Quantum Chromodynamics, the theory of quarks and gluons, whose interactions can be
described by a local SU (3) gauge symmetry with charges called “color quantum numbers” …

The existence and properties of the sigma meson have been controversial for almost six
decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the …

This biennial Review summarizes much of particle physics. Using data from previous
editions, plus 2158 new measurements from 551 papers, we list, evaluate, and average …

We highlight the progress, current status, and open challenges of QCD-driven physics, in
theory and in experiment. We discuss how the strong interaction is intimately connected to a …

Glueballs, hybrids and multiquark states are predicted as bound states in models guided by
quantum chromo dynamics (QCD), by QCD sum rules or QCD on a lattice. Estimates for the …

Calculations within QCD (lattice and sum rules) find the lightest glueball to be a scalar with
mass in the range of about 1000–1700 MeV. Several phenomenological investigations are …

Using an effective σ/f 0 (500) resonance, which describes the π π→ π π and γ γ→ π π
scattering data, we evaluate its contribution and the ones of the other scalar mesons to the …

We discuss theoretical predictions for the existence of exotic (non-quark-model) mesons and
review prominent experimental candidates. These are especially the f0 (1500) and f0 (1710) …

We show that two nonets and a glueball provide a consistent description of data on scalar
mesons below 1.7 GeV. Above 1 GeV the states form a conventional q bar q nonet mixed …

Glueballs and other resonances with large gluonic components are predicted as bound
states by Quantum Chromodynamics (QCD). The lightest (scalar) glueball is estimated to …