How many new particles do we need after the Higgs boson?

Abstract

The discovery of the scalar boson completes the experimental confirmation of the particles predicted by the Standard Model, which achieves to describe almost all phenomena observed in nature in terms of a few symmetry principles and a handful of numbers, the constants of nature. Neutrino oscillations are the only confirmed piece of evidence for physics beyond the Standard Model found in the laboratory. They can easily be explained if the neutrinos have partners with right handed chirality like all other fermions. Remarkably, right handed neutrinos can simultaneously explain long standing puzzles from cosmology, namely Dark Matter and the baryon asymmetry of the universe. I discuss how close this minimal extension of the Standard Model by right handed neutrinos can bring us to a complete theory of nature and what else may be needed.