Neutrinos as cosmic messengers

I briefly review the current status of neutrino oscillation parameters and discuss the role of neutrinos as cosmological probes, that could possibly induce the baryon asymmetry as well as the dark matter in the Universe. I comment on the origin of neutrino masses in seesaw-type and low-scale models and mention some of their laboratory signals. STATUS OF NEUTRINO OSCILLATIONS The discovery of neutrino oscillations marks a turning point in particle physics as it implies that neutrinos have masses. Given their weak interaction, neutrinos play a special role as cosmic probes as they may provide information about very early stages of the evolution of the Universe. Last, but not least, understanding their properties may provide a valuable clue of what may lie ahead of the Standard Model (SM) of basic interactions. Here I summarize the status of the neutrino oscillation results after the Neutrino 2008 conference [1], given in Ref. [2]. Evidence for neutrino oscillations coming from “celestial” (solar and atmospheric) neutrinos is unambiguously confirmed by “laboratory” neutrinos produced at reactors and accelerators. The basic theoretical layout for the description of neutrino oscillation data has been given almost thirty years ago and involves the concept of the lepton mixing matrix, the lepton analogue of the quark mixing matrix. In its simplest unitary 3-dimensional form is given as [3]