DK/Dπ scattering and an exotic virtual bound state at the SU(3) flavour symmetric point from lattice QCD

Elastic S-wave scattering of a charm meson with a light pseudoscalar meson in J^P = 0⁺ is investigated in the flavour \( \overline{\textbf{3}} \), 6 and \( \overline{\textbf{15}} \) sectors at the SU(3)_f flavour point using lattice QCD, working on three volumes with m_π ≈ 700 MeV. Large bases of interpolating operators are employed to extract finite-volume spectra, which are subsequently used with the Lüscher method to provide constraints on infinite-volume scattering amplitudes. Examining the singularities of the amplitudes, the S-wave amplitude in the flavour \( \overline{\textbf{3}} \) sector is found to contain a deeply bound state, strongly coupled to elastic threshold, corresponding to the \( {J}^P={0}^{+}\ {D}_{s0}^{\ast }(2317) \). In the exotic flavour 6 sector a virtual bound state is found at \( \sqrt{s_{\textrm{pole}}} \) = 2510 – 2610 MeV, roughly 40 – 140 MeV below threshold, whereas the \( \overline{\textbf{15}} \) channel shows weak repulsion.