L'étude de l'universalité de la saveur des leptons est actuellement un sujet prometteur pour tester la présence de contributions de nouvelle physique dans des processus décrits par le Modèle Standard. Les mesures de désintégrations semitauoniques sont particulièrement intéressantes car de possibles couplages de nouvelle physique au lepton τ pourraient être accrus par rapport aux deux autres leptons du fait de sa masse. Les mesures expérimentales des rapports de branchement des désintégrations B->D*τν et B->Dτν sont présentement en tension avec les prédictions théoriques à la hauteur de 3.78σ. De nouvelles mesures ainsi que l'étude de nouveaux canaux sont ainsi indispensables pour comprendre l'origine de ce désaccord. Le travail présenté dans cette thèse décrit l'utilisation d'une nouvelle technique pour reconstruire le lepton τ via sa désintégration en trois pions et son usage pour mesurer des rapports de rapports de branchements pour deux désintégrations B->D*τν et Λb->Λcτν par rapport aux mêmes désintégrations impliquant des muons. Ces rapports sont respectivement dénommés R(D*) et R(Λc). R(D*) est mesuré en utilisant les 3 fb⁻¹ de collisions proton-proton collectées par le détecteur LHCb pendant le Run1 du LHC à une énergie dans le centre de masse de 7 et 8 TeV via la reconstruction du τ en trois pions. Le résultat obtenu R(D*⁻) = 0.291 ± 0.019(stat) ± 0.026(syst) ± 0.013(ext) est compatible avec la prédiction du Modèle Standard à 1σ près tout en étant cohérent avec les mesures précédemment effectuées. Sa précision permet aussi de conforter le désaccord entre la combinaison des mesures et la prédiction théorique. Ces mêmes données sont aussi analysées dans cette thèse afin d'étudier la désintégration Λb->Λcτν observée pour la première fois avec une significance de 5.7σ. Les incertitudes statistiques et systématiques sont aussi estimées et R(Λc) peut s'écrire R(Λc) = X*(1 ± 0.105(stat) ± 0.162(syst) ± 0.12(ext)) avec la valeur centrale encore masquée à ce jour. / Probing Lepton Flavour Universality has been recently a very promising topic to test for the presence of New Physics contributions in Standard Model processes. Measurements involving semitauonic decays are interesting as potential New Physics couplings to the τ-lepton could be enhanced with respect to the two other leptons due to its mass. Experimental measurements of B->D*τν and B->Dτν branching fractions are currently in tension with theoretical predictions at the 3.78σ level. Both precise measurements and analyses of new channels are thus required to understand the source of this disagreement. The work presented in this thesis describes the use of a new technique to reconstruct τ-lepton using its decay into three pions and its use to measure ratios of branching fractions for two decays B->D*τν and Λb->Λcτν with respect to the same decays involving a muon, these ratios are referred to as R(D*) and R(Λc). Using the 3 fb⁻¹ of proton-proton collisions recorded by the LHCb detector during the LHC Run1 at a centre-of-mass energy of 7 and 8 TeV, R(D*) was measured using the three-pions reconstruction for the τ to be R(D*⁻) = 0.291 ± 0.019(stat) ± 0.026(syst) ± 0.013(ext) This result is compatible with the Standard Model expectation at the 1σ level and is consistent with previous measurements. Its precision is able to slightly enforce the disagreement between the combination of the measurements with the theoretical prediction. The same dataset is also analysed in this thesis to study the Λb->Λcτν decay which is observed for the first time with a significance of 5.7σ. Both statistical and systematic uncertainties were estimated and R(Λc) can then be expressed as R(Λc) = X*(1 ± 0.105(stat) ± 0.162(syst) ± 0.12(ext)) with its central value remaining blind at the moment.

