Phenomenology of non-standard neutrino interactions

Resumen

Today neutrino physics is in a privileged position within the fascinating field of particle physics. From the discovery of neutrino oscillations by Super-Kamiokande in 1998, the door to physics beyond the Standard Model (SM in what follows) has been opened. This fact implies that neutrinos have to be massive in opposition to the Standard Model assumption. However, this is not a surprise completely, but it was already hinted from theoretical and experimental observations in the two decades prior to the discovery of the oscillatory phenomenon, as neutrino masses included in unification models or the observed deficit of the atmospheric and solar neutrino fluxes. As a consequence of this new path opened by neutrinos, one could observe processes forbidden in the Standard Model, as decays with lepton flavor violation, neutrinoless double beta decay (or other processes with lepton number violation) or neutrino decays. However, none of the phenomena described previously is foreseen in the SM. Therefore models beyond SM are required to introduce neutrino mass and they may imply new interactions with matter: Non-Standard Interactions (NSI in what follows). In this thesis we study some of these new interactions from a phenomenological point of view. To achieve it, we will use data from several neutrino experiments, performed with different techniques, obtaining extra information on NSI stemming from a combined analysis of them. For this purpose the thesis is organized as follows: - Chapter 1: We begin with a review of the most important characteristics of neutrinos in the Standard Model. Along with them, we will also present other properties of beyond the SM neutrinos, such as neutrino mass, mechanisms to produce it and neutrino oscillations. - Chapter 2: In this chapter we give an introduction to NSI, explaining their appearance and main features. Along with this generic explanation, we will discuss models where NSI appear spontaneously and their influence on neutrino oscillation probabilities and experiments. - Chapter 3: The main goal of this chapter is to show that, although playing a secondary role, NSI still have an influence on the solution of the solar neutrino problem producing an extra region, the so called LMA-Dark solution. Along with this, we combine solar, reactor and accelerator data, in order to get limits on parameters which determine the NSI strength, obtaining better results than in literature. - Chapter 4: In this part of the thesis we get limits on NSI parameters involved in muon-neutrino interactions with quarks. For this purpose, we use the results from a NuTeV reanalysis performed by two collaborations (NNPDF and Bentz et al.), where several uncertainties from QCD have been considered, along with data coming from accelerator and atmospheric neutrino experiments. We find that they are not as strong as previously believed. - Chapter 5: The non-unitarity of the light neutrino mixing matrix is the simplest example of NSI. It is produced when more than three neutrinos are taken into account. In this chapter we describe a formalism which will allow us to work easily with models where more than three neutrinos are considered (as seesaw models), separating the new physics and the standard one. This new formalism is applied to study muon and beta decays, to analyze the oscillation probabilities with more than three neutrinos or to describe (3+1) or (3+3) neutrino schemes. We finish this chapter compiling experimental results on heavy and light neutrino couplings. - Chapter 6: At last, we finish the thesis presenting our conclusions and future prospects.