In Chapter 5, we learned a great deal about the dynamics of quantum chromodynamics. In Section 4.5, we argued that the hierarchy problem is one of the puzzles of the Standard Model. The grand unified models of the previous chapter provided a quite stark realization of the hierarchy problem. In an SU(5) grand unified model, we saw that it is necessary to carefully adjust the couplings in the Higgs potential in order that one obtain light doublets and heavy color triplet Higgs. This is already true at tree level; loop effects will correct these relations, requiring further delicate adjustments.

The first proposal to resolve this problem goes by the name “technicolor” and is the subject of this chapter. The technicolor hypothesis exploits our understanding of QCD dynamics. It elegantly explains the breaking of the electroweak symmetry. It has more difficulty accounting for the masses of the quarks and leptons, and simple versions seem incompatible with precision studies of the W and Z particles. In this chapter, we will introduce the basic features of the technicolor hypothesis. We will not attempt to review the many models that have been developed to try to address the difficulties of flavor and precision electroweak experiments. It is probably safe to say that, as of this writing, none is totally successful, nor are they terribly plausible. But it should be kept in mind that this may reflect the limitations of theorists; experiment may yet reveal that nature has chosen this path. In the second part of this book, we will argue that in string theory, ignoring phenomenological details, a technicolored solution to the hierarchy problem seems as likely as its main competitor, supersymmetry.