We consider a simple model for invisible neutrino decay as a sub-leading effect in the standard three-flavor neutrino oscillation framework, and use the Cayley–Hamilton formalism to obtain a full set of neutrino oscillation probabilities in matter. These are given as analytical series expansions in the small parameters α ∼ O(λ^2) and s_13 ∼ O(λ), where λ ≡ 0.2 is a “book-keeping parameter” denoting the order of the expansion. We produce explicit formulas for P_eµ, P_eτ , P_µµ, P_µτ , and P_ττ to order O(λ^3), and for P_ee to order O(λ^2), all having first corrections of order O(λ^4). Moreover, we also present vacuum limits of our expressions, as well as discuss the effect of decay on unitarity. We show that all rows in the unitarity table have corrections of order O(λ^2), with the second and third rows having additional corrections of order O(1). In the limit of no decay, unitarity is restored, and we furthermore recover known results for all probabilities. / Vi betraktar en enkel modell för osynligt neutrinosönderfall som en icke-ledande effekt inom det vedertagna ramverket för oscillationer med tre neutrinosmaker och använder Cayley–Hamilton-formalismen för att erhålla en fullständig uppsättning av sannolikheter för neutrinooscillationer i materia. Dessa ges som analytiska serieutvecklingar i de små parametrarna α ∼ O(λ^2) och s_13 ∼ O(λ), där λ ≡ 0.2 är en gemensam “bokföringsparameter” som anger serieutvecklingens ordning. Vi tar fram explicita uttryck för P_eµ, P_eτ , P_µµ, P_µτ och P_ττ till ordning O(λ^3) och för P_ee till ordning O(λ^2), med första korrigeringar för alla sannolikheterna till ordning O(λ^4). Därutöver presenterar vi gränsvärden för våra uttryck i vakuum samt diskuterar sönderfallets inverkan på unitaritet. Vi finner att alla rader i unitaritetstabellen har korrigeringar till ordning O(λ^2) och därtill korrigeringar till ordning O(1) för den andra och tredje raden. I avsaknad av sönderfall återfås unitaritet och vi reproducerar dessutom kända resultatför alla sannolikheter.

We derive the regularised evolution equations for the parton distribution functions that include tensorgluons.

Despite the many successes of the current standard model of cosmology on the largest physical scales, it relies on two phenomenologically motivated constituents, cold dark matter and dark energy, which account for approximately 95% of the energy-matter content of the universe. From a more fundamental point of view, however, the introduction of a dark energy (DE) component is theoretically challenging and extremely fine-tuned, despite the many proposals for its dynamics. On the other hand, the concept of cold dark matter (CDM) also suffers from several issues such as the lack of direct experimental detection, the question of its cosmological abundance and problems related to the formation of structure on small scales. A perhaps more natural solution might be that the gravitational interaction genuinely differs from that of general relativity, which expresses itself as either one or even both of the above dark components. Here we consider different possibilities on how to constrain hypothetical modifications to the gravitational sector, focusing on the subset of tensor-vector-scalar (TeVeS) theory as an alternative to CDM on galactic scales and a particular class of chameleon models which aim at explaining the coincidences of DE. Developing an analytic model for nonspherical lenses, we begin our analysis with testing TeVeS against observations of multiple-image systems. We then approach the role of low-density objects such as cosmic filaments in this framework and discuss potentially observable signatures. Along these lines, we also consider the possibility of massive neutrinos in TeVeS theory and outline a general approach for constraining this hypothesis with the help of cluster lenses. This approach is then demonstrated using the cluster lens A2390 with its remarkable straight arc. Presenting a general framework to explore the nonlinear clustering of density perturbations in coupled scalar field models, we then consider a particular chameleon model and highlight the possibility of measurable effects on intermediate scales, i.e. those relevant for galaxy clusters. Finally, we discuss the prospects of applying similar methods in the context of TeVeS and present an ansatz which allows to cast the linear perturbation equations into a more convenient form.

The cosmic neutrino background (CNB) can be composed of both active and hypothetical sterileneutrinos. At approximately one second after big bang, neutrinos decoupled from radiationand matter at a temperature of approximately one MeV. Neutrinos played an important role inthe origin and evolution of our universe and have been indirectly verified by cosmological dataon the BBN (Big Bang nucleosynthesis) of the Big Bang.It was Steven Weinberg in 1962 that first theorized on the direct detection of relic neutrinos.The signal of the relic neutrino capture on a tritium target can be observed by studying theendpoint of the electrons kinetic energy that are above the endpoint energy of the beta decayspectrum. The PTOLEMY project aims to archive direct detection of the relic neutrinobackground with a large tritium target of 100 gram, MAC-E-Filter, RF-tracking, Time of flighttracking and a cryogenic calorimetry.In this thesis the MAC-E-Filter have been simulated in two filter configurations. In the firstconfiguration, the electron were simulated five times in the filter. Two in the opposite sideof the detector, one in the middle, and two at the detector. In the second configuration theelectrons was simulated in the entrance solenoid at a fixed position of y = -0.19634954 m fromthe center of the filter and in random positions. Both multiple electrons and single electronswere simulated in the second configuration.In the single electron configuration the electron had a starting position of y = -0.19634954 mfrom the center of the filter, and an initial kinetic energy of 18.6 KeV. The first filter configurationsuccessfully accomplished to simulate the electron track, as the electron was reflectedback and forth between the entry and detector solenoid. The electric and magnetic field profilediered at the entry and detector solenoid. The second filter configuration successfully showedthat the electron will reach the end solenoid, when the filter length was 0.5 m. When the filterlength was increased to 0.7 m, then the electron was reflected in the middle of the filter. Thesimulation showed that the electron energy dropped below 1 eV from 18.6 KeV as the electronpropagated through the filter. The magnetic and electric fields decreased exponentially in thedirection of the detector solenoid. The Simulation of multiple electrons showed mixed resultsand would need more modifications in order to come to a final conclusion.

