Topics in QCD Modeling of Hadron Physics

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The mechanisms underlying hadron physics in terms of bound states of quarks and gluons are investigated. The particular approach used here is a nonperturbative modeling of hadrons and hadronic processes based on the Dyson-Schwinger equations of the underlying field theory. It hasparticular advantages when the substructure of subatomic particles is probedby the high energy scattering and significant recoil of beams of electrons; the demands of relativity, important broken symmetries, and the non-observation of quarks and gluons are easily incorporated. Established perturbative behavior of the field theory is also preserved. This research will extend the current reach of such an approach, and critically examine short-comings, through an exploration of a number of topics. These includethe quark mass dependence of observables up through the charm quark region, and an analysis of lattice-QCD results for intermediate elements, such asquark propagators and quark-gluon vertices. An improved description of the quark-gluon vertex is of primary interest since it controls the corrections to the common ladder-rainbow approximation. The momentum scale at which the pion charge form factor gives way to perturbative behavior is also of majorinterest. Other topics include an analysis of quark propagators from full-QCD lattice simulations, the use of an algebraic model to estimate the strange quark content of the magnetic moment of the nucleon and toexplore high order corrections to ladder-rainbow approximation, the quark mass dependence of meson structure observables, radiative transitions of heavy quark mesons, and the extraction of nonperturbative physics from quark current correlations. Broader impacts of the program include the cross-fertilization of nuclear and particle physics, a return on the investment in the experimental facilities of subatomic science, integration of research and teaching, and wide dissemination of scientific results. PhD students working on this project contribute to undergraduate education through their teaching of undergraduate laboratory or recitation sections. We foster interactions between the PhD students and experienced researchers as a contribution to the nation's research and education infrastructure. The PI uses examples from this research program to illustrate key elements of core graduate classes in Quantum Mechanics and Nuclear and Particle Physics. The PI and a colleague supervise an informal seminar course for graduate students and postdoctoral associates to discuss and present aspects of QCD and field theory that are outside graduate coursework but nevertheless central to cutting edge research. The PI is also active in a re-structuring of the local undergraduate physics curriculum for majors; a particular interest is the development of a freshman seminar course to discuss current events of discovery and breakthrough in physics and related science.