Made available in DSpace on 2014-06-11T19:32:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T19:06:30Z : No. of bitstreams: 1 gomes_ads_dr_ift.pdf: 1153073 bytes, checksum: e0dea491632b14e6b04e8d4834473518 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O mecanismo de Higgs baseado na existência de um bóson escalar fundamental apresenta problemas de hierarquia e naturalidade. Neste trabalho revisitamos os aspectos mais gerais associados a modelos de Technicolor. Em particular, argumentamos que a auto-energia fermiônica deveria apresentar a forma conhecida como Irregular, a qual resolve a maioria dos problemas enfrentados por modelos que seguem esta linha. No último capítulo desta tese elaboramos um modelo, assumindo como solução a forma Irregular para a auto-energia fermiônica, onde as três gerações de férmions adquirem massa via efeitos de quebra dinâmica de simetria. / Abstracts: The Higgs mechanism, based on existence of fundamental scalars bosons suffer from the hierarchy and naturalness problems. In this work we review the main aspects of the Technicolor models. In particular, we aegue that the fermionic self-energy must behave as the Irregular form, that solve most of the Technicolor models problems. In the last Chapter of his thesis we build a model, assuming the Irregular form for the fermionic self-energy, where the three fermionic generations receive mass dynamically.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O presente trabalho tem por finalidade determinar a luminosidade necessária para se impor um limite para exclusão e a signifucância para evidência e descoberta para um bóson de Higgs de mH = 200 GeV no canal qqH → ZZ → 4. Também, apresenta-se uma crítica a qualidade da relação sinal/fundo em eventos de fusão de bósons vetoriais conhecida da literatura atual. / This analysis aims to determine the luminosity required to impose an exclusion limit and significance for evidence and discovery for a Higgs boson of mH = 200 GeV on the channel qqH → ZZ → 4. Also, it presents a critical to the quality of the relation signal/background in vector boson fusion events known form the current literature.

No description available.

This thesis describes searches for a heavy charged Higgs boson decaying into a top and bottom quark pair, and the development of a hardware track trigger with theATLAS experiment. The data for the two searches was collected with the ATLAS detector at the Large Hadron Collider(LHC) with pp collision energies of √s = 8 and 13 TeV, and corresponds to an integrated luminosity of 20.3 and 13.2 fb-1 respectively. The main background for this signal is the production of tt̄ pairs with additional heavy flavor radiation. The searches with a single lepton in the final state found no evidence of a charged Higgs boson, and set 95% CLS upper limits on the production times branching ratio for masses ranging between 200-1000 GeV. The preparation of using the final state with two leptons in future searches is discussed. The design of a hardware track trigger based on pattern matching and linear track fitting was studied for the purpose of reducing the high event rates of the High-Luminosity LHC, which is expected to provide pp collisions with a luminosity about five times the nominal value, in the second half of the 2020’s. A simulation framework was developed to emulate the pattern matching and was used to test its ability to filter hits in high pile-up environments. The results of this simulation, together with simulations of the track fitting and latency, show that such a track trigger is a viable option for the ATLAS experiment in the High Luminosity-LHC era.

This dissertation describes a search for the invisible decays of dark matter particles produced in association with a Z boson, where the latter decays to a charged lepton pair. The dataset for this search includes 13.3 1/fb of collisions recorded in 2015 and 2016 at a centre-of-mass energy of 13 TeV in the ATLAS detector at the Large Hadron Collider in Geneva, Switzerland. The invisible particles manifest themselves as missing transverse momentum, or MET, in the detector, while the charged leptons of interest are electron (e+e-) or muon (mu+mu-) pairs. The models simulated for this study are vector mediated simplified models with Dirac fermionic dark matter particles with couplings g_q = 0.25, g_X = 1 and g_l = 0 . The main background to this analysis, ZZ->llvv, is irreducible, as it shares the same signature as the signal. It is estimated with Monte Carlo simulations including contributions from both qq->ZZ and gg->ZZ production modes. Where possible, other backgrounds are estimated using data-driven techniques and reduced through various selection criteria. The final search is performed by looking for a deviation from the Standard Model background expectation in the MET distribution using two signal regions, e+e- and mu+mu-. This is done using statistical tools to make a likelihood fit and set a 95% confidence level limit as no deviations are found. Limits are placed on the presented model of dark matter for mediator masses up to 400 GeV and for a range of dark matter masses from 1 to ~200 GeV. / Graduate

