The LHCb experiment at CERN has discovered a doubly charmed isoscalar tetraquark ${T}_{cc}$ with the quantum numbers of $cc\overline{u}\overline{d}$ and mass about $3875\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, decaying to ${D}^{0}{D}^{0}{\ensuremath{\pi}}^{+}$ through intermediate channel ${D}^{*+}{D}^{0}$. We present study its strange companions $cc\overline{q}\overline{s}$, where $q=u$, $d$ iso...

In this article, we study the mass spectrum of the scalar hidden charm and hidden bottom tetraquark states which consist of the axial-axial type and the vector-vector type diquark pairs with the QCD sum rules. PACS number: 12.39.Mk, 12.38.Lg

The qq spectrum is studied within a chiral constituent quark model. It provides with a good fit of the available experimental data from light (vector and pseudoscalar) to heavy mesons. The new D states measured at different factories are studied. The 0 ++ light mesons are analyzed as q ¯ q pairs or tetraquark structures.

Diquarks are found to have the right degrees of freedom to describe the tetraquark poles in hiddencharm to open-charm meson-meson amplitudes. Compact tetraquarks result as intermediate states in non-planar diagrams of the 1/N expansion and the corresponding resonances are narrower than what estimated before. The proximity of tetraquarks to meson-thresholds has an apparent role in this analysis ...

We present a detailed analysis of the symmetry properties of a four-quark wave function and its solution by means of a variational approach for simple Hamiltonians. We discuss several examples in the light and heavy-light meson sector.