Are there compact heavy four-quark bound states?

Abstract

We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, nonmolecular, four-quark bound states. While $QQ\overline{n}\overline{n}$ states may be stable in nature, the stability of $Q\overline{Q}n\overline{n}$ states would imply the existence of quark correlations not taken into account by simple quark dynamical models.