The Standard Model (SM) of fundamental interactions

Abstract

Abstract The Standard Model (SM) 2020 of weak, electromagnetic and strong interactions, based on gauge symmetry and spontaneous symmetry breaking, describes all known fundamental interactions at the microscopic scale except gravity and, perhaps, interactions with dark matter. The SM model has been tested systematically in collider experiments, and in the case of strong interactions (quantum chromodynamics) also with numerical simulations. With the discovery in 2012 of the Higgs particle at the Large Hadron Collider (LHC) at the European Council for Nuclear Research (CERN), all particles of the SM have been identified, and most parameters have been measured. Still, the Higgs particle remains the most mysterious particle of the SM, since it is responsible for all the parameters of the SM except gauge couplings and since it leads to the fine-tuning problem. The discovery of its origin, and the precise study of its properties should be, in the future, one of the most important field of research in particle physics. Since we know now that the neutrinos have masses, the simplest extension of the SM implies Dirac neutrinos. With such a minimal modification, consistent so far (2020) with experimental data, the lepton and quark sectors have analogous structures: the lepton sector involves a mixing matrix, like the quark sector (three angles have been determined, the fourth charge conjugation parity (CP) violating angle is still unknown).