28 - Panel Session: Spontaneous Breaking of Symmetry

Summary

This panel was intended to function as a discussion, but instead it emerged as a series of short presentations by the participants Robert Brout, Tian Yu Cao, and Peter Higgs, with an introductory discussion by the chair. The present chapter consists of a revised and edited version of those reports and also includes a later submission by Yoichiro Nambu, who was scheduled to be on the panel originally but was unable to attend.

Introduction

The two sectors of the current Standard Model of particle physics, the strong color and the electroweak sectors, are distinct and are tied together only by ontology. Together, they describe the interactions, other than gravitation, of the three generations of quarks and leptons. The dream of representing the strong and weak “nuclear” interactions (as they were known before the acceptance of the quarks) as quantum field theories (QFT) goes back to the 1930s. The first such QFT, other than quantum electrodynamics, was Enrico Fermi's weak-interaction theory of 1934. This theory was almost immediately extended by Werner Heisenberg in 1935 to include the strong interactions (thus making it the first unified QFT) whose exchanged “quanta” were those of the electron-neutrino “Fermi-field.” In 1935, Hideki Yukawa invented “U-quanta,” now called pions, to represent the field of strong interactions, adjusting their mass to fit the range of nuclear forces. This was again a unified QFT, as the U-quanta were also intended to serve as intermediate bosons of the weak interaction.