Neutrino physics from cosmological observables and oscillation experiments

Laburpena

This thesis is focused on neutrino physics. In particular, it is centred on the study of flavour oscillations and the role of relic neutrinos in some cosmological scenarios. Neutrinos are among the most interesting known elementary particles. They exhibit interesting behaviours, such as their oscillations, and constitute one of the links among different areas in physics. We are going to exploit their relation with cosmology, with special emphasis on the early Universe. In the first part of the thesis wepresent a global fit of all relevant neutrino oscillation experiments, where we show the astonishing capability of joint analyses through the particular determination at more than three sigmas in favour of a normal ordering of neutrino masses. The second part of the work is devoted to the decoupling process of relic neutrinos, with special care devoted to the role of flavour oscillations. We have relaxed previous approximations in this regard and we have improved the determination of the effective number of neutrinos, an important cosmological parameter that describes the contribution of radiation. Afterwards, we study several non-standard cosmological scenarios where neutrinos are relevant. The first one involves a very low-reheating temperature, where we set the best lower bounds up to date on this parameter. In a second study, we investigate the statistical properties of neutrinos from cosmological measurements. Then we leave the early Universe behind and, still dealing with relic neutrinos, we move towards present times to study their clustering under the gravitational potential of the Milky Way. With this computation, we have calculated the local overdensity of these relics, an important value for future experiments aiming at their detection. Finally, in the last part of the thesis we change the type of neutrinos and investigate those that can be detected with the largest energies. In particular, we have calculated the impact that a hypothetical interaction between neutrinos and dark matter particles, with the major constraint that this interaction must be non-universal, can have on the pattern of flavour oscillations at such extreme energies. We made the calculations taking into account the fact that the dark matter is not homogeneously distributed in our galaxy, what can lead to MSW-like effects. All in all, we have contributed to the knowledge of the role that relic neutrinos play in the Universe, in particular at its earlier stages, and we have investigated flavour oscillations, both in standard and non-standard scenarios. Hopefully this work will be useful for the understanding of some of the currently open problems in particle physics, astrophysics and cosmology.