Bound states of multi-nucleon channels in N_f=2+1 lattice QCD

We calculate the energies for multi-nucleon ground states with the nuclear mass number less than or equal to 4 in 2+1 flavor QCD at the lattice spacing of a = 0.09 fm employing a relatively heavy quark mass corresponding to m_pi = 0.51 GeV. We investigate the volume dependence of the energy shift of the ground state and the state of free nucleons to distinguish a bound state from attractive scattering states. From the investigation we conclude that ^4He, ^3He, deuteron and dineutron are bound at m_pi = 0.51 GeV. We compare their binding energies with those in our quenched studies and also with some recent investigations.