One of the primary targets of current and especially future cosmological observations are light thermal relics of the hot big bang. Within the Standard Model of particle physics, an important thermal relic are cosmic neutrinos, while many interesting extensions of the Standard Model predict new light particles which are even more weakly coupled to ordinary matter and therefore hard to detect in terrestrial experiments. On the other hand, these elusive particles may be produced efficiently in the early universe and their gravitational influence could be detectable in cosmological observables. In this thesis, we describe how measurements of the cosmic microwave background (CMB) and the large-scale structure (LSS) of the universe can shed new light on the properties of neutrinos and on the possible existence of other light relics. These cosmological observations are remarkably sensitive to the amount of radiation in the early universe, partly because free-streaming species such as neutrinos imprint a small phase shift in the baryon acoustic oscillations (BAO) which we study in detail in the CMB and LSS power spectra. Building on this analytic understanding, we provide further evidence for the cosmic neutrino background by independently confirming its free-streaming nature in different, currently available datasets. In particular, we propose and establish a new analysis of the BAO spectrum beyond its use as a standard ruler, resulting in the first measurement of this imprint of neutrinos in the clustering of galaxies. Future cosmological surveys, such as the next generation of CMB experiments (CMB-S4), have the potential to measure the energy density of relativistic species at the sub-percent level and will therefore be capable of probing physics beyond the Standard Model. We demonstrate how this improvement in sensitivity can indeed be achieved and present an observational target which would allow the detection of any extra light particle that has ever been in thermal equilibrium. Interestingly, even the absence of a detection would result in new insights by providing constraints on the couplings to the Standard Model. As an example, we show that existing bounds on additional scalar particles, such as axions, may be surpassed by orders of magnitude.

ATLAS is a multi-purpose detector which has recently started to take data at the LHC at CERN. This thesis describes the tests and calibrations of the central calorimeters of ATLAS and outlines a search for heavy top quark pair resonances.The calorimeter tests were performed before the ATLAS detector was assembled at the LHC, in such a way that particle beams of known energy were targeted at the calorimeter modules. In one of the studies presented here, modules of the hadronic barrel calorimeter, TileCal, were exposed to beams of pions of energies between 3 and 9 GeV. It is shown that muons from pion decays in the beam can be separated from the pions, and that the simulation of the detector correctly describes the muon behaviour. In the second calorimeter study, a scheme for local hadronic calibration is developed and applied to single pion test beam data in a wide range of energies, measured by the combination of the electromagnetic barrel calorimeter and the TileCal hadronic calorimeter. The calibration method is shown to provide a calorimeter linearity within 3%, and also to give a reasonable agreement between simulations and data. The physics analysis of this thesis is the proposed search for heavy top quark resonances, and it is shown that a narrow uncoloured top pair resonance, a Z', could be excluded (or discovered) at 95% CL for cross sections of 4.0±1.6 pb (in the case of M=1.0 TeV/c2) or 2.0±0.3 pb (M=2.0 TeV/c2), including systematical uncertainties in the model, assuming √s = 10 TeV and an integrated luminosity of 200 pb-1. It is also shown that an important systematical uncertainty is the jet energy scale, which further underlines the importance of hadronic calibration.

