Le Modèle Standard (MS) de la physique des particules s’est imposé comme étant la description la plus précise des interactions fondamentales entre les particules élémentaires. La découverte d’un boson de Higgs, avec une masse de 125 GeV, en Juillet 2012 au Large Hadron Collider (LHC), en a marqué sa confirmation définitive. Cependant, de nombreux problèmes observationnels et théoriques sont au coeur du MS, la plupart liés au secteur de Higgs. Etant une particule scalaire, le boson de Higgs souffre de très grandes corrections radiatives, ce qui déstabilise l’échelle électro-faible et mène au problème de hiérarchie. L’un des buts principaux du LHC est d’explorer précisément le secteur de Higgs, afin de caractériser le mécanisme à l’origine de la brisure de la symétrie électro- faible et de tester de possibles solutions au problème de hiérarchie. Le secteur de Higgs est également responsable de la génération des masses des fermions dans le MS, par le biais des couplages de Yukawa. Ces couplages sont extrêmement non génériques et cela mène aux problèmes de la saveur au delà du MS.La première partie de cette thèse se concentre sur la caractérisation précise du secteur de Higgs. En particulier, le code public Lilith est présenté, il permet de dériver des contraintes sur des scénarios de nouvelle physique à l’aide des mesures des propriétés du boson de Higgs en collisionneurs. Une analyse des couplages du boson de Higgs dans le contexte de plusieurs scénarios est ensuite effectuée. Dans la seconde partie, la phénoménologie des modèles à deux doublets de Higgs est étudiée à la lumière des résultats de la première phase du LHC. La limite d’alignement, ainsi que la possible présence de bosons de Higgs légers, sont étudiées en détail. Finalement, dans la dernière partie de cette thèse, l’hypothèse de Violation Minimale de la Saveur est introduite comme une solution potentielle aux problèmes de la saveur au delà du MS. Appliquée au Modèle Standard Supersymétrique Minimal, l’évolution des couplages baryoniques violant la parité R sous le groupe de renormalisation est analysée en détail. / The Standard Model (SM) of particle physics stands as the most successful description of the fundamental interactions between elementary particles. The discovery of a Higgs boson, at a mass of 125 GeV, in July 2012 at the Large Hadron Collider (LHC), marked its ultimate confirmation. However, various observational and theoretical problems lie in the heart of the SM, with the majority of them linked to the Higgs sector. Being a scalar, the Higgs boson is subject to very large radiative corrections and this ultimately leads to the electroweak hierarchy problem. One of the main goals of the LHC program is to precisely probe the Higgs sector, in order to characterize the mechanism at the origin of the breaking of the electroweak symmetry and test possible solutions to the hierarchy problem. The Higgs sector is also responsible for the generation of the fermion masses, as it induces the Yukawa couplings. The SM flavor sector is highly hierarchical and this leads to flavor puzzles in theories beyond the SM.The first part of this thesis is dedicated to the precise characterization of the Higgs sector. In particular, the public tool Lilith is presented, which allows to derive constraints on new physics models based on the Higgs measurements at colliders. It is then used to perform global fits of the Higgs couplings in the context of various scenarios. In the second part, the phenomenology of two-Higgs-doublet models is studied in the light of the results from the first run of the LHC. The so-called alignment limit is explored in detail, as well as the possible presence of light scalar states. Finally, in the last part of this thesis, the Minimal Flavor Violation hypothesis is introduced as a possible solution to the flavor puzzles beyond the SM. Enforcing it in the Minimal Supersymmetric Standard Model, the renormalisation group evolution of the baryonic R-parity violating couplings is then studied in detail.

Le Modèle Standard Supersymétrique Minimal (MSSM), le plus étudié des modèles de Nouvelle Physique, contient un candidat à la matière noire : le neutralino. Un des mécanismes qui permet de réduire la densité relique de neutralino jusqu'à l'intervalle expérimental de WMAP et de Planck est la coannihilation entre le neutralino et le stop. Dans cette thèse nous étudions deux aspects différents liés à la prédiction de la densité relique dans la région de coannihilation neutralino-stop, ainsi qu'au calcul des sections efficaces d'annihilation et de coannihilation correspondantes. Nous présentons tout d'abord la matière noire en tant que WIMP ainsi que le Modèle Standard de la Physique des Particules, puis nous abordons le MSSM ainsi la phénoménologie de la densité relique de neutralino. Nous étudions ensuite la phénoménologie de la violation de saveur non minimale dans le secteur des squarks dans le contexte de la densité relique de neutralino. Nous considérons des termes violant la saveur dans le secteur des squarks up et down de chiralité droite et de troisième génération et montrons qu'ils peuvent avoir un impact important sur les sections efficaces d'annihilation et de coannihilation du neutralino, et en conséquence sur la densité relique. Finalement, nous nous intéressons à la possibilité d'améliorer la précision avec laquelle la densité relique est prédite, en calculant les sections efficaces d'annihilation et de coannihilation à l'ordre supérieur dans la théorie des perturbation. En se basant sur des travaux antérieurs qui ont montré que l'impact des corrections SUSY-QCD à une boucle pour l'annihilation de neutralino était supérieur à l'incertitude expérimentale, nous avons calculé de telles corrections dans le cas de la coannihilaiton neutralino-stop en bosons de jauge électrofaibles et bosons de Higgs. / The Minimal Supersymmetric Standard Model (MSSM), the most famous model of Physics beyond the Standard Model, provides a good dark matter candidate: the neutralino. One of the mechanisms which can reduce the predicted relic density of neutralino to the experimental range of WMAP and Planck is the coannihilation between the neutralino and the stop. In this thesis, we study two different aspects related to the prediction of the relic density in the neutralino-stop coannihilation region and the calculation of the corresponding annihilation and coannihilation cross sections. We first make short reviews of WIMP dark matter and the Standard Model of particle Physics, introduce the MSSM and discuss the phenomenology of neutralino relic density. We then study the phenomenology of Non Minimal Flavor Violation in the squark sector in the context of neutralino relic density. We consider flavor violating terms in the sectors of right handed third generation up and down squarks and show that they can have an important impact on the thermally averaged (co)annihilation cross section of the neutralino, and therefore on its relic density. Finally, we focus on the issue of improving the precision with which the relic density is calculated, by computing (co)annihilation cross sections at Next-to-Leading Order. Following earlier work in the calculation of one-loop SUSY-QCD corrections to the annihilation of neutralinos, which have shown that the impact of such corrections was larger than the experimental uncertainty, we have calculated similar corrections for the neutralino-stop coannihilation into electroweak gauge and Higgs bosons.

