Coulomb energy and gluon distribution in the presence of static sources

We compute the energy of the ground state and a low lying excitation of the gluonic field in the presence of static quark -anti-quark (\qq) sources. We show that for separation between the sources less then a few fm the gluonic ground state of the static \qq system can be well described in terms of a mean field wave functional with the excited states corresponding to a single quasi-particle excitation of the gluon field. We also discuss the role of many particle excitations relevant for large separation between sources.Comment: 14 pages, 11 figure

String-like behaviour of 4d SU(3) Yang-Mills flux tubes

We present here results on the fine structure of the static q\bar q potential in d=4 SU(3) Yang-Mills theory. The potential is obtained from Polyakov loop correlators having separations between 0.3 and 1.2 fermi. Measurements were carried out on lattices of spatial extents of about 4 and 5.4 fermi. The temporal extent was 5.4 fermi in both cases. The results are analyzed in terms of the force between a q\bar q pair as well as in terms of a scaled second derivative of the potential. The data is accurate enough to distinguish between different effective string models and it seems to favour the expression for ground state energy of a Nambu-Goto string.Comment: 9 pages in LaTeX with 2 figures and 2 tables in JHEP style. Replaced to match with shortened published versio

Potential model calculations and predictions for heavy quarkonium

We investigate the spectroscopy and decays of the charmonium and upsilon systems in a potential model consisting of a relativistic kinetic energy term, a linear confining term including its scalar and vector relativistic corrections and the complete perturbative one-loop quantum chromodynamic short distance potential. The masses and wave functions of the various states are obtained using a variational technique, which allows us to compare the results for both perturbative and nonperturbative treatments of the potential. As well as comparing the mass spectra, radiative widths and leptonic widths with the available data, we include a discussion of the errors on the parameters contained in the potential, the effect of mixing on the leptonic widths, the Lorentz nature of the confining potential and the possible $c\bar{c}$ interpretation of recently discovered charmonium-like states.Comment: Physical Review published versio

The static potential: lattice versus perturbation theory in a renormalon-based approach

We compare, for the static potential and at short distances, perturbation theory with the results of lattice simulations. We show that a renormalon-dominance picture explains why in the literature sometimes agreement, and another disagreement, is found between lattice simulations and perturbation theory depending on the different implementations of the latter. We also show that, within a renormalon-based scheme, perturbation theory agrees with lattice simulations.Comment: 18 pages, 11 figures, lattice data of Necco and Sommer introduced, references added, some lengthier explanations given, physical results unchange

Ab Initio Study of Hybrid b-bar-gb Mesons

Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together by the excited gluon field g are studied using the Born-Oppenheimer expansion and numerical simulations. The consistency of results from the two approaches reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio

Chiral Extrapolations and Exotic Meson Spectrum

We examine the chiral corrections to exotic meson masses calculated in lattice QCD. In particular, we ask whether the non-linear chiral behavior at small quark masses, which has been found in other hadronic systems, could lead to large corrections to the predictions of exotic meson masses based on linear extrapolations to the chiral limit. We find that our present understanding of exotic meson decay dynamics suggests that open channels may not make a significant contribution to such non-linearities whereas the virtual, closed channels may be important.Comment: 13 pagers, 2 figure

A numerical study of confinement in compact QED

Compact U(1) lattice gauge theory in four dimensions is studied by means of an efficient algorithm which exploits the duality transformation properties of the model. We focus our attention onto the confining regime, considering the interquark potential and force, and the electric field induced by two infinitely heavy sources. We consider both the zero and finite temperature setting, and compare the theoretical predictions derived from the effective string model and the dual superconductor scenario to the numerical results.Comment: 31 pages, 16 eps figures; v2: references added; v3: footnote added, summation ranges in section 4 made explicit, version published in JHE

Hybrid meson decay from the lattice

We discuss the allowed decays of a hybrid meson in the heavy quark limit. We deduce that an important decay will be into a heavy quark non-hybrid state and a light quark meson, in other words, the de-excitation of an excited gluonic string by emission of a light quark-antiquark pair. We discuss the study of hadronic decays from the lattice in the heavy quark limit and apply this approach to explore the transitions from a spin-exotic hybrid to $\chi_b \eta$ and $\chi_b S$ where $S$ is a scalar meson. We obtain a signal for the transition emitting a scalar meson and we discuss the phenomenological implications.Comment: 18 pages, LATEX, 3 ps figure

On the effective string spectrum of the tridimensional Z(2) gauge model

We study the Z(2) lattice gauge theory in three dimensions, and present high precision estimates for the first few energy levels of the string spectrum. These results are obtained from new numerical data for the two-point Polyakov loop correlation function, which is measured in the 3d Ising spin system using duality. This allows us to perform a stringent comparison with the predictions of effective string models. We find a remarkable agreement between the numerical estimates and the Nambu-Goto predictions for the energy gaps at intermediate and large distances. The precision of our data allows to distinguish clearly between the predictions of the full Nambu-Goto action and the simple free string model up to an interquark distance $r \approx 10/\sqrt{\sigma}$. At the same time, our results also confirm the breakdown of the effective picture at short distances, supporting the hypothesis that terms which are not taken into account in the usual Nambu-Goto string formulation yield a non-trivial shift to the energy levels. Furthermore, we discuss the theoretical implications of these results.Comment: 31 pages, 14 figure

Gluelump Spectrum in the Bag Model

We explore the ordering of the lowest levels in a simple bag model of the ``gluelump'' of Michael and also discuss, again within the context of the bag model, the related problem of hybrid potentials in the limit of very small spacing between quark and anti-quark sources.Comment: 10 page