Nobel Lecture: Spontaneous symmetry breaking in particle physics: A case of cross fertilization

I will begin by a short story about my background. I studied physics at the University of Tokyo. I was attracted to particle physics because of the three famous names, Nishina, Tomonaga, and Yukawa, who were the founders of particle physics in Japan. But these people were at different institutions than mine. On the other hand, condensed matter physics was pretty good at Tokyo. I got into particle physics only when I came back to Tokyo after the war. In hindsight, though, I must say that my early exposure to condensed matter physics has been quite beneficial to me. Particle physics is an outgrowth of nuclear physics which began in the early 1930s with the discovery of the neutron by Chadwick, the invention of the cyclotron by Lawrence, and the ı́nvention ’ of meson theory by Yukawa (Nambu, 2007). The appearance of an ever-increasing array of new particles in the subsequent decades, and the advances in quantum Field theory gradu-ally led to our understanding of the basic laws of nature, culminating in the present standard model. When we faced those new particles, our first attempts were to make sense out of them by finding some regularities in their properties. They invoked the symmetry principle to