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Neutrinos

During the last decade, the evidence for flavour oscillations in atmospheric and solar neutrinos has been confirmed in accelerator and reactor experiments. The immediate consequence is that neutrinos are massive and mix, and therefore new physics beyond the Standard Model (SM) is called for. The interplay between particle physics and cosmology and astrophysics is inherent in the study of neutrino physics, and in our group there are contributions in both sides.

  • Neutrino phenomenology

 

Members of our group have liderated the analysis of present and future oscillation experiments (solar, atmospheric, reactor and accelerator) to determine the parameters of the lepton sector. Future experiments that may lead to the discovery of CP violation in the neutrino sector are currently being discussed. Members of our team have contributed decisevely to the analysis of the real potential of these big projects: Super-beams, Beta-beams and neutrino factories. In particular, P. Hernández is the principal organizer of the European project EUROnu "A High Intensity Neutrino Oscillation Facility in Europe", recently approved.

In the context of particle physics, members of our group have proposed and studied extensions of the SM that try to explain neutrino masses and their mixings and, if possible, address other issues such as the hierarchy problem or the dark matter of the Universe (with supersymmetry or extra dimensions). In these extensions, new TeV scale particles are predicted and could be produced at the LHC.

Neutrinos have outstanding implications in astrophysics and cosmology. In particular, members of the group liderate theoretical calculations of solar neutrino fluxes, trying to find a solution to the solar composition problem. Propagation of high energy neutrinos from their source and their connection to extragalactic cosmic rays is also studied in the group. Other members have studied the possibility to measure the neutrino flux using neutrino experiments from hypothetical annihilations of dark matter particles in the Sun. In cosmology, large scale structure formation imposes strong constraints on the scale of neutrino masses, that can be larger than the laboratory ones (Tritium beta-decay, for instance), and it is also a matter of study of the group.

  • Leptogenesis

Leptogenesis is a theoretical mechanism that tries to explain the origin of the matter-antimatter asymmetry of the Universe through heavy Majorana neutrino decays in the Early Universe, which would imply lepton number violation. As in the SM sphaleron processes preserve baryon minus lepton number, this lepton asymmetry would be converted to a baryon one. For the neutrino masses obtained from oscillation experiments, in the context of the Seesaw mechanism, the value of the ratio between the density of baryons and that of photons is obtained naturally, independently of initial conditions. Members of our group have studied the possible connection between the CP violation phases in leptogenesis and at low energies, as well as the regions of the parameter space in the context of supersymmetry that give lepton flavour violation in future charged lepton precision experiments.

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