ABSTRACT
This chapter discusses the construction of effective weak Hamiltonians, introducing the operator product expansion and the renormalisation group. Heavy-quark effective theory and heavy-quark expansion are later developments that have been established in the second half of the eighties and at the beginning of the nineties. The central goal is the investigation of flavour physics, the most complicated sector in the understanding of fundamental interactions. A good example is give by particle-antiparticle mixing, as first studied with neutral kaons. Computing weak decays of hadrons is a complicated problem in quantum field theory. The idea of factorisation, in various forms and generalisations, is the key to essentially all applications of perturbative quantum chromo-dynamics (QCD), including the important areas of deep-inelastic scattering and jet or lepton pair production in hadron-hadron collisions. The QCD factorisation approach as encoded in may be viewed as a consistent formalisation and generalisation of Bjorken’s colour transparency argument.
