Electroweak Unification I
After publication in 1954, the Yang-Mills theory remained for a long time an idea in search of an application.
The success of isotopic spin symmetry had led to a belief that the theory of strong interactions would be the natural field of application. The spin 1 mesons of Figure 2.2 had been identified as the gauge fields of the strong interaction. However, the theory of vector meson dominance had never gone beyond some phenomenological success and limited predictive power.