas questões é a estrutura hierárquica presente no setor dos férmions, onde matrizes Yukawas possuem autovalores que diferem um do outro por várias ordens de magnitude. Outro aspecto cabível de investigação é relacionado com a matriz CKM, responsável pela mistura entre férmions de sabores distintos. Por que tal matriz é aproximadamente diagonal e por que os ângulos de mistura são tão pequenos? Por que o elétron é muito mais leve que seus primos de outras gerações? A mesma pergunta pode ser feita para os quarks e o Modelo Padrão não seria capaz de responder nenhuma delas. Nesse trabalho, uma explicação proposta vem da utilização de um novo modelo, chamado de Mecanismo Clockwork, que pressupõe a existência de novos férmions pesados, nomeados Clockwork Gears, que são capazes de naturalmente gerar acoplamentos exponencialmente suprimidos a partir de Yukawas de ordem um, após a ocorrência de quebra espontânea de simetria. Além disso, simulações foram feitas com o objetivo de otimizar os parâmetros livres do modelo, assim como confirmar sua eficiência em acomodar os dados experimentais. Por fim, foi feita uma análise de alguns processos, envolvendo correntes neutras que trocam sabor, no regime de teoria efetiva de campo, para poder-se estipular um limite para a escala típica de massa para essas novas partículas. / [en] The Standard Model of particle physics is one of the most well established theories in the field of physics and is able to make predictions correctly measured and verified up to twelve significant figures. However, the theory leaves some unanswered questions that have been bothering physicist for many years. One of those questions is the hierarchical structure of the fermion sector, where Yukawa matrices have eigenvalues that differ from each other by several orders of magnitude. Another aspect concerns the CKM matrix, which dictates the mixing between fermions of distinct flavours: why is this matrix almost diagonal, and why are the mixing angles so small? Why is the electron so much lighter than its cousins from different generations? The same question could be made for the quarks and the Standard Model would not be able to answer neither of these. In this work, an explanation is proposed by employing a novel model, called Clockwork Mechanism, which assumes the existence of new heavy fermion particles, named Clockwork Gears, which are able to naturally generate exponentially suppressed couplings out of order-one Yukawas, after spontaneously symmetry breaking occurs. In addition, simulations were run in order to optimize the free parameters of the model, as well as to confirm its efficiency at fitting with experimental data. Lastly, a few processes involving Flavour Changing Neutral Currents were considered in the effective field theory regime as a means to stipulate a typical mass scale for these new particles.

The Standard Model scalar potential contains a minimum at the Electroweak scale, responsible for the masses of the weak gauge bosons through the Higgs mechanism. However, if the Electroweak minimum is only a local minimum, and there exists a global minimum at a higher energy in the Higgs potential, then in a su ciently old universe we would expect the vacuum expectation value to be at the global minimum. The absence of a global minimum at higher energy is related to the condition that the Higgs self coupling is greater than or equal to zero for all energies. For any model that fails this, we expect new physics to enter before the energy at which the coupling becomes negative. We developed tools to automate the derivation of beta functions for renormalisable gauge theories, and used these to carry out evolution of the renormalisation group equations for the Standard Model and three extensions to the Standard Model | the Standard Model with a fourth generation, the Standard Model with right-handed neutrinos and a Left-Right Symmetric Model. We conclude that of these four models, the Standard Model is the only one in which all the couplings remain perturbative, and in which the Electroweak minimum is a global minimum.

No description available.

No description available.