We discuss an ongoing first lattice study of the doubly-charmed tetraquark T₂₂^+ (3875) via a three-body approach. We investigate the DD system in the I=0, C=2 sector, where the T₂₂^+ appears as a pole in the JP = 1^+ DD elastic scattering amplitude. The approach automatically incorporates two-body DD^* and three-body DD effects and treats left-hand cuts due to single exchanges. Two CLS ensembles, X252 and X253, with pion mass M_ 280 MeV, are used, and an operator set comprised of two- and three-hadron and tetraquark operators is employed to extract finite-volume energies. Additional inputs are required for the three-body finite-volume analysis, in the form of amplitudes for the I=1 DD and I=1/2 D two-body subsystems. We present preliminary results for these subchannels and perform exploratory three-body spectra determinations for simple choices of the three-particle K-matrix K ₃₅, ₃, allowing a first comparison to the lattice spectrum.
Raposo et al. (Thu,) studied this question.