The Universal Fermi Interaction and the Conserved Vector Current in Beta Decay

As early as 1948 the great similarity in the strength of the coupling constants in beta decay, muon decay, and muon capture had tempted several authors' to postulate a universal Fermi interaction. This view was later reviewed extensively in a series of lectures' by Fermi. However, any universality should imply not only the equality of the coupling constants, but also the similarity of the structure of the interactions. For a long time there was no conclusive evidence to substantiate the latter. Then came the discovery of the nonconservation of parity in beta decay and also in p decay in 1957. Following the tremendous activity of that period, overwhelming evidence showed that the interaction form of four fermions such as in nuclear beta decay and muon decay can be represented by a (V — A) interaction.