The discovery of the Higgs boson by the LHC provided the last piece of the puzzle neces- sary for the Standard Model (SM) to be a successful theory of electroweak scale physics. However there exist various phenomenological reasons which serve as pointer towards the existence of physics beyond the Standard Model. For example the explanation for the smallness of the neutrino mass, baryon asymmetry of the universe, the presence of dark matter and dark energy etc. are not within purview of the Standard Model. Con- ceptual issues like the gauge hierarchy problem, weakness of gravity provide some of the theoretical motivation to pursue theories beyond the SM. We consider scenarios with warped extra-dimensions (Randall-Sundrum (RS) Model ) as our preferred candidate to answer some of the questions raised above. RS model gives an elegant geometric solution to address the hierarchy between the two fundamental scales of nature i.e. Planck scale and electroweak scale. In addition to this, the geometry of RS serves as a useful setup wherein the fermion mass hierarchy problem can also be solved. The goal of this thesis is to investigate whether RS model can be an acceptable theory of avour while at the same time serving as a solution to the hierarchy problem. In Chapter[1] we begin with a brief introduction of the SM, highlighting issues which pro- vides the necessary motivation for constructing new physics models. Various candidates of Beyond Standard Model (BSM) physics are introduced and a few preliminaries es- sential to understand frameworks with additional spatial-dimensions ( at and warped) is provided. In Chapter[2] we specialize to the case of warped extra-dimensions and motivate the need to have the SM elds in the bulk. Mathematical details related to the analysis of various spin elds (0; 12; 1 and 2) in a warped background necessary to understand relevant phenomenology is provided. The lack of knowledge of Dirac or Majorana nature of the neutrino leads to a wide variety of possibilities as far as neutrino mass generation is concerned. In Chapter[3] we focus on the leptonic sector where three cases of neutrino mass generation are consid- ered: a)Planck Scale lepton number violation (LLHH case) b) Dirac neutrinos c) Bulk Majorana mass terms. We then study the implications of each case on the charged lepton mass tting. The case with Planck scale lepton number violation in normal RS scenario requires large and negative values for the bulk mass parameters for the charged singlets cE. Dirac neutrinos and the case with Bulk Majorana mass terms give good t to data. For completeness, the ts for the hadronic sector is provided in the appendix. In Chapter[4] avour violation for each of three cases introduced in Chapter[3] is studied. For the case with Planck scale lepton number violation, the non-perturbative Yukawa coupling between the SM singlets and the KK states render the higher order diagrams incalculable. Lepton avour violation (LFV) is particularly large for the Dirac case and the bulk Majorana case for low Kaluza-Klein(KK) mass scales. We then invoke the ansatz of Minimal Flavour violation to suppress LFV with low lying KK scales and examples of avour group is provided for both cases. In Chapter[5] we present an example with a type II two Higgs doublet model applied to the LLHH case. The setup o ers a solution where LLHH scenario can be consistently realized in RS model, where the masses and mixing angles in the leptonic sector can bet with O(1) choice of bulk parameters. Assumption of global lepton number conservation (like in Dirac neutrinos) could lead to problems in theories of quantum gravity where it does not hold. This leads us to the question whether Dirac neutrinos can be naturally realized in nature. In Chapter[6] we consider the special case of bulk Majorana mass encountered in Chapter[3] where the bulk Dirac mass terms for the right handed neutrino is set to zero. We nd that this leads to a case where the e ective zero mode neutrino mass is of Dirac type with negligible e ects from the tower of Majorana states. In Chapter[7] we consider RS at the GUT scale which no longer serves as a solution to the hierarchy problem. SUSY is introduced in the bulk and the low energy SUSY serves as a solution to the hierarchy problem. Such models serve as a useful alternative to SUSY models with family symmetries (e.g. Froggatt-Nielsen Model). However the solutions to the Yukawa hierarchy problem are constrained due to anomaly cancellation conditions. In Chapter[8] supersymmetry breaking due to radion mediation in addition to brane localized sources is considered and detailed analysis of the running of soft masses and the low energy avour observables is considered for both cases separately. In Chapter[9] we conclude and present future directions.