Structure of open-flavour four-quark states in the charm and bottom region

We present quantitative results for masses and the internal structure of four-quark states with two heavy quarks, i.e. $QQ'\bar{q}\bar{q}'$ with $Q,Q'\in \{c,b\}$ and $q,q' \in \{u,d,s\}$, and $J^{P} \in {1^+}$. The composition of these states in terms of meson-meson and diquark-antidiquark pairs, extracted from a relativistic four-body Faddeev-Yakubowski equation, is dynamically determined from underlying QCD forces. We find states at energy levels in very good agreement with lattice QCD and, where available, with experimental states. Their internal structure, most notably between the $T^+_{cc}$, $T_{bc}$ and $T^-_{bb}$, show significant and sizeable variations.