This thesis describes a series of studies related to searches for new phenomena, beyond the Standard Model of particle physics, in high energy hadron collisions. In such searches, it becomes crucial to identify the Standard Model backgrounds in order to resolve a potential new signal. The thesis presents a method that uses photon events to determine one of such backgrounds, caused by the production of Z boson events. The studies performed to validate the method, both theoretically and experimentally, are presented and the method was shown to be successful as well as to provide reliable results. Theoretically, the method is found to be robust up to a ~10% uncertainty. Experimentally, the method is implemented to estimate the Z(vv) + jets background for the SUSY 0l + E_T^miss + jets search in the ATLAS experiment at the Large Hadron Collider, where this background is one of the most important components for the final sensitivity and is impossible to measure directly. The main experimental results presented are the latest from ATLAS at the time of writing, corresponding to the full dataset of proton-proton collisions delivered by the LHC in 2011 (4.7 fb^-1) at a centre of mass energy of 7 TeV. Given that this method has been mainstream since 2010, brief comparisons to the results from previous analyses that used smaller datasets with the same centre of mass energy are also given, as well as additional cross-checks that support the robustness and validity of the method. The results presented here have contributed to the determination of the world's best limits with respect to SUSY models, which currently exclude equal mass squarks and gluinos below 1.4 TeV.

Über bisherige Aussagen hinausgehend wird ein Weg vorgestellt, der Aussagen über kleinstmögliche Schwarze Löcher gestattet. Es erweist sich, dass es sie (theoretisch) gibt und das sie ein neues stabiles Elementarteilchen (in dieser Arbeit G-Boson genannt) darstellen, das Zusammenhänge zur Dunklen Materie aufzeigt und die Dunkle Energie unabhängig von ihrer in der Makroquantentheorie erforderlichen Existenz notwendig macht, um astronomische Beobachtungen zu erklären. Dadurch ergeben sich logische Abläufe beim Urknall, die diesen in einem etwas anderen Zusammenhang erscheinen lassen als bisher bekannt.:Inhaltsverzeichnis 1. Abstract 2. Einleitung 3. Vorbetrachtung anhand von Planck-Einheiten 4. Die Grenzkraft 5. Grenzkraft und Schwarze Löcher, das G-Boson 6. Eigenschaften des G-Bosons 7. Entstehung der G-Bosonen, die Dunkle Materie und Energie 8. Was bedeutet das für den Urknall? 9. Astronomische Befunde 10. Zusammenfassung

Even though there is a multitude of observational evidence from cosmology and astrophysics, the standard model does not include a suitable dark matter candidate and therefore physics beyond the standard model is necessary. There are hypotheses of what the particle candidate could be coming from theories such as supersymmetry or extra dimensions. The processes producing these particles are understood very well from the theoretical perspective. The problem is that these processes have not been observed in any detectors. Therefore the nature of the dark matter remains unknown. However, it is clear that the dark matter-particle interacts with ordinary matter through gravity and in general, candidates may also interact through the weak force. These candidates are called Weakly Interacting Massive Particles. Therefore, by studying weak processes (weak in the sense that the processes are interactions mediated by a force weaker than the Electro-Magnetic and Quantum-Chromo dynamical-forces, not necessarily the weak force of the standard model) in the large hadron collider it may be possible to pose constraints on the dark matter signatures. One possible process which specifically involves the standard model electroweak interaction, which will be the model for the project, is the emission of scalar dark matter particles from the Z boson,which would result in a final state characterized by a Z boson and missing transverse energy. Simulations of the model and calculations of the cross section are done for different masses, ranging from 20−680 GeV, of the scalar dark matter particle and then compared to a standard model background process. Investigations are made whether or not it would be possible to detect darkmatter signals in the background. With the assumptions made, the results indicate that a signal from dark matter with a mass of around 40−150 GeV could not be rejected up to 5σ.

