Phenomenology of neutrino properties, unification, and Higgs couplings beyond the Standard Model

Abstract: The vast majority of experiments in particle physics can be described by the Standard Model of particle physics (SM). However, there are indications for physics beyond it. The only experimentally demonstrated problem of the model is the difficulty to describe neutrino masses and leptonic mixing. There is a plethora of models that try to describe these phenomena and this thesis investigates several possibilities for new models, both full theories and effective frameworks. The values of the parameters in a model are dependent on the energy scale and we say that the parameters run. The exact behavior of the running of the parameters depends on the model, and thus, it provides a signature of the model. For a model defined at high energies, such as a grand unified theory, it is necessary to run the parameters down to the electroweak scale in order to be able to perform a comparison to the known values of observed quantities. In this thesis, we discuss renormalization group running in the context of extra dimensions, where the extra dimensions are perceived as heavy particles in the four-dimensional theory and we provide an upper limit on the cutoff scale. Furthermore, we perform renormalization group running in two versions of a non-supersymmetric $SO(10)$ model and we show that the SM parameters can be accommodated in both versions. In addition, we perform the running for the gauge couplings in a large set of radiative neutrino mass models and conclude that unification is possible in some of them. The Higgs boson, which was discovered at the Large Hadron Collider (LHC) in 2012, provides new possibilities to study physics beyond the SM. The properties of this boson have to be tested with extremely high precision, at the LHC and possibly in future linear colliders, before it could be established whether the particle is truly the SM Higgs boson or not. In this thesis, we perform Bayesian parameter inference and model comparison. For models where the magnitude of the Higgs couplings is varied, we show that the SM is favored in comparison to all other models. Furthermore, the Higgs boson may have couplings to new particles, which are not present in the SM. These could, for example, give rise to Higgs lepton flavor violation. We discuss both types of lepton flavor violating processes in the context of the Zee model, a model where neutrino mass is generated at the one-loop level. We find that these can be sizeable and close to the experimental limits.