Prediction of Double-heavy Tetraquarks Bound States in Quark Model

We present four-body calculations of double-heavy tetraquarks in quark model. Several bound states are found for various flavor combinations. One of them is a strongly bound bbq¯ q¯ with isospin and spin-parity I(J^P) = 0 (1 ⁺) , having a binding energy of almost 200 MeV. This is consistent with the predictions of lattice QCD. We have also found a shallow state for the same I(J^P) = 0 (1 ⁺) channel. By computing density distributions, it is shown that the deep one is a compact tetraquark state, while the shallow one is regarded as a loosely-bound molecule of two color singlet mesons, B and B^∗. This is a hadronic analogue of the cluster formation in light nuclei, the first example that hadrons with totally different nature emerge from a single Hamiltonian.