ENCORE · Exploring Neutrinos: Cosmology, Oscillations, REactors

Exploring Neutrinos: Cosmology, Oscillations, REactors

The so-called Standard Model (SM) of particle physics is the theory that describes how fundamental forces act on all of the matter particles. It has successfully explained almost all experimental results, such as those from the LHC accelerator, but it does not provide answers to other phenomena such as the existence of dark matter or neutrino oscillations. The most elusive of all known elementary particles, neutrinos come in three types or flavors (electron, muon and tau). Experimental results have provided evidence that neutrinos change (or oscillate) flavor during their propagation, which implies that neutrinos are massive, a fact that is not explained in the SM. After fifty years of experimental results, most neutrino properties are well measured. There are, however, some that we still ignore, such as their absolute mass scale, how their masses are ordered or whether additional neutrino states exist beyond the standard three (they would be insensitive to weak interactions or “sterile”). Knowledge of these quantities is necessary for a better understanding of particle physics, and they may indicate us the direction where to best look for new physics beyond the SM. The ongoing experimental efforts need a theoretical input in order to fully exploit the observations, and the measurements from different probes provide maximal information only when combined together. The global objective of the Proposal was to provide theoretical results which could help to better understand neutrino physics, focusing on three aspects: cosmology, oscillations and nuclear reactors. The objectives of the Action can be divided in two categories: new theoretical calculations and phenomenological analyses of experimental data. Concerning neutrino cosmology, we performed improved calculations of both full active-sterile neutrino oscillations in the early Universe and the local overdensity of relic neutrinos near the Earth. We also compared the reactor antineutrino spectrum with new estimates from running experiments and found new global analyses of neutrino data that lead to updated constraints on the oscillation parameters and mass properties, including the ordering and the absolute scale of neutrino masses, for the cases of three and four neutrinos. Our results also include the first application in a cosmological context of a statistics method meant to derive prior-free results in the context of Bayesian analyses. To summarize, the Action helped to fill some missing pieces of information and to increase our knowledge of neutrinos and their properties.

Data: CORDIS, © European Union