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 (QQ (q) over bar(q) over bar, 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 IJ(P) = 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.