Global ETD Search

1	The Little Higgs mechanism and experimental constraints on the Littlest Higgs model Weaver, Benjamin B. 25 November 2013 (has links) We review the important features of Little Higgs models, illuminating the mechanisms that generate a naturally light Higgs field while avoiding excessive fine-tuning. The full spectrum of the Littlest Higgs model is analyzed in light of the recent discovery of the Higgs boson mass. We find viable regions in parameter space that are consistent with the standard model. / text Little Higgs Hierarchy problem Collective symmetry breaking Little Higgs mechanism Simplest Little Higgs Littlest Higgs
2	Phenomenological Studies on Composite Higgs Models El Faham, Hesham January 2018 (has links) Composite Higgs Models (CHMs) are formulated in terms of strongly coupled theories. They often predict fermionic top partners with a mass around the TeV scale. Going beyond minimality enriches the spectrum of the theory with additional hypothetical scalars that significantly change the phenomenology. In this thesis, we explore an SO(6)/SO(5) CHM with an additional pseudo-scalar custodial singlet. The latter has anomalous couplings to the Standard Model vector bosons. We study the phenomenology of the singlet, including bounds from the available ATLAS and CMS searches in the relevant channels with di-boson and fermionic final states. We used HiggsBounds tool to test the model theoretical predictions against the current exclusion limits. The study is performed at the 8 and 13 TeV experiments at the LHC. We present a model parameter space from which the bounds on the (most sensitive) signal cross sections of the hypothetical singlet can be easily extracted. Composite Higgs Hierarchy problem Top partners Custodial symmetry Phenomenology Subatomic Physics Subatomär fysik
3	Phenomenology of the N=3 Lee-Wick Standard Model January 2015 (has links) abstract: With the discovery of the Higgs Boson in 2012, particle physics has decidedly moved beyond the Standard Model into a new epoch. Though the Standard Model particle content is now completely accounted for, there remain many theoretical issues about the structure of the theory in need of resolution. Among these is the hierarchy problem: since the renormalized Higgs mass receives quadratic corrections from a higher cutoff scale, what keeps the Higgs boson light? Many possible solutions to this problem have been advanced, such as supersymmetry, Randall-Sundrum models, or sub-millimeter corrections to gravity. One such solution has been advanced by the Lee-Wick Standard Model. In this theory, higher-derivative operators are added to the Lagrangian for each Standard Model field, which result in propagators that possess two physical poles and fall off more rapidly in the ultraviolet regime. It can be shown by an auxiliary field transformation that the higher-derivative theory is identical to positing a second, manifestly renormalizable theory in which new fields with opposite-sign kinetic and mass terms are found. These so-called Lee-Wick fields have opposite-sign propagators, and famously cancel off the quadratic divergences that plague the renormalized Higgs mass. The states in the Hilbert space corresponding to Lee-Wick particles have negative norm, and implications for causality and unitarity are examined. This dissertation explores a variant of the theory called the N = 3 Lee-Wick Standard Model. The Lagrangian of this theory features a yet-higher derivative operator, which produces a propagator with three physical poles and possesses even better high-energy behavior than the minimal Lee-Wick theory. An analogous auxiliary field transformation takes this higher-derivative theory into a renormalizable theory with states of alternating positive, negative, and positive norm. The phenomenology of this theory is examined in detail, with particular emphasis on the collider signatures of Lee-Wick particles, electroweak precision constraints on the masses that the new particles can take on, and scenarios in early-universe cosmology in which Lee-Wick particles can play a significant role. / Dissertation/Thesis / Doctoral Dissertation Physics 2015 Physics Particle physics Theoretical physics finite temperature hierarchy problem Lee-Wick negative norm phenomenology unitarity
4	Relaxion Physics: a new solution to the hierarchy problem / Física do Relaxion: uma nova solução para o problema da hierarquia Comar, Naim Elias 22 March 2019 (has links) The electroweak hierarchy problem is one of the most important puzzles of particle physics that remains without conclusive answer nowadays. One of the most recent new class of solutions to this problem is presented in this thesis, i.e., the cosmological relaxation of the electroweak scale. In this framework, we postulate the existence of a new particle, the relaxion, which drives the Higgs mass to values much smaller than the cutoff of the theory during inflation. As tools to develop this subject, this work presents a resume of chiral perturbation theory, the strong CP problem, axions and the eta prime particle. Finally, we will describe the most simple model of cosmological relaxation of the electroweak scale and the non-QCD model, where a new strong group SU(N) forms a