On the basis of the Brueckner-Hartree-Fock method with the nucleon-nucleon forces obtained from lattice QCD simulations, the properties of the medium-heavy doubly-magic nuclei such as 16^O and 40^Ca are investigated. We found that those nuclei are bo
und for the pseudo-scalar meson mass M_PS ~ 470 MeV. The mass number dependence of the binding energies, single-particle spectra and density distributions are qualitatively consistent with those expected from empirical data at the physical point, although these hypothetical nuclei at heavy quark mass have smaller binding energies than the real nuclei.
Charmed tetraquarks $T_{cc}=(ccbar{u}bar{d})$ and $T_{cs}=(csbar{u}bar{d})$ are studied through the S-wave meson-meson interactions, $D$-$D$, $bar{K}$-$D$, $D$-$D^{*}$ and $bar{K}$-$D^{*}$, on the basis of the (2+1)-flavor lattice QCD simulations wit
h the pion mass $m_{pi} simeq $410, 570 and 700 MeV. For the charm quark, the relativistic heavy quark action is employed to treat its dynamics on the lattice. Using the HAL QCD method, we extract the S-wave potentials in lattice QCD simulations, from which the meson-meson scattering phase shifts are calculated. The phase shifts in the isospin triplet ($I$=1) channels indicate repulsive interactions, while those in the $I=0$ channels suggest attraction, growing as $m_{pi}$ decreases. This is particularly prominent in the $T_{cc} (J^P=1^+,I=0)$ channel, though neither bound state nor resonance are found in the range $m_{pi} =410-700$ MeV. We make a qualitative comparison of our results with the phenomenological diquark picture.
