Stability of Heavy Tetraquarks
Résumé
We discuss the stability of tetraquark systems with two different masses. After some reminders about the stability of very asymmetric $QQ{\bar{q}} {\bar{q}}$ tetraquarks, we demonstrate that in the all-heavy limit $q \rightarrow Q$ , the system becomes unstable for standard color-additive models. We also analyze the consequences of symmetry breaking for $Qq{\bar{Q}}{\bar{q}}$ configurations: we find a kind of metastability between the lowest threshold $Q{\bar{Q}} + q{\bar{q}}$ and the highest one, $Q{\bar{q}}+{\bar{Q}} q$ , and we calculate the width of the resonance. Our results are consistent with the experimental observation of narrow hadrons lying well above their lowest decay threshold.