Double-heavy tetraquarks

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 (QQq̄q̄, $Q=c$, 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 JP=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 IJP=01⁺, and these exotic states are also obtained in charm-bottom tetraquarks with 00⁺ and 01⁺ quantum numbers. Only a loosely bound state is found in charm-bottom tetraquarks of 02⁺ 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 02⁺ states.