Yoshihiko Kondo

K- pp bound states from Skyrmions

The bound kaon approach to the strangeness in the Skyrme model is applied to investigating the possibility of deeply bound K{sup -}pp states. We describe the K{sup -}pp system as two Skyrmion, around which a kaon field fluctuates. Each Skyrmion is rotated in the space of SU(2) collective coordinate. The rotational motions are quantized to be projected onto the spin-singlet proton-proton state. We derive the equation of motion for the kaon in the background field of two Skyrmions at fixed positions. From the numerical solution of the equation of motion, it is found that the energy of K{sup -} can be considerably small and that the distribution of K{sup -} shows molecular nature of the K{sup -}pp system. For this deep binding, the Wess-Zumino-Witten term plays an important role. The total energy of the K{sup -}pp system is estimated in the Born-Oppenheimer approximation. The binding energy of the K{sup -}pp state is B.E. {approx_equal}126 MeV. The mean square radius of the pp subsystem is {radical}( ){approx_equal}1.6 fm.

Meson baryon couplings from QCD sum rules

Coupling constants of the pseudoscalar mesons to the octet baryons are calculated in the QCD sum rule approach. Two-point correlation function of the baryons are evaluated in a single meson state and the vacuum, which yields the designated coupling. The emphasis is on the flavor SU(3) structure of the coupling constants and reliability in extracting the coupling constants from the two-point correlation functions. We first calculate the baryon-diagonal couplings and study the reliability of the sum rule. The F/D ratio of the coupling is determined in the SU(3) limit. We further formulate the baryon-off-diagonal couplings using the projected correlation functions and the vertex functions, so that the unwanted excited states do not contaminate the sum rule. As an example, the πΛΣ coupling constant is calculated and the flavor SU(3) breaking effect is studied. We find that the effect of SU(3) breaking on the πΛΣ coupling constant is small.

Coupled QCD sum rules for positive and negative-parity nucleons

Abstract A new approach of the QCD sum rule is proposed in which positive and negative-parity baryons couple with each other. With positive and negative-parity states explicitly taken into account, sum rules are derived by means of the dispersion relation in energy. The method is applied to the nucleon channel and the parity splitting of the nucleon resonance states is studied. It is found that the obtained sum rules have a very good Borel stability. This suggests that the ansatz for the spectral function in the present sum rule approximates the physical spectrum better than the usual lowest pole plus continuum ansatz. The predicted masses of the positive and negative nucleons reproduce the experimental ones fairly well. Especially, the mass difference is extremely close to the experimental value.

The F/D ratio and Messon-Baryon couplings from QCD sum rules

Abstract Using QCD sum rules, we compute the diagonal meson–baryon couplings, πNN , ηNN , πΞΞ , ηΞΞ , πΣΣ and ηΣΣ , from the baryon–baryon correlation function with a meson: i ∫ d 4 x e i q·x 〈0|TJ B (x) J B (0)|M(p)〉 . The calculations are performed to leading order in p μ by considering the two separate Dirac structures, i γ 5 γ μ p μ and γ 5 σ μν q μ p ν separately. We first improve the previous sum rule calculations on these Dirac structures for the πNN coupling by including three-particle pion wave functions of twist 4 and then extend the formalism to calculate the other couplings, ηNN , πΞΞ , ηΞΞ , πΣΣ and ηΣΣ . In the SU(3) symmetric limit, we identify the terms responsible for the F/D ratio in the OPE by matching the obtained couplings with their SU(3) relations. Depending on the Dirac structure considered, we find different identifications for the F/D ratio. The couplings including the SU(3) breaking effects are also discussed within our approach.

Two-hadron-irreducible QCD sum rule for pentaquark baryon

We point out that naive pentaquark correlations function include two-hadron-reducible contributions, which are given by convolution of baryon and meson correlation functions and have nothing to do with pentaquark. We show that the two-hadron-reducible contributions are large in the operator product expansion of the correlation functions of three existing works