Strongly Coupled Gauge Theories

The theory of the strong interaction, QCD, explains how most of the mass we observe in the Universe is generated through gauge theory dynamics and lies far below the scale of any new physics, such as the Planck mass associated with quantum gravity. Lattice QCD simulations have made this explanation quantitatively precise and also hint at why some quarks are much lighter still. They are providing reliable predictions for much more besides, enabling precision tests of the Standard Model and imposing constraints on physics beyond. It is worth asking whether the mass scales associated with electroweak symmetry breaking and the heavier quarks could also be explained by a new gauge dynamics. Lattice simulations are now venturing to explore this theoretical territory, which is intrinsically non-perturbative.