Date and time: December 4th, 2017 at 11:00 CET

Speaker: Josu Hernandez

Title: The Quest for the Origin of Neutrino Masses

Abstract: Despite the remarkable agreement between a wide range of SM predictions and their experimental measurements, the SM has to be extended in order to explain the overwhelming experimental evidence from the neutrino oscillation phenomena supporting the existence of neutrino masses and mixings, which are absent in the SM. A simple and natural extension to account for neutrino masses is to introduce right-handed neutrinos in the particle content of the SM. Since these extra right-handed neutrinos are singlets under the SM gauge group, a Majorana mass term for these fermions is therefore allowed in the Lagrangian. One possibility is that this Majorana scale is above the EW scale but in the 100 GeV-TeV range. Then, the masses of the left-handed neutrinos arise in a simple way after ESB through the Weinberg operator in a low scale SM-Seesaw. In this situation, the presence of the new degrees of freedom will induce deviations from unitarity in the leptonic mixing matrix that appears in the charged current interactions. Thus, processes mediated by the weak currents would be modified, and therefore precision measurements of electroweak and flavor observables become a powerful tool to probe for the existence of heavy Majorana neutrinos. Following this idea, a global fit to the most complete and updated stringent set of electroweak and flavour observables to constrain the mixing of the extra heavy right-handed neutrinos in a model independent way has been performed. On the other hand, at some level, the addition of right-handed neutrinos will also impact neutrino oscillation searches. Therefore, the expected sensitivities of new generation of neutrino oscillation experiments to probe for this New Physics will be discussed too.