ABSTRACT
The full electroweak Lagrangian also includes, of course, the couplings of these fields to the quarks and leptons. The first quantum field theory of a weak interaction process was proposed by Fermi for nuclear β-decay, building on the ‘neutrino hypothesis’ of Pauli. The electroweak sector of the Standard Model was originally formulated on the assumption that the three lepton flavours are conserved, and that the neutrinos are massless. It turns out that these two assumptions are related, in the sense that if neutrinos have mass, then (barring degeneracies) ‘neutrino oscillations’ can occur, in which a state of one lepton flavour can acquire a component of another, as it propagates. Non-leptonic weak interactions among hadrons are difficult to analyze quantitatively, though progress can be made via lattice QCD.
