Eric S. Swanson

On the mechanism of open-flavor strong decays

Open-flavor strong decays are mediated by {ital q{bar q}} pair production, which is known to occur dominantly with {sup 3}{ital P}{sub 0} quantum numbers. The relation of the phenomenological {sup 3}{ital P}{sub 0} model of these decays to {open_quote}{open_quote}microscopic{close_quote}{close_quote} QCD decay mechanisms has never been established clearly. In this paper we investigate {ital q{bar q}} meson decay amplitudes assuming pair production from the scalar confining interaction ({ital sKs}) and from one gluon exchange (OGE). {ital sKs} pair production predicts decay amplitudes of approximately the correct magnitude and {ital D}/{ital S} amplitude ratios in {ital b}{sub 1}{r_arrow}{omega}{pi} and {ital a}{sub 1}{r_arrow}{rho}{pi} which are close to experiment. The OGE decay amplitude is found to be subdominant in most cases, a notable exception being {sup 3}{ital P}{sub 0}{r_arrow}{sup 1}{ital S}{sub 0}+{sup 1}{ital S}{sub 0}. The full {ital sKs} + OGE amplitudes differ significantly from {sup 3}{ital P}{sub 0} model predictions in some channels and can be distinguished experimentally, for example, through an accurate comparison of the {ital D}/{ital S} amplitude ratios in {ital b}{sub 1}{r_arrow}{omega}{pi} and {ital a}{sub 1}{r_arrow}{rho}{pi}. {copyright} {ital 1996 The American Physical Society.}

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.}

Hybrid meson decay phenomenology

The phenomenology of a newly formulated model of hybrid meson decay is developed. The decay mechanism is based on the heavy quark expansion of QCD and the strong coupling flux tube picture of nonperturbative glue. A comprehensive list of partial decay widths of a wide variety of light, s{bar s}, c{bar c}, and b{bar b} hybrid mesons is presented. Results which appear approximately universal are highlighted along with those which distinguish different hybrid decay models. Finally, we examine several interesting hybrid candidates in detail. {copyright} {ital 1999} {ital 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}

Renormalized effective QCD Hamiltonian: Gluonic sector

Extending previous QCD Hamiltonian studies, we present a new renormalization procedure which generates an effective Hamiltonian for the gluon sector. The formulation is in the Coulomb gauge where the QCD Hamiltonian is renormalizable and the Gribov problem can be resolved. We utilize elements of the Glazek and Wilson regularization method but now introduce a continuous cut-off procedure which eliminates non-local counterterms. The effective Hamiltonian is then derived to second order in the strong coupling constant. The resulting renormalized Hamiltonian provides a realistic starting point for approximate many-body calculations of hadronic properties for systems with explicit gluon degrees of freedom. {copyright} {ital 1999} {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.

QCD exotica: Theory perspectives

The current theoretical status of hybrids and glueballs is reviewed. The predictions of bag, constituent glue, and flux tube models of these states are compared to QCD sum rule and lattice gauge theory calculations. Current ideas about the decays of hybrids and glueballs are also discussed.

Hybrids and quark confinement

It has become traditional to assume that the Dirac structure of the phenomenological quark confinement potential is scalar ⊗ scalar. We use the heavy quark expansion of the Coulomb gauge QCD Hamiltonian and the Flux Tube model to demonstrate that this is true but in the effective sense only. The demonstration contains some surprises: confinement is actually vector ⊗ vector and it is nonperturbative mixing between ordinary and hybrid QQ states which generates the scalar-like spin dependent potential at order 1mq2. Thus the existence of hybrids is crucial to establishing well-known spin splitting phenomenology. Finally, the resolution also indicates that the gluonic degrees of freedom in a hybrid must be of a collective nature.