Doubly Charmed Tetraquark T_{cc}^{+} from Lattice QCD near Physical Point

The doubly charmed tetraquark T_{cc}^{+} recently discovered by the LHCb Collaboration is studied on the basis of (2+1)-flavor lattice QCD simulations of the D^{*}D system with nearly physical pion mass m_{π}=146  MeV. The interaction of D^{*}D in the isoscalar and S-wave channel, derived from the hadronic spacetime correlation by the HAL QCD method, is attractive for all distances and leads to a near-threshold virtual state with a pole position E_{pole}=-59(_{-99}^{+53})(_{-67}^{+2})  keV and a large scattering length 1/a_{0}=0.05(5)(_{-2}^{+2})  fm^{-1}. The virtual state is shown to evolve into a loosely bound state as m_{π} decreases to its physical value by using a potential modified to m_{π}=135  MeV based on the pion-exchange interaction. Such a potential is found to give a semiquantitative description of the LHCb data on the D^{0}D^{0}π^{+} mass spectrum. Future study is necessary to perform physical-point simulations with the isospin-breaking and open three-body-channel effects taken into account.