The theory of weak interactions

Abstract

The weak interactions of leptons are defined by a few principles: lepton conservation, two-component neutrinos and the use of the 1 + γ5 components of electrons and muons. Baryons, pions and kaons interact with leptons through a current whose parity, isotopic spin and strangeness structure is to be determined by experiments on nuclear beta decay, muon capture and leptonic decay of hyperons and mesons. The weak interactions of baryons, pions and kaons among themselves are controlled by a Hamiltonian, whose quantum numbers are likewise to be determined from the pionic decays of kaons and hyperons. This Hamiltonian seems to have a simple structure, defined by the ΔT = ½ rule.The conserved vector current theory successfully defines a part of the weak current, and relates the muon decay rate to the rate of certain allowed Fermi beta decays.Electromagnetic corrections to weak transitions are important and have been estimated, although the calculations present difficulties of principle.Dispersion theory has been applied to the calculation of the weak form factors. Group theoretical speculations may elucidate the structure of the weak currents and suggest the possibility of approximately conserved currents.Cross sections for neutrino capture are small but rise with energy. Neutrinos could also produce intermediate spin 1 mesons, if they exist. Because of their tiny cross sections, zero mass and Fermi statistics, neutrinos play a unique role in astrophysics and cosmology.