Narrow Results

We study the effect of the tensor correlation using a mean-field-type model and a shell model. To treat the tensor correlation in a mean-field-type model, we introduce single-particle states with the parity and charge mixing considering the pseudoscalar and isovector characters of the pion, which mediates the tensor force. We study closed-shell and sub-closed-shell oxygen isotopes and find that a sizable attractive energy from the tensor force is obtained by introducing the parity and charge mixing. We also perform a shell model calculation up to two-particle–two-hole configurations. A large attraction energy is obtained for ¹⁶O when we introduce single-particle wave functions with narrow widths.

Quenched lattice QCD results of nuclear forces are presented. Inter-nucleon potentials are constructed from Bethe-Salpeter wave functions of two nucleon states by using a Schrödinger-type equation. The results of the central force in ¹S₀ channel posses the repulsive core at short distance as well as the attraction at medium distance, both of which are enhanced in the light quark mass region. A preliminary result on the tensor force is also presented with the central force in ³S₁ channel.

We study the effect of the tensor force on nuclear structure with mean-field and beyond-mean-field methods. An important correlation induced by the tensor force is two-particle–two-hole (2p2h) correlation, which cannot be treated with a usual mean-field method. To treat the 2p2h tensor correlation, we develop a new framework (charge- and parity-projected Hartree-Fock (CPPHF) method), which is a beyond-mean-field method. We apply the CPPHF method to oxygen isotopes including neutron-rich ones. The potential energy from the tensor force has the same order of magnitude as that from the LS force and becomes smaller with neutron number, which indicates that excess neutrons do not contribute to the 2p2h tensor correlation significantly. We also study the effect of the tensor force on spin-orbit-splitting (ls-splitting) in a neutron-rich fluorine isotope ²³F. The tensor force reduces the ls-splitting for the proton d-orbits by about 3MeV. This effect is important to reproduce the experimental value.

Gamow–Teller states, possibly with narrow widths, have been searched for by the ⁴He(³He, t) reaction with an energy resolution of 100 keV. The search is motivated by theoretical discussions on the role of pions in nuclear structure and simulation of supernovae explosion. In the preliminary analysis of the spectrum at around 0°, no significant narrow structure is observed.

One of the methods to obtain a precise solution of a few-body equation is to expand the orbital part of the wave function into the correlated Gaussian with double global vectors. In this contribution, we report our recent studies applying this method to light nuclei, (i) excited states of ⁴He and (ii) two-nucleon momentum distribution in ⁶He and ⁶Li, especially focusing on the importance of the tensor force.

β-decay half-lives around ⁷⁸Ni and ¹³²Sn are studied with proton-neutron Quasiparticle Random Phase Approximation on the basis of Skyrme-Hartree-Fock (SHF) method. We take into account tensor force correlation in calculating the ground and excited states and find it improves the half-life of ¹³²Sn. However, the Q value is still underestimated. We also discuss that half-lives do not strongly depend on type of particle-particle interaction in isospin T = 0 channel.

In this work, effects of tensor force on the evaluation of shell structure of Z = 28 and Z = 82 isotopes are investigated in the framework of Hartree–Fock+BCS approach. Skyrme type SLy5 and SIII interactions are used with and without tensor interaction. The effect of tensor force on the gap evaluation, single particle energies and spin-orbit splittings of the selected isotopic chain are presented. Pairing energy results are also discussed. It is shown that tensor force plays a crucial role in the evaluation of the single particle states and changing spin-orbit splittings of Nickel and Lead isotopic chain.