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.
Highlights
One of the spectacular successes of this millennium’s hadron spectroscopy experiments is the discovery of many ’exotic’ meson states in the heavy-quark energy region that do not seem to fit into the conventional qqpicture, see e.g. [1–8] for recent review articles
Dynamical chiral symmetry breaking plays an important role for the mass evolution and the structure of the light scalar mesons
The existing work on heavy-light four-quark states using functional methods is based on the four-body approach of Fig. 2, both for systems with a heavy Q Q or Q Q pair [28,29]
Summary
One of the spectacular successes of this millennium’s hadron spectroscopy experiments is the discovery of many ’exotic’ meson states in the heavy-quark energy region that do not seem to fit into the conventional qqpicture, see e.g. [1–8] for recent review articles. One of the spectacular successes of this millennium’s hadron spectroscopy experiments is the discovery of many ’exotic’ meson states in the heavy-quark energy region that do not seem to fit into the conventional qqpicture, see e.g. Some of these carry net electromagnetic charge and may be naturally explained as four-quark states Q Qqq (with q = u, d, s and Q = c, b). Four-quark states are generally considered as promising candidates to explain the structure and properties of these exotic hadrons.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
