IV. A theory of the strong interactions

Abstract

The most promising candidate for a fundamental microscopic theory of the strong interactions is a gauge theory of colored quarks—Quantum Chromodynamics (QCD). There are many excellent reasons for believing in this theory. It embodies the broken symmetries, SU(3) and chiral SU(3)×SU(3), of the strong interactions and reflects the success of (albeit crude) quark models in explaining the spectrum of the observed hadrons. The hidden quantum number of color, necessary to account for the quantum numbers of the low lying hadrons, plays a fundamental role in this theory as the SU(3) color gauge vector ‘gluons’ are the mediators of the strong interactions. The absence of physical quark states can be ‘explained’ by the hypothesis of color confinement, i.e. that hadrons are permanently bound in color singlet bound states. Finally this theory is unique in being asymptotically free, thus accounting for the almost free field theory behavior of quarks observed at short distances.