Incorporating DDπ effects and left-hand cuts in lattice QCD studies of the T_cc(3875)^+

We generalize the relativistic field-theoretic three-particle finite-volume scattering formalism to describe generic DDπ systems in the charm C=2 sector. This includes the isospin-0 channel, in which the recently discovered doubly-charmed tetraquark T_cc(3875)^+ is expected to manifest as a pole in the DD π→ DD π scattering amplitude. The formalism presented here can also be applied to lattice QCD settings in which the D^* is bound and, in particular, remains valid below the left-hand cut in D D^* scattering, thus resolving an issue in previous analyses of lattice-determined finite-volume energies.