Adam Szczepaniak

Glueball spectroscopy in a relativistic many-body approach to hadronic structure.

A comprehensive, relativistic many-body approach to hadron structure is advanced based on the Coulomb gauge QCD Hamiltonian. Dynamical chiral symmetry breaking naturally emerges, and both quarks and gluons acquire constituent masses when standard many-body techniques are employed. Gluonia are studied both in the valence and in the collective, random phase approximations. Calculated quenched glueball masses are found to be in remarkable agreement with lattice gauge theory when using representative values for the strong coupling constant and string tension. {copyright} {ital 1996 The American Physical Society.}

On the Dirac structure of confinement

The Dirac structure of confinement is shown to be of a timelike-vector nature in the heavy quark limit of QCD. This stands in contradiction with the phenomenological success of the Dirac scalar confining potential. A resolution is achieved through the demonstration that an effective scalar interaction is dynamically generated by nonperturbative mixing between ordinary and hybrid Q{bar Q} states. The resolution depends crucially on the collective nature of the gluonic degrees of freedom. This implies that dynamical gluonic effects are vital when attempting to incorporate fine structure in models of the Q{bar Q} interaction. {copyright} {ital 1997} {ital The American Physical Society}

From current to constituent quarks: A renormalization-group-improved Hamiltonian-based description of hadrons

A model which combines the perturbative behavior of QCD with low-energy phenomenology in a unified framework is developed. This is achieved by applying a similarity transformation to the QCD Hamiltonian which removes interactions between the ultraviolet cutoff and an arbitrary lower scale. Iteration then yields a renormalization-group-improved effective Hamiltonian at the hadronic energy scale. The procedure preserves the standard ultraviolet behavior of QCD. Furthermore, the Hamiltonian evolves smoothly to a phenomenological low-energy behavior below the hadronic scale. This method has the benefit of allowing radiative corrections to be directly incorporated into nonperturbative many-body techniques. It is applied to Coulomb gauge QCD supplemented with a low-energy linear confinement interaction. A nontrivial vacuum is included in the analysis via a Bogoliubov-Valatin transformation. Finally, the formalism is applied to the vacuum gap equation, the quark condensate, and the dynamical quark mass. {copyright} {ital 1997} {ital The American Physical Society}

Decays of hybrid mesons

The heavy quark expansion of Quantum Chromodynamics and the strong coupling flux tube picture of nonperturbative glue are employed to develop the phenomenology of hybrid meson decays. The decay mechanism explicitly couples gluonic degrees of freedom to the pair produced quarks and hence does not obey the well known, but model-dependent, selection rule which states that hybrids do not decay to pairs of L = 0 mesons. However, the nonperturbative nature of gluonic excitations in the flux tube picture leads to a new selection rule: light hybrids do not decay to pairs of identical mesons. New features of the model are highlighted and partial widths are presented for several low lying hybrid states. Typeset using REVTEX 1

QCD HAMILTONIAN APPROACH FOR THE GLUEBALL SPECTRUM

Abstract A new, comprehensive relativistic many-body approach utilizing the Coulomb gauge QCD Hamiltonian is advanced for hadron physics. The formalism properly incoporates renormalization for regularizing divergences and also manifests the Nambu-Goldstone realization of chiral symmetry. Using standard many-body techniques, calculations for the constitutuent quark, gluon condensates and masses and gluon spectrum are found to be in good agreement with QCD sum-rules and quenched lattice gauge results.

Relativistic quark model description of baryon properties

Using a relativistic quark model approach that successfully described flavored meson systems, electromagnetic form factors and structure functions are calculated for the low mass baryons. The observed proton, neutron and lambda moments, rms radii and form factors are all reproduced and predictions are made for other baryon observables which will be measured at CEBAF. Most significantly, by properly including the quark potential energy the long standing neutron to proton structure function ratio anomaly for x∼1 has been resolved.

Glueball spectroscopy in a many body QCD Hamiltonian approach

The low-lying glueball mass spectrum is calculated utilizing a new, comprehensive, relativistic many-body approach based upon the Coulomb gauge QCD Hamiltonian. Central to the formalism is the renormalization procedure for regularizing divergences and the Nambu-Goldstone realization of chiral symmetry. Standard many-body techniques are adopted to compute the constituent quark, gluon masses and condensates and glueball spectrum. Results are in good agreement with QCD sum-rule and quenched lattice gauge theory.

On the constituent quark structure

We investigate the constituent quark substructure by determining the energy distribution of a light QCD quark in a static chromoelectric field. Nontrivial structure of the constituent quark is found and the perturbative QCD evolution of the energy distribution amplitude is detailed.

Relativistic Quark Model Baryon Analysis

Using a relativistic quark model approach that successfully described flavored meson systems, electromagnetic form factors and structure functions are calculated for the low mass baryons. The observed proton, neutron and lambda moments, rms radii and form factors are all reproduced and predictions are made for other baryon observables which will be measured at CEBAF. Most significantly, by properly including the quark potential energy the long standing neutron to proton structure function ratio anomaly for x ~ 1 has been resolved.