arXiv subjects
Publications and source records attributed to M. Oka.
The negative-parity baryons are studied by a novel approach in the QCD sum rule. It is found that the parity of the ground-state nucleon is determined by the sign of the quark condensate. We predict the mass of negative-parity nucleon.
We study the $η\to γγ$ and $η\to π^0 γγ$ decays using an extended three-flavor Nambu-Jona-Lasinio model that includes the 't~Hooft instanton induced interaction. We find that the $η$-meson mass, the $η\to γγ$ decay width and the $η\to π^0 γγ$ decay width are in good agreement with the experimental values when the $U_{A}(1)$ breaking is strong and the flavor $SU(3)$ singlet-octet mixing angle $θ$ is about zero. The effects of the $U_A(1)$ breaking on the baryon number one and two systems are also studied.
We study the $η\to π^0 γγ$ decay via the quark-box diagram in the three-flavor Nambu--Jona-Lasinio model that includes the $U_A (1)$ breaking effect. We find that the $η$-meson mass, the $η\to γγ$ decay width and the $η\to π^0 γγ$ decay width are in good agreement with the experimental values when the $U_A (1)$ breaking is strong and the flavor $SU(3)$ singlet-octet mixing angle $θ$ is about zero. The photon energy and the photon invariant mass spectra in $η\to π^0 γγ$ are compared with those in the chiral perturbation theory.
We study the $η\to 2 γ$ decay using an extended three-flavor Nambu-Jona-Lasinio model that includes the 't~Hooft instanton induced interaction. The $η$ meson mass and the $η\to 2 γ$ decay width are reproduced simultaneously with a rather strong instanton induced interaction. The calculated $η$ decay constant is $f_η= 2.23 f_π$ and it suggests that the $η$ meson is no longer the Goldstone boson.
A charge-symmetry-breaking nucleon-nucleon force due to the up-down quark mass difference is evaluated in the quark cluster model. It is applied to the shell-model calculation for the isovector mass shifts of isospin multiplets and the isospin-mixing matrix elements in 1s0d-shell nuclei. We find that the contribution of the quark mass difference effect is large and agrees with experiment. This contribution may explain the Okamoto-Nolen-Schiffer anomaly, alternatively to the meson-mixing contribution, which is recently predicted to be reduced by the large off-shell correction.
We study the $K \to 2 π$ decays using the $U_L(3) \times U_R(3)$ version of the Nambu-Jona-Lasinio model with the effective $ΔS = 1$ nonleptonic weak interaction. The $ΔI = {3/2}$ amplitude is in reasonable agreement with experimental data. On the other hand, the calculated $ΔI = {1/2}$ amplitudes strongly depend on the mass of the low-lying scalar-isoscalar $σ$ meson, and therefore give a strong constraint on the parameters of the model.
The QCD sum rule is applied to the H dibaryon and is compared to the flavor non-singlet di-nucleon. We find that the H dibaryon is almost degenerate to the di-nucleon in the $SU(3)_{flavor}$ limit and therefore is not deeply bound as far as th\ e threshold parameter is adjusted not to have a di-nucleon bound state. After introducing the $SU(3)_{f}$ breaking effects, the H dibaryon is found to be bound by $40 MeV$ below the $ΛΛ$ threshold.