Gauge theories of weak interactions

The purpose of these notes is to produce an introduction to the presently popular standard model of weak and electromagnetic interactions. This model has a number of ingredients, leptons, quarks, vector bosons, photons and finally also Higgs scalars, and of these only the leptons and photons are directly observed particles. The evidence for quarks comes from another domain of physics, namely strong interactions supposedly described by quantum chromodynamics. The massive vector bosons as well as the Higgs particles are theoretical inventions, and while few people doubt the existence of vector bosons, many are skeptical with respect to the Higgs system. Meanwhile, theorists have gone beyond the standard model, and speculations on possible grand unified schemes have emerged. Also there are speculations on the possible compositeness of quarks and leptons, or Higgs particles