condensate that interacts with the relaxion. / O problema da hierarquia eletrofraco é um dos enigmas mais importantes da física de partículas que continua sem uma solução conclusiva hoje em dia. Uma nova classe de soluções, dentre as mais recentes, para este problema é apresentado nessa dissertação, i.e., o relaxamento cosmológico da escala eletrofraca. Neste quadro, nós postulamos a existência de uma nova partícula, o relaxion, que conduz a massa do bóson de Higgs para valores muito menores que o cutoff da teoria durante a inflação. Como ferramentas para desenvolver este assunto, este trabalho apresenta um resumo de teoria de perturbação quiral, o problema CP forte, axions e a partícula eta prime. Finalmente, iremos descrever o modelo mais simples de relaxamento cosmológico da escala eletrofraca e o modelo sem-QCD, onde um novo grupo de interação forte SU(N) forma um condensado que interage com o relaxion. Axion Axion Chiral Perturbation Theory Física de Partículas Hierarchy Problem Particle Physics Problema da Hierarquia Relaxion Relaxion Teoria de Perturbação Quiral
5	Hierarquia e naturalidade, uma visão completa do problema e suas possíveis soluções / Hierarchy and naturalness, a complete vision on the problem and its possible solutions Ronqui, Caique Meira 05 February 2018 (has links) Submitted by CAIQUE MEIRA RONQUI null (cmeiraronqui@gmail.com) on 2018-04-05T02:12:52Z No. of bitstreams: 1 mestrado.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) / Approved for entry into archive by Hellen Sayuri Sato null (hellen@ift.unesp.br) on 2018-04-05T16:59:15Z (GMT) No. of bitstreams: 1 ronqui_cm_me_ift.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) / Made available in DSpace on 2018-04-05T16:59:15Z (GMT). No. of bitstreams: 1 ronqui_cm_me_ift.pdf: 19390845 bytes, checksum: a1c62d106479845bd9047a91fbad6b1f (MD5) Previous issue date: 2018-02-05 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / 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. / 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. / 2015/19572-0 Naturalidade Bóson de Higgs Supersimetria Naturalness Problema da hierarquia Divergência quadrática Física além do modelo padrão Running couplings Hierarchy problem Beyond standard model Higgs boson
6	Astrophysical and Collider Signatures of Extra Dimensions Melbéus, Henrik January 2010 (has links) <p>In recent years, there has been a large interest in the subject of extra dimensions in particle physics. In particular, a number of models have been suggested which provide solutions to some of the problems with the current Standard Model of particle physics, and which could be tested in the next generation of high-energy experiments. Among the most important of these models are the large extra dimensions model by Arkani-Hamed, Dimopoulos, and Dvali, the universal extra dimensions model, and models allowing right-handed neutrinos to propagate in the extra dimensions. In this thesis, we study phenomenological aspects of these three models, or simple modifications of them.</p><p> </p><p>The Arkani-Hamed-Dimopoulos-Dvali model attempts to solve the gauge hierarchy problem through a volume suppression of Newton's gravitational constant, lowering the fundamental Planck scale down to the electroweak scale. However, this solution is unsatisfactory in the sense that it introduces a new scale through the radius of the extra dimensions, which is unnaturally large compared to the electroweak scale. It has been suggested that a similar model, with a hyperbolic internal space, could provide a more satisfactory solution to the problem, and we consider the hadron collider phenomenology of such a model.</p><p> </p><p>One of the main features of the universal extra dimensions model is the existence of a potential dark matter candidate, the lightest Kaluza-Klein particle. In the so-called minimal universal extra dimensions model, the identity of this particle is well defined, but in more general models, it could change. We consider the indirect neutrino detection signals for a number of different such dark matter candidates, in a five- as well as a six-dimensional model.</p><p> </p><p>Finally, right-handed neutrinos propagating in extra dimensions could provide an alternative scenario to the seesaw mechanism for generating small masses for the left-handed neutrinos. Since extra-dimensional models are non-renormalizable, the Kaluza-Klein tower is expected to be cut off at some high-energy scale. We study a model where a Majorana neutrino at this cutoff scale is responsible for the generation of the light neutrino masses, while the lower modes of the tower could possibly be observed in the Large Hadron Collider. We investigate the bounds on the model from non-unitarity effects, as well as collider signatures of the model.</p> Extra-dimensional quantum field theories universal extra dimensions Kaluza-Klein dark matter Arkani-Hamed-Dimopoulos-Dvali model hierarchy problem neutrino mass seesaw mechanism Large Hadron Collider phenomenology Elementary particle physics Elementarpartikelfysik
