The possible exotic meson Zc(3900), found in e+e- reactions, is studied by the method of coupled-channel scattering in lattice QCD. The interactions among πJ/ψ, ρηc, and D-D∗ channels are derived from (2+1)-flavor QCD simulations at mπ=410-700 MeV. The interactions are dominated by the off-diagonal πJ/ψ-D-D∗ and ρηc-D-D∗ couplings, which indicates that the Zc(3900) is not a usual resonance but a threshold cusp. Semiphenomenological analyses with the coupled-channel interaction are also presented to confirm this conclusion.
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