We construct mass terms for the Standard Model fermions of the first generation. This includes the neutrino, where we invoke either a dimension-5 term or we add a right-handed neutrino field. We reconsider the CP symmetry, the fate of baryon and lepton numbers, and the quantization of the electric charge. The question of the mass hierarchy takes us to the seesaw mass-by-mixing mechanism. As a peculiarity, we finally revisit such properties in the scenario without colors (Nc=1), which allows leptons and baryons to mix.

This concluding chapter recaps what has been learnt in the previous chapters about the Standard Model. This model is highly successful in describing particle physics phenomena. Some of its successes are briefly underlined, such as the number of light neutrino families. However, as with any model, it also has its weaknesses, which are also provided. The most important open questions of particle physics are addressed in the second part of the chapter, in particular, the matter–antimatter asymmetry, the hypothetical presence of the dark matter. Possible extensions of the Standard Model are presented to incorporate massive neutrinos.