We investigate the formation of light nuclei with the nuclear mass number less than or equal to four in $2+1$ flavor QCD using a nonperturbative improved Wilson quark and Iwasaki gauge actions. The quark mass is decreased from our previous work to the one corresponding to the pion mass of 0.30 GeV. In each multinucleon channel, the energy shift of the ground state relative to the assembly of free nucleons is calculated on two volumes, whose spatial extents are 4.3 and 5.8 fm. From the volume dependence of the energy shift, we distinguish a bound state of multinucleons from an attractive scattering state. We find that all the ground states measured in this calculation are bound states. As in the previous studies at larger $m_{\pi }$, our result indicates that at $m_{\pi }=0.30\mathrm{GeV}$ the effective interaction between nucleons in the light nuclei is relatively stronger than the one in nature, since the results for the binding energies are larger than the experimental values and a bound state appears in the dineutron channel, which is not observed in experiment. Possible sources of systematic error in this calculation are discussed.

• Received 14 February 2015

DOI:https://doi.org/10.1103/PhysRevD.92.014501