Images of the Origin of Mass

Recent years have brought considerable progress with studies of the bound-state problem in continuum QCD. A small part of that made with Dyson Schwinger equations is highlighted herein. Topics covered include: opportunities provided by precision experimental studies of the (far) valence region; and capitalising upon new data on hadron elastic and transition form factors.Comment: 7 pages, 3 figures. Contribution to the Proceedings of MENU 2013 - 13th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon, Rome, 30 Sept. - 4. Oct. 201

Confinement, Diquarks and Goldstone's theorem

Determinations of the gluon propagator in the continuum and in lattice simulations are compared. A systematic truncation procedure for the quark Dyson-Schwinger and bound state Bethe-Salpeter equations is described. The procedure ensures the flavour-octet axial-vector Ward identity is satisfied order-by-order, thereby guaranteeing the preservation of Goldstone's theorem; and identifies a mechanism that simultaneously ensures the absence of diquarks in QCD and their presence in QCD$^{N_c=2}$, where the colour singlet diquark is the ``baryon'' of the theory.Comment: 7 pages, LaTeX, uses sprocl.sty and epsfig, contribution to the proceedings of ``Quark Confinement and the Hadron Spectrum'

Hadron Physics: The Essence of Matter

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 a_1-rho 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 F_1^u/F_1^d and G_M^n. 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 \beta-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.Comment: 24 pages, 6 figures, 3 tables. Contribution to the proceedings of the XII Mexican Workshop on Particles and Fields, based on presentations by C.D.Roberts at the Workshop (9-14 Nov. 2009, Mazatlan, Mexico) and at the preceding Mini-School (5-8 Nov. 2009, Culiacan, Mexico)

Flavour decomposition of electromagnetic transition form factors of nucleon resonances

In Poincar\'e-covariant continuum treatments of the three valence-quark bound-state problem, the force behind dynamical chiral symmetry breaking also generates nonpointlike, interacting diquark correlations in the nucleon and its resonances. We detail the impact of these correlations on the nucleon's elastic and nucleon-to-Roper transition electromagnetic form factors, providing flavour-separation versions that can be tested at modern facilities.Comment: Contribution to the proceedings of the 12th Quark Confinement and the Hadron Spectrum (CONF12). Aug. 28 - Sep. 4, 2016. Thessaloniki, Greece. arXiv admin note: text overlap with arXiv:1602.02768, arXiv:1508.0240

Empirically Charting Dynamical Chiral Symmetry Breaking

We provide a snapshot of recent progress in hadron physics made using QCD's Dyson-Schwinger equations, reviewing the generation of a quark anomalous chromomagnetic moment, which may explain the longstanding puzzle of the $a_1$-$\rho$ mass splitting, and the form of the pion and kaon valence-quark parton distribution functions.Comment: 6 pages, 1 figure, 1 table. Contribution to the proceedings of "Achievements and New Directions in Subatomic Physics: Workshop in Honour of Tony Thomas' 60th Birthday," Special Centre for the Subatomic Structure of Matter, Adelaide, South Australia, February 15 - February 19, 2010