Although the Standard Model (SM) of particle physics describes observations well, there are several shortcomings of it. The most crucial of these are that the SM cannot explain the origin of neutrino masses and the existence of dark matter. Furthermore, there are several aspects of it that are seemingly ad hoc, such as the choice of gauge group and the cancellation of gauge anomalies. These shortcomings point to a theory beyond the SM. Although there are many proposed models for physics beyond the SM, in this thesis, we focus on grand unified theories based on the SO(10) gauge group. It predicts that the three gauge groups in the SM unify at a higher energy into one, which contains the SM as a subgroup. We focus on the Yukawa sector of these models and investigate the extent to which the observables such as fermion masses and mixing parameters can be accommodated into different models based on the SO(10) gauge group. Neutrino masses and leptonic mixing parameters are particularly interesting, since SO(10) models naturally embed the seesaw mechanism. The difference in energy scale between the electroweak scale and the scale of unification spans around 14 orders of magnitude. Therefore, one must relate the parameters of the SO(10) model to those of the SM through renormalization group equations. We investigate this for several different models by performing fits of SO(10) models to fermion masses and mixing parameters, taking into account thresholds at which heavy right-handed neutrinos are integrated out of the theory. Although the results are in general dependent on the particular model under consideration, there are some general results that appear to hold true. The observ- ables of the Yukawa sector can in general be accommodated into SO(10) models only if the neutrino masses are normally ordered and that inverted ordering is strongly disfavored. We find that the observable that provides the most tension in the fits is the leptonic mixing angle θ2l3, whose value is consistently favored to be lower in the fits than the actual value. Furthermore, we find that numerical fits to the data favor type-I seesaw over type-II seesaw for the generation of neutrino masses. / <p>Examinator: Professor Mark Pearce, Fysik, KTH</p>

[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.

Dans la première partie de cette thèse, je présenterai le 5D MSSM qui est un modèle super symétrique avec une dimension supplémentaire. (Five Dimensional Minimal Supersymmetric Standard Model). Apres compactification sur l'orbifold S1/Z2, le calcul des équations du groupe de renormalisation (RGE) à une boucle montre un changement dans l'évolution des paramètres phénoménologiques. Dès que l'énergie E = 1/R est atteinte, les états de Kaluza- Klein interviennent et donnent des contributions importantes. Plusieurs possibilités pour les champs de matière sont discutés : ils peuvent se propager dans le "bulk" ou ils sont localisés sur la "brane". Je présenterai d'une part l'évolution des équations de Yukawa dans le secteur des quarks ainsi que les paramètres de la matrice CKM, d'autre part, les effets de ce modèle sur le secteur des neutrinos notamment les masses, les angles de mélange, les phases de Majorana et de Dirac. Dans la deuxième partie, je parlerai du modèle AMSB et ses extensions (MM-AMSB et HCAMSB). Ces modèles sont des scenarios de brisure assez bien motivés en super symétrie. En calculant des observables issues de la physique des particules puis en imposant des contraintes de cosmologie standard et alternative sur ces scénarios, j'ai déterminé les régions qui respectent les contraintes de la matière noire et les limites de la physique des saveurs. Je reprendrai ensuite l'analyse de ces modèles en utilisant de nouvelles limites pour les observables. La nouvelle analyse est faite en ajoutant les mesures récentes sur la masse du Higgs et les rapports de branchement pour plusieurs canaux de désintégrations / In the first part of this thesis, we review the Universal Extra-Dimensional Model compactified on a S1/Z2 orbifold, and the renormalisation group evolution of quark and lepton masses, mixing angles and phases both in the UED extension of the Standard Model and of the Minimal Supersymmetric Standard Model (the five-dimensional MSSM). We consider two typical scenarios: all matter fields propagating in the bulk, and matter fields constrained on the brane. The two possibilities give rise to quite different behaviours. For the quark sector we study the Yukawa couplings and various flavor observables and for the neutrino sector, we study the evolution of neutrino masses, mixing angles and phases. The analysis is performed in the two cases for different values of tan β and different radii of compactification. The resulting renormalization group evolution equations in these scenarios are compared with the existing results in the literature, together with their implications. In the second part, we present a simulation study about anomaly mediated supersymmetry breaking and its extensions. Anomaly mediation is a popular and well motivated supersymmetry breaking scenario. Different possible detailed realisations of this set-up are studied and actively searched for at colliders. Apart from limits coming from flavour, low energy physics and direct collider searches, these models are usually constrained by the requirement of reproducing the observations on dark matter density in the universe. We reanalyse these bounds and in particular we focus on the dark matter bounds both considering the standard cosmological model and alternative cosmological scenarios. We briefly discuss the implications for phenomenology and in particular at the Large Hadron Collider. After that we update our analysis by using new limits from observables and adding recent Higgs boson measurements for the mass and signal strengths in different decay channels