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Lattice study of nuclear forces

Recent progress of lattice QCD study of nuclear forces (potentials) is reviewed. Scattering phase shift is an important observable for two particle system. In lattice QCD, phase shifts are calculated from long distance behavior of Bethe-Salpeter (BS) wave functions by Luescher's finite volume method. For applications to nuclear physics of multi-nucleon system, it is more advantageous to convert the information of phase shifts in the form of potentials. We therefore extend the method so as to generate the potentials from BS wave functions. These potentials are faithful to scattering phase shift by construction, because they can reproduce BS wave functions in which the information of phase shift is embeded in the long distance part.The method was first applied to the central potential in NN system. It is now applied to many objects, such as tensor potential, hyperon potentials, energy dependence of nuclear potentials, and investigations of the repulsive core at short distance.