L'expérience LHCb a été conçue pour étudier la physique des saveurs, dont entre autre la violation de CP, sur le collisioneur proton-proton LHC.La première phase de fonctionnement du LHC a durée de 2011 à 2012, ce qui a permis à LHCb de collecter $3.19~mathrm{fb}^{-1}$ de données à une énergie dans le centre de masse des collisions de $sqrt{s} = 7~TeV$ et $sqrt{s} = 8~TeV$.L'analyse présentée dans cette thèse est basée sur l'ensemble des données collectées par LHCb lors de la première phase de fonctionnement (2011-2012).Le mécanisme de Cabibbo-Kobayashi-Maskawa (CKM) est le mécanisme décrivant la violation de CP dans le cadre du Modèle Standard.Les expériences de la décennie précédente, dédiées à la physique des saveurs, BaBar et Belle, ont permis de démontrer le fonctionnement du mécanisme CKM et de démontrer qu'il est majoritairement Standard.`A présent LHCb a pour objectif de mesurer avec précision les paramètres de ce mécanisme, ce qui constitue des points de références du Modèle Standard, pour en parallèle rechercher de manière indirecte de la Nouvelle Physique en recherchant des déviations à ces points de références du Modèle Standard.Les travaux réalisés lors de cette thèse s'inscrivent dans le cadre du premier axe de recherche: réaliser des mesures de précision des paramètres du mécanisme CKM pour contraindre le Modèle Standard.Dans cette thèse nous réalisons la mesure la plus précise à l'heure actuelle du rapport d'embranchement de la désintégration ${B^0tobar{D}^0K^+K^-}$, la première observation des modes ${B^0_stobar{D}^0K^+K^-}$ et ${B^0_stobar{D}^{*0}phi}$ avec mesure de la polarisation de ce dernier, la confirmation de la mesure du rapport d'embranchement de la désintégration ${B^0_stobar{D}^0phi}$, ainsi que des limites supérieures sur le rapport d'embranchement de la désintégration ${B^0tobar{D}^0phi}$ et sur l'angle de mélange des mésons ${omega - phi}$.L'observation de ces modes ${B^0_{(s)}tobar{D}^0K^+K^-}$ et sous modes ${B^0_{(s)}tobar{D}^{(*)0}phi }$ permet de préparer les futures analyses de Dalitz de ces modes qui contribueront, en les combinant avec les autres méthodes, à améliorer la précision sur la mesure de la phase complexe $gamma$ du mécanisme CKM. / The LHCb experiment has been designed to study flavor physics, notably CP violation, on the LHC proton-proton collider.The first LHC run goes from 2011 to 2012, during what LHCb saved $3.19~mathrm{fb}^{-1}$ of data with a collision centre-of-mass energy at ${sqrt{s} = 7~TeV}$ and ${sqrt{s} = 8~TeV}$.The analysis presented in this thesis is based on a data sample corresponding to the full first run of the LHC (2011-2012).The Cabibbo-Kobayashi-Maskawa (CKM) mechanism describes CP violation in the Standard Model.In the previous decade, two dedicated experiments to flavor physics, BaBar and Belle, proved that the CKM mechanism is at work and dominated by Standard effects.Now LHCb aim is to improve precision on measurements of CKM parameters, in order to serves as the Standard Model reference points, to make in parallel indirect search of New Physics looking for deviations from the Standard Model reference points.Accurate measurements of CKM parameters through different processes provide sensitivity to new physics effects, by testing the global consistency of the Standard Model.This thesis is included inside the first LHCb aim: to improve CKM parameters measurements to constrain the Standard Model.This thesis reports the most precise measurement to date of the branching fraction of ${B^0tobar{D}^0K^+K^-}$ decay, the first observation of the decays ${B^0_stobar{D}^0K^+K^-}$ and ${B^0_stobar{D}^{*0}phi}$ with a polarization measurement for the second one, confirmation of the branching fraction measurement of ${B^0_stobar{D}^0phi}$, and upper limits on branching fraction of ${B^0tobar{D}^0phi}$ decay and on ${omega - phi}$ mixing angle.The observation of ${B^0_{(s)}tobar{D}^0K^+K^-}$ and ${B^0_{(s)}tobar{D}^{(*)0}phi }$ decays prepare the Dalitz analysis for these channels which will be used, combined with other methodes, to improve measurement on the $gamma$ complex-phase of the CKM mechanism.

[pt] O Modelo Padrão é uma das teorias mais bem sucedidas da física de partículas. Com a descoberta do bóson de Higgs, além de ter sido uma demonstração robusta do poder preditivo do Modelo Padrão, foi aberto um novo caminho para a investigação de nova física interagindo por meio do portal de Higgs, incluindo cenários motivados por matéria escura e bariogênese. Investigamos a estabilidade do potencial e os pólos de Landau do Modelo Padrão sob efeito da interação entre o bóson de Higgs e uma partícula escalar. Focamos no regime onde os escalares são gerados primariamente via um off-shell Higgs. Prevemos o espaço de parâmetros disponível para acessar a teoria em diferentes valores de massa do campo escalar. / [en] The Standard Model is one of the most successful theories in particle physics. With the discovery of the Higgs boson, a new pathway has been opened to investigate possible new physics interacting through the Higgs portal, including scenarios motivated by dark matter and baryogenesis. Supposing there is a neutral scalar state in the Standard Model coupled to it only through the Higgs portal, we investigate the potential stability and the Landau poles of the extended Standard Model potential. We focus on the regime in which the scalars are primarily generated via an off-shell Higgs. We predict the available parameter space to probe the theory for different mass values.

