2021

Barabanov, M.Yu.; Bedolla, M.A.; Brooks, W.K.; Cates, G.D.; Chen, C.; Chen, Y.; Cisbani, E.; Ding, M.; Eichmann, G.; Ent, R.; Ferretti, J.; Gothe, R.W.; Horn, T.; Liuti, S.; Mezrag, C.; Pilloni, A.; Puckett, A.J.R.; Roberts, C.D.; Rossi, P.; Salmé, G.; Santopinto, E.; Segovia, J.; Syritsyn, S.N.; Takizawa, M.; Tomasi-Gustafsson, E.; Wein, P.; Wojtsekhowski, B.B.

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 therefrom moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play.