Hadron Physics: The Essence of Matter

Abstract

Dynamical chiral symmetry breaking (DCSB) is a remarkably effective mass generating mechanism. It is also, amongst other things, the foundation for a successful application of chiral effective field theories, the origin of constituent‐quark masses, and intimately connected with confinement in QCD. Using the Dyson‐Schwinger equations (DSEs), we explain the origin and nature of DCSB, and elucidate some of its consequences, e.g.: a model‐independent result for the pion susceptibility; the generation of a quark anomalous chromomagnetic moment, which may explain the longstanding puzzle of the a1‐ρ mass splitting; its impact on the behaviour of the electromagnetic pion form factor—thereby illustrating how data can be used to chart the momentum‐dependence of the dressed‐quark mass function; in the form of the pion and kaon valence‐quark parton distribution functions, and the relation between them; and aspects of the neutron’s electromagnetic form factors, in particular F1u/F1d and GMn. We argue that in solving QCD, a constructive feedback between theory and extant and forthcoming experiments will most rapidly enable constraints to be placed on the infrared behaviour of QCD’s β‐function, the nonperturbative quantity at the core of hadron physics; and emphasise throughout the role played by confrontation with data as a means of verifying our understanding of Nature.