Empirically Charting Dynamical Chiral Symmetry Breaking

The goal of hadron physics is the provision of a quantitative explanation of the properties of hadrons through a solution of quantum chromodynamics (QCD). This is a fundamental problem that is unique in the history of science: never before have we been confronted by a theory whose elementary excitations are not those degrees-of-freedom readily accessible via experiment. Moreover, QCD generates forces which are so strong that less-than 2 % of a nucleon’s mass can be attributed to the so-called current-quark masses that appear in the QCD Lagrangian; viz., forces that generate mass from almost nothing, a phenomenon known as dynamical chiral symmetry breaking (DCSB). Neither confinement nor DCSB is apparent in QCD’s Lagrangian and yet they play the dominant role in determining the observable characteristics of real-world QCD. The physics of hadrons is ruled by emergent phenomena, such as these, which can only be elucidated through the employment of nonperturbative methods in quantum field theory. This is both the greatest novelty and the greatest challenge within the Standard Model. We must find essentially new ways and means to explain precisely via mathematics the observable content of QCD. Herein we provide a snapshot of recent progress in hadro