Large-$N_c$ QCD and tetraquarks

Abstract

Tetraquark properties are examined in the limit of large $N_c$ of color in QCD. The qualitative differences between molecular and compact tetraquarks are outlined. Consequences of the possible existence of compact tetraquarks are analyzed and shown to lead to upper bounds in the $N_c$-behavior of their decay widths. Open questions on theoretical grounds, related to the dynamics of systems composed of two quarks and two antiquarks, are addressed.

Comments: 12 pages, 10 figures. Plenary talk given at the Conference Quark Confinement and the Hadron Spectrum XIII, 31 July - 6 August 2018, Maynooth, Ireland