Hadron Physics from Covariant QCD Modeling

Kent State University, Kent OH

Investigators

Abstract

Project Summary This proposal requests three yeas of support to continue a research program involving one senior investigator, one postdoctoral fellow and several students. The research will address hadrons and hadronic processes in terms of the con.ned quarks and gluons of Quantum Chromodynamics (QCD)b y joining recent advances in understanding the propagators and vertices involving gluon, ghost and quark .elds with advances in covariant modeling of mesons, form factors and interactions. The principal investigator has expertise in continuum nonperturbative QCD modeling of hadrons and the subsequent description of hadronic processes based on the Dyson-Schwinger equations of the theory. Previous work has concentrated upon the solution of the Dyson- Schwinger equation for the dressed quark propagator followed by the solution of the bound state Bethe-Salpeter equation for mesons. The e.ective interaction that has emerged preserves the perturbative short distance behavior of QCD while the perturbative domain is described with two parameters. It generates the empirical amount of dynamical chiral symmetry breaking and the closely related phenomena of absolute quark con.nement is implemented. The evident success of this approach for the ground state pseudoscalar and vector mesons of light quarks, and for baryons, needs to be reconciled with recent advances by others that have increased our understanding of the gauge boson sector of QCD. In particular, we seek to replace the two parameters of the above-mentioned e.ective interaction by results of independent studies of the more fundamental gauge boson sector of QCD. There are available model solutions of the gauge sector Dyson-Schwinger equations for at least the gluon and ghost dressed propagators that we wish to connect to. Also there is available independent quality data from lattice simulations of QCD for these quantities and for the important gluonquark vertex. Thus the time is ripe for development of continuum models of hadronic processes constrained by QCD data. These issues relate to the origin of quark con.nement and dynamical chiral symmetry breaking. Information on how to move beyond the ladder approximation is at hand and will be used. The consequences will be subjected to an evaluation in terms of hadronic observables. This information is needed to both advance our understanding of hadron physics and learn about the physically relevant nonperturbative dynamics of the gauge sector of QCD. Our combined approach will be an advance in continuum Poincare invariant investigations of the dominant quark-gluon mechanisms underlying hadron physics. Several activities within this project have broader impact. The research undertaken with this grant helps to advance both nuclear and particle physics. The quark-gluon basis of hadronic properties and processes is a focus area of nuclear physics and theoretical progress contributes to the return on the investment in the experimental facilities at JLab and RHIC. This work also contributes to the integration of research and education through the training of graduate students and postdoctoral scholars, and through the involvement of graduate students and postdoctoral scholars in undergraduate teaching. Also students get the opportunity to participate in professional meetings. The international collaborations with scientists at the University of Tuebingen, Germany, needed to carry out parts of this project contribute to the nation's infrastructure for research and education.