7	Particle Phenomenology of Compact Extra Dimensions Melbéus, Henrik January 2012 (has links) This thesis is an investigation of the subject of extra dimensions in particle physics. In recent years, there has been a large interest in this subject. In particular, a number of models have been suggested that provide solutions to some of the problem with the current Standard Model of particle physics. These models typically give rise to experimental signatures around the TeV energy scale, which means that they could be tested in the next generation of high-energy experiments, such as the LHC. Among the most important of these models are the universal extra dimensions model, the large extra dimensions model by Arkani-Hamed, Dimopolous, and Dvali, and models where right-handed neutrinos propagate in the extra dimensions. In the thesis, we study phenomenological aspects of these models, or simple modifications of them. In particular, we focus on Kaluza–Klein dark matter in universal extra dimensions models, different aspects of neutrino physics in higher dimensions, and collider phenomenology of extra dimensions. In addition, we consider consequences of the enhanced renormalization group running of physical parameters in higher-dimensional models. / QC 20120427 universal extra dimensions hierarchy problem Kaluza– Klein dark matter neutrino mass seesaw mechanism leptonic mixing renormalization group running collider phenomenology Large Hadron Collider
8	Recherche de quarks vectoriels produits par l'échange de gluons lourds dans le cadre de modèles de Higgs composite avec le détecteur ATLAS Dallaire, Frédérick 04 1900 (has links) No description available. LHC ATLAS Higgs composite Problème de hiérarchie Quarks vectoriels VLQ Gluon lourd Production simple 8 TeV Composite Higgs Mass hierarchy problem Vector-like quarks Heavy gluon Single production
9	Astrophysical and Collider Signatures of Extra Dimensions Melbéus, Henrik January 2010 (has links) In recent years, there has been a large interest in the subject of extra dimensions in particle physics. In particular, a number of models have been suggested which provide solutions to some of the problems with the current Standard Model of particle physics, and which could be tested in the next generation of high-energy experiments. Among the most important of these models are the large extra dimensions model by Arkani-Hamed, Dimopoulos, and Dvali, the universal extra dimensions model, and models allowing right-handed neutrinos to propagate in the extra dimensions. In this thesis, we study phenomenological aspects of these three models, or simple modifications of them. The Arkani-Hamed-Dimopoulos-Dvali model attempts to solve the gauge hierarchy problem through a volume suppression of Newton's gravitational constant, lowering the fundamental Planck scale down to the electroweak scale. However, this solution is unsatisfactory in the sense that it introduces a new scale through the radius of the extra dimensions, which is unnaturally large compared to the electroweak scale. It has been suggested that a similar model, with a hyperbolic internal space, could provide a more satisfactory solution to the problem, and we consider the hadron collider phenomenology of such a model. One of the main features of the universal extra dimensions model is the existence of a potential dark matter candidate, the lightest Kaluza-Klein particle. In the so-called minimal universal extra dimensions model, the identity of this particle is well defined, but in more general models, it could change. We consider the indirect neutrino detection signals for a number of different such dark matter candidates, in a five- as well as a six-dimensional model. Finally, right-handed neutrinos propagating in extra dimensions could provide an alternative scenario to the seesaw mechanism for generating small masses for the left-handed neutrinos. Since extra-dimensional models are non-renormalizable, the Kaluza-Klein tower is expected to be cut off at some high-energy scale. We study a model where a Majorana neutrino at this cutoff scale is responsible for the generation of the light neutrino masses, while the lower modes of the tower could possibly be observed in the Large Hadron Collider. We investigate the bounds on the model from non-unitarity effects, as well as collider signatures of the model. / QC 20110324 Extra-dimensional quantum field theories universal extra dimensions Kaluza-Klein dark matter Arkani-Hamed-Dimopoulos-Dvali model hierarchy problem neutrino mass seesaw mechanism Large Hadron Collider phenomenology Subatomic Physics Subatomär fysik
10	Exotic Decays of a Vector-liketop Partner at the LHC Skwarcan-Bidakowski, Alexander January 2019 (has links) An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required. Particle physics Vector-like quarks VLQ Composite Higgs model CHM Top-partner pseudo Nambu-Goldstone boson pNGB NGB ATLAS LHC CMS Significance Recast CheckMate CM MadGraph Pythia Delphes Detector Analysis Hierarchy Problem Exotic Decay QFT Quantum Field Theory fermions bosons Jets photons leptons 13 TeV Missing Transverse Energy momentum hypothetical selection criteria Standard model Signal background event Higgs Mechanism Simulation Confidence limit Other Physics Topics Annan fysik Accelerator Physics and Instrumentation Acceleratorfysik och instrumentering Subatomic Physics Subatomär fysik

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