The tetraquark candidate Z_c (3900) from dynamical lattice QCD simulations

The structure of the tetraquark candidate Z_c (3900), which has been experimentally reported in e⁺e_- collisions, is studied by s-wave meson-meson coupled-channel scattering on the lattice. The s-wave interactions among the πJ/φ, ρη_c and DD̄^∗ channels are derived from (2 + 1)-flavor dynamical QCD simulations at mπ = 410-700MeV. It is found that the interactions are dominated by the off-diagonal πJ/φ-DD̄^z.ast; and ρη_c-DD̄^z.ast; couplings. With the interactions obtained, the s-wave two-body amplitudes and the pole position in πJ/φ-ρη_c-DD̄^z.ast; coupled-channel scattering are calculated. The results show that Z_c (3900) is not a conventional resonance but a threshold cusp. A semiphenomenological analysis with the coupled-channel interaction to the experimentally observed decay mode is also presented to confirm the conclusion.