Le LHC (Large Hadron Collider) a produit en 2012 des collisions proton proton à une énergie de 8 TeV dans le centre de masse pour les expériences ATLAS et CMS. Ces deux expériences ont été conçues pour découvrir le boson de Higgs et pour rechercher de nouvelles particules prédites par des modèles théoriques. Le boson de Higgs a été découvert le 4 juillet 2012 par les expériences ATLAS et CMS. Cette découverte marque le début d'une nouvelle période de recherche dans le domaine. Avec la confirmation de l'existence du boson de Higgs, les recherches de nouvelle physique liées à ce boson sont devenues prioritaires. Par exemple, on peut chercher dans les données une nouvelle particule massive qui peut se désintégrer dans un boson de Higgs associé à d'autres particules du modèle standard. Une signature attendue est un boson de Higgs avec un quark top, les deux particules les plus lourdes du modèle standard. Le modèle standard prédit une section efficace pour la production du Higgs avec un quark top. Ainsi une mesure de cette section efficace montrant une valeur plus importante prouverait l'existence de physique au-delà du modèle standard. En outre, l'existence de physique au-delà le modèle standard pourrait montrer des résonances qui se désintègrent dans un quark top et un boson de Higgs. Dans la première partie de ce manuscrit, je présente les bases théoriques et expérimentales du modèle standard, ainsi que le dispositif expérimental. Dans le même chapitre théorique je discute une extension du modèle standard dans le cadre d'un modèle effectif englobant ce dernier. De plus, je détaille une étude de faisabilité d'une recherche d'une des nouvelles particules prédites par ce modèle, un quark vectoriel. Dans la deuxième partie, la recherche dans CMS de ce quark vectoriel T_, partenaire du quark top, est décrite. Ce partenaire du top est une nouvelle particule très similaire au quark top du modèle standard, mais beaucoup plus lourde. On considère le cas où ce nouveau quark se désintègre préférentiellement dans un quark top et un boson de Higgs. J'ai fait cette recherche dans le canal hadronique ou le Higgs se désintègre en deux quarks b et le quark top se désintègre en trois quarks, un quark b et deux quarks légers. J'ai reconstruit la masse du T_ à partir de l'identification de tous ses produits de désintégration. Le résultat obtenu est décrit sous forme des limites observées sur la section efficace de production du T_ déduites à partir de cette analyse / During 2012, the Large Hadron Collider (LHC) has delivered proton-proton collisions at 8 TeV center of mass energy to the ATLAS and CMS experiments. These two experiments have been designed to discover the Higgs boson and to search for new particles predicted by several theoretical models, as supersymmetry. The Higgs boson has been discovered by ATLAS and CMS experiments on July, 4th of 2012, starting a new era of discoveries in particle physics domain. With the confirmation of the existence of the Higgs boson, searches for new physics involving this boson are of major interest. In particular, data can be used to look for new massive particles that decay into the Higgs boson accompanied with other particles of the standard model. One expected signature is a Higgs boson produced with a top quark, the two heaviest particles in the standard model. The standard model predicts a cross section of top-Higgs production, then any enhancement of their associated production will be a clear signature of physics beyond the standard model. In addition, the existence of physics beyond the standard model can also be reflected by resonances that decay into a top-quark and a Higgs boson. In the first part of my work I describe the theoretical and experimental foundations of the standard model, as well as the experimental device. In the same theoretical chapter, I also discuss the formulation of an extension of the standard model. In addition, I describe a feasibility study of a search of one of the particles predicted by such model. The second part contains the realization of the search for a top partner, T_, within the CMS experiment. This top partner is a new particle very similar to the standard model top quark, but much heavier, that can decay into a top quark and a Higgs boson. The analysis looks for this particle in the full hadronic final state, where the Higgs boson decays into two b-quarks and the top quark decays into three standard model quarks, a b and two light quarks. In this channel, I reconstruct its mass from the identification of all its decay products. As a result of the analysis, I show the limits on the T_ production cross section from the number of observed events in the specific signature