Diquark correlations in hadron physics: Origin, impact and evidence

The last decade has seen a marked shift in how the internal structure of hadrons is understood. Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularised QCD have provided strong indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in the flavour-separation of the proton's electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic tetra- and penta-quark hadrons. A broad spectrum of such information is evaluated herein, with a view to consolidating the facts and there from moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play. (C) 2020 Published by Elsevier B.V.

Automated summary

In the past decade, there has been a significant shift in understanding the internal structure of hadrons, with new theoretical techniques and experimental findings suggesting that soft quark+quark (diquark) correlations play a crucial role in hadron physics. These correlations are believed to be a necessary consequence of dynamical chiral symmetry breaking and may be critical for the formation of exotic tetra- and penta-quark hadrons.