Diquark Correlations in Hadron Physics: Origin, Impact and Evidence

TL;DR

This paper reviews recent theoretical, experimental, and phenomenological evidence indicating that diquark correlations are fundamental to understanding hadron structure, mass generation, and exotic hadron formation.

Contribution

It consolidates diverse evidence to support the significance of diquark correlations in hadron physics and discusses their implications for a unified understanding of hadron structure.

Findings

Diquark correlations are linked to dynamical chiral symmetry breaking.

Experimental signals support the presence of diquarks in proton structure.

Diquarks may be key to forming exotic hadrons like tetraquarks.

Abstract

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.