Double-heavy tetraquarks

Abstract

In the framework of the chiral quark model along with complex scaling range, we perform a dynamical study on the low-lying $S$-wave double-heavy tetraquark states ($QQ\overline{q}\overline{q}$, $Q=c$, $b$ and $q=u$, $d$) with an accurate computing approach, Gaussian expansion method. The meson-meson and diquark-antidiquark configurations within all possible color structures for spin-parity quantum numbers ${J}^{P}={0}^{+}$, ${1}^{+}$, and ${2}^{+}$ and in the 0 and 1 isospin sectors are considered. Possible tightly bound and narrow resonance states are obtained for double-charm and double-bottom tetraquarks with $I{J}^{P}=0{1}^{+}$, and these exotic states are also obtained in charm-bottom tetraquarks with $0{0}^{+}$ and $0{1}^{+}$ quantum numbers. Only a loosely bound state is found in charm-bottom tetraquarks of $0{2}^{+}$ states. All of these bound states within meson-meson configurations are loosely bound whether in color-singlet channels or coupling to hidden-color ones. However, compact structures are available in diquark-antidiquark channels except for charm-bottom tetraquarks in $0{2}^{+}$ states.