Near-threshold states in coupled DD^-D^D^ scattering from lattice QCD

The first determination of doubly-charmed isospin-0 coupled-channel DD^-D^ D^ scattering amplitudes from lattice QCD is presented. The finite-volume spectrum is computed for three lattice volumes with a light-quark mass corresponding to m_ 391 MeV and is used to extract the scattering amplitudes in JP = 1^+ via the L\"uscher quantization condition. By analytically continuing the scattering amplitudes to complex energies, a T₂₂ pole corresponding to a virtual bound state is found below DD^ threshold. We also find a second pole, T₂₂^, corresponding to a resonance pole below the kinematically closed D^ D^ channel, to which it has a strong coupling. A non-zero coupling is robustly found between the S-wave D D^ and D^ D^ channels producing a clear cusp in the D D^ amplitude at the D^ D^ threshold energy. This suggests that the experimental T₂₂^ should be observable in D D^ and D^ D^ final states at ongoing experiments.