Hadronic Spectroscopy from the Lattice: Glueballs and Hybrid Mesons

The light hadron spectrum as computed in nonperturbative QCD is reviewed and compared to lattice data and experiment. The mixing of mesons, hybrids and glueballs is calculated in the Field Correlator Method. The strong decay mechanisms are found out in the method and compared to the known phenomenological models. The role of sea quarks (unquenched approximation) is studied analytically using radially excited mesons as an example, and compared to experiment.

We survey the current status of light meson spectroscopy. We begin with a general introduction to meson spectroscopy and and its importance in understanding the physical states of Quantum Chromo Dynamics (QCD). Phemenological models of hadron spectroscopy are described with particular emphasis on the constituent quark model and the qualitative features it predicts for the meson spectrum. We next discuss expectations for hadrons lying outside the quark model, such as hadron st...

Lattice calculations allow us to probe the low-lying, non-perturbative spectrum of QCD using first principles numerical methods. Here we present the low-lying spectrum in the scalar sector with vacuum quantum numbers including, in fully dynamical QCD for the first time, the mixing between glueball, q-qbar, and meson-meson operators.

Mass ratios of glueballs predicted by the latest Lattice QCD calculations in the quenched approximation agree well with four prime experimental candidates.

Recent developments in lattice QCD calculations of the light hadron spectrum and quark masses are reviewed.

Recent lattice simulation studies of heavy-quark hybrid mesons in which the quark and antiquark are bound together by an excited gluon field are summarized.

The lattice gauge theory technique for non-perturbative calculations in QCD is reviewed. The extraction of the continuum limit of lattice results is discussed with particular examples appropriate to hadron spectroscopy (the light hadrons and the glueballs). The determination of the strong coupling constant is presented. The lattice approach to the evaluation of hadronic matrix elements appropriate to weak decays is described.

Recent progress in Lattice QCD is highlighted. After a brief introduction to the methodology of lattice computations the presentation focuses on three main topics: Hadron Spectroscopy, Hadron Structure and Lattice Flavor Physics. In each case a summary of recent computations of selected quantities is provided.

In this paper, I review the experimental situation for both glueballs and hybrid mesons. Theoretical expectations are discussed, and a survey of what is known about hybrid mesons and glueballs is undertaken. Good experimental evidence exists for both states with exotic quantum numbers and a glueball which is mixed with the nearby mesons, but a full understanding of these still requires additional information.

After a brief introduction to hybrid and glueball source operators, I summarize recent lattice results for these particles.