Four-quark states from functional methods

Abstract

In this feature article we summarise and highlight aspects of the treatment of four-quark states with functional methods. Model approaches to those exotic mesons almost inevitably have to assume certain internal structures, e.g. by grouping quarks and antiquarks into (anti-)diquark clusters or heavy-light $q\bar{q}$ pairs. Functional methods using Dyson-Schwinger and Bethe-Salpeter equations can be formulated without such prejudice and therefore have the potential to put these assumptions to test and discriminate between such models. So far, functional methods have been used to study the light scalar-meson sector and the heavy-light sector with a pair of charmed and a pair of light quarks in different quantum number channels. For all these states, the dominant components in terms of internal two-body clustering have been identified. It turns out that chiral symmetry breaking plays an important role for the dominant clusters in the light meson sector (in particular for the scalar mesons) and that this property is carried over to the heavy-light sector. Diquark-antidiquark components, on the other hand, turn out to be almost negligible for most states with the exception of open-charm heavy-light exotics.

19 pages, 9 figures, v2: typos corrected, version accepted by Few Body Syst

References in corpus (21)

• Multiquark Resonances
• Pentaquark and Tetraquark states
• Exotics: Heavy Pentaquarks and Tetraquarks
• Charmonium
• Baryons as relativistic three-quark bound states
• Discovery of doubly-charmed Xi_{cc} baryon implies a stable (b b ubar dbar) tetraquark
• Heavy-quark symmetry implies stable heavy tetraquark mesons $Q_i{Q}_j{\bar{q}}_k{\bar{q}}_l$
• A Theory of Scalar Mesons
• Nature of the f_0(600) from its N_c dependence at two loops in unitarized Chiral Perturbation Theory
• Exotic tetraquark states with the $qq\bar{Q}\bar{Q}$ configuration
• Lattice QCD investigation of a doubly-bottom $\bar{b}\bar{b}ud$ tetraquark with quantum numbers $I(J^P)=0(1^{+})$
• Mixing of scalar tetraquark and quarkonia states in a chiral approach
• Study of the $Z_c^{+}$ channel using lattice QCD
• Lattice study of light scalar tetraquarks with I=0,2,1/2,3/2: are sigma and kappa tetraquarks?
• Experimental status of the $\pi \pi$ isoscalar S wave at low energy: $f_0(600)$ pole and scattering length
• On the spectral functions of scalar mesons
• Spectra of heavy mesons in the Bethe-Salpeter approach
• On light baryons and their excitations
• Exciting flavored bound states
• Mass spectra and Regge trajectories of light mesons in the Bethe-Salpeter approach
• Covariant equations for the tetraquark and more

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• Four-quark states with charm quarks in a two-body Bethe-Salpeter approach
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• The rainbow modified-ladder approximation and degenerate pion
• Unified tetraquark equations
• Glueballs from bound state equations
• Meson scattering and tetraquarks in two-dimensional QCD
• Scattering of mesons and emergence of tetraquarks in two-dimensional QCD