No description available.

Since the genesis of condensed matter physics, strongly correlated fermionic systems have shown a variety of fascinating properties and remain a vital topic in the field. Such systems arise through electronic interaction, and despite decades of intensive research, no holistic approach to solving this problem has been found. During that time, physicists have compiled a wealth of individual experimental and theoretical results, which together give an invaluable insight into these materials, and, in some instances, can explain correlated phenomena. However, there are several systems that stubbornly refuse to fall completely in line with current theoretical descriptions, among them the high-\( T_c{}\) cuprates and heavy fermion compounds. Although the two material classes have been around for the better part of the last 50 years, large portions of their respective phase diagram are still under intensive debate. Recent experiments in several electron-doped cuprates compounds, e.g. neodymium cerium copper oxide (Nd\(_{2x}\)Ce\(_x\)CuO\(_4\)), reveal a charge ordering about an antiferromagnetic ground state. So far, it has not been conclusively clarified how this intertwining of charge and spin polarization comes about and how it can be reconciled with a rigorous theoretical description. The heavy-fermion semimetals, on the other hand, have enjoyed renewed scientific interest with the discovery of topological Kondo insulators, a new material class offering a unique interface of topology, symmetry breaking, and correlated phenomena. In this context, samarium hexaboride (SmB\(_6\)) has emerged as a prototypical system, which may feature a topological ground state. In this thesis, we present a spin rotational invariant auxiliary particle approach to investigate the propensities of interacting electrons towards forming new states of order. In particular, we study the onset of spin and charge order in high-\( T_c{}\) cuprate systems and Kondo lattices, as well as the interplay of magnetism and topology. To that end, we use a sophisticated mean-field approximation of bosonic auxiliary particles augmented by a stability analysis of the saddle point via Gaussian fluctuations. The latter enables the derivation of dynamic susceptibilities, which describe the response of the system under external fields and offer a direct comparison to experiments. Both the mean-field and fluctuation formalisms require a numerical tool that is capable of extremizing the saddle point equations, on the one hand, and reliably solving a loop integral of the susceptibility-type, on the other. A full, from scratch derivation of the formalism tailored towards a software implementation, is provided and pedagogically reviewed. The auxiliary particle method allows for a rigorous description of incommensurate magnetic order and compares well to other established numerical and analytical techniques. Within our analysis, we employ the two-dimensional one-band Hubbard as well as the periodic Anderson model as minimal Hamiltonians for the high-\( T_c{}\) cuprates and Kondo systems, respectively. For the former, we observe a regime of intertwined charge- and spin-order in the electron-doped regime, which matches recent experimental observations in the cuprate material Nd\(_{2x}\)Ce\(_x\)CuO\(_4\). Furthermore, we localize the emergence of a Kondo regime in the periodic Anderson model and establish the magnetic phase diagram of the two-band model for topological Kondo insulators. The emerging antiferromagnetic ground state can be characterized by its topological properties and shows, for a non-trivial phase, topologically protected hinge modes. / Stark korrelierte Fermionen in einem Festkörper-Kristallgitter weisen eine Vielzahl faszinierender kollektiver Eigenschaften auf und stellen damit eines der konzeptionell reichhaltigsten Themenkomplexe auf dem Gebiet der Physik der kondensierten Materie da. Die dazu nötigen Mechanismen lassen sich auf die elektronische Coulomb-Wechsel-wirkung zurückführen und sind trotz jahrzehntelanger intensiver Forschung bis heute nicht geschlossen gelöst worden. Vielmehr wurden - Stück für Stück - experimentelle und theoretische Einzelergebnisse zusammen getragen, die nicht nur einen tiefen Einblick in diese Materialien geben, sondern in einigen Fällen sogar korrelierte Phänomene erklären können. Allerdings gibt es durchaus Strukturen, die sich hartnäckig weigern, mit den bisherigen theoretischen Beschreibungen vollständig übereinzustimmen, darunter die Kuprat-Hochtemperatursupraleiter und die Schwer-Fermionenverbindungen. Obwohl diese beiden Materialklassen seit etwa 50 Jahren erforscht werden, sind große Teile ihrer jeweiligen Phasendiagramme noch nicht abschließend entschlüsselt. Experimente an mehreren elektronendotierten Kuprat-verbindungen, z. B. Neodym-Cerium-Kupferoxid (Nd\(_{2x}\)Ce\(_x\)CuO\(_4\)), zeigen unter anderem eine Ladungsdichtewelle, die auf einem antiferromagnetischen Grundzustand beruht. Bislang ist nicht abschließend geklärt, wie diese Verschränkung von Ladungs- und Spinpolarisation zustande kommt und wie sie mit einer strengen theoretischen Beschreibung in Einklang zu bringen ist. Schwer-Fermionen Halbmetalle erleben mit der Entdeckung der topologischen Kondo-Isolatoren eine Renaissance und bieten eine einzigartige Schnittstelle zwischen Topologie, Symmetriebrechung und korrelierten Phänomenen. Der wahrscheinlich vielversprechendste Kandidat dieser neuen Materialklasse ist Samariumhexaborid (SmB\(_6\)). In dieser Arbeit nutzen wir einen spinrotationsinvarianten Hilfsteilchenansatz um die Emergenz neuer Ordnungszustände wechselwirkender Elektronen zu untersuchen. Im Besonderen interessiert uns das Zusammenspiel von Spin- und Ladungsdichtewellen in den Hochtemperatur Kupraten und Kondo-systemen, sowie die Interaktion von Magnetismus und Topologie. Dazu verwenden wir eine hoch parametrische Molekular-Feld-Analyse der bosonischen Hilfsteilchen, die anschließend durch eine Stabilitätsanalyse des Sattelpunkts ergänzt wird. Sowohl die Molekular-Feld-Approximation, als auch der Fluktuations-Formalismus erfordern ein numerisches Softwaretool, das in der Lage ist sowohl Sattelpunkt-Gleichungen als auch Loopintegral präzise zu lösen. Wir präsentieren eine pädagogisch aufgearbeitete, von Grund auf entwickelte Herleitung des Formalismus, die auf eine Software-Implementierung zugeschnitten ist. Der Hilfsteilchenansatz erlaubt überdies eine rigorose Beschreibung inkommensurabel magnetischer Ordnungen und reproduziert etablierten numerischen und analytische Ergebnisse in guter Übereinstimmung. Für unsere Analyse verwenden wir sowohl das zweidimensionale Einband-Hubbard- als auch das periodische Anderson-Modell als minimalen Hamitonian für die Hochtemperatur-Kuprate bzw. Kondo-Systeme. Im Falle der Kuprate finden wir eine Phase, die durch eine kombinierte Ladungs- und Spinordnung im elektronendotierten Parameterbereich gekennzeichnet ist und überdies gut mit experimentellen Beobachtungen im Kupratmaterial Nd\(_{2x}\)Ce\(_x\)CuO\(_4\) übereinstimmt. Des Weitern wird das Auftreten des Kondo-Regimes im periodischen Anderson-Modell untersucht und das magnetische Phasendiagramm des Zwei-Band-Hamiltonians eines topologischen Kondo-Isolators kartiert. Der antiferromagnetische Grundzustand kann durch eine topologische Invariante charakterisiert werden und zeigt für eine nicht-triviale Phase eindimensionale topologisch geschützte Kantenmoden.