V-A theory: a view from the outside

To me the most impressive thing about the V -A theory is that it was formulated in the face of experimental results that did not support its predictions. In physics experiments are expected to give guidance to theorists. Sometimes an experiment may itself be wrong, but then it is the responsibility of other experiments to “weed out” the wrong experiment. On the other hand, when repeated experiments stand by a result, it is generally foolish to propose a theory that contradicts the accepted experimental results. However, this is exactly what Sudarshan and Marshak did in proposing the V -A theory simply because they had a desire to have a universal theory of weak interactions and the predictions of their theory were subsequently vindicated by more careful experiments. Basically, there was a combination of wrong experiments that had completely dominated the physics scene before the V -A theory.

So, for example in the decay of He6 (which is a Gammow-Teller decay), λ was determined to have the value λ = 1/3 so that one would conclude the coupling for Gamow-Teller transitions to be primarily of T type [5]. [5] Rustad B M and Ruby S L 1955 Phys. Rev. 97, 991

Thus, the dominant sentiment in the theoretical physics community at the time was that the generalized Fermi theory with S, T couplings was responsible for the weak decays.

Then came the proposal by Lee and Yang [8] that parity is violated in weak interactions which was soon [9] established in the Gamow-Teller decay of Co60 which also showed that parity is violated maximally in these decays....As a result, experiments needed to be analyzed afresh.