Search for possible bound T_cc and T_cs on the lattice

Possible bound states of charmed tetraquarks T_cc = (ccud) and T_cs = (csud) are studied through the s-wave meson-meson interactions, D-D, K -D, D-D∗ and K-D∗, in (2+1)-flavor full QCD sim- ulations with the pion mass mπ ≃ 410, 570 and 700 MeV. To treat the charm-quark dynamics properly, the relativistic heavy quark action is employed. Applying the HAL QCD method to the meson-meson systems, we extract the s-wave potentials between two mesons in lattice QCD simulations, from which the meson-meson scattering phase shifts are also calculated. The phase shifts in the isospin triplet (I=1) channels indicate repulsive interactions, while those in the isospin singlet (I = 0) channels suggest attraction, growing as π decreases. This is particularly promi- nent in the T_cc(JP = 1+, I = 0) channel, though neither bound state nor resonance are found in the range π = 410-700 MeV.