QCD forces and heavy quark bound states

Abstract

The present knowledge of QCD confining forces between static test charges is summarised, with an emphasis on lattice results. Recent developments in relating QCD potentials to quarkonium properties by use of effective field theory methods are presented. The validity of non-relativistic QCD and the adiabatic approximation with respect to heavy quark bound states is explored. Besides the static potential and relativistic correction terms, the spectra of glueballs and gluinoballs, hybrid excitations of the QCD flux tube between fundamental colour sources, potentials between charges in various representations of the SU (3) gauge group, and multi-particle interactions are discussed. Implications for quarkonia systems and quark-gluon hybrid mesons are drawn. *

Multi-quark interactions with a globally stable vacuum

“…On the other hand, with these counting rules the Lagrangians L H and L 8q contribute at the same N c order, thus the effects coming from them are comparable and must be considered together. 3 It is clear that our considerations are also relevant if the multi-quark interactions create a hierarchy [23] similar to the hierarchy found within the gluon field correlators [24]. In this case the lowest four-quark interaction forms a stable vacuum corresponding to spontaneously broken chiral symmetry.…”

Diquark and light four-quark states

“…The diquark cluster is regarded as a constituent similar to a constituent quark. The strong dynamics between the diquark and the anti-diquark in tetraquark states is supposed to be similar to that between the quark and the anti-quark in mesons [50,51]. As an approximation, the masses of diquarks obtained with sum rule approach are regarded as the constituent masses in constituent quark model.…”

The flux distribution of the three quark system in SU(3)

“…The question, however, hasn't been settled yet. Some authors support the ∆Ansatz [3,4], others find evidence for the Y Ansatz [6] (see also [5]). This discrepancy is due to the difficulty of measuring the 3Q potential accurately for a large quark separation and moreover the difference between the two Ansätze in the 3Q potential is not large, at most 20%.…”

“…In order to distinguish between the two Ansätze, the 3Q potential was investigated using lattice simulations by several groups more than 15 years ago [1,2] and also recently [3,4,5,6]. The question, however, hasn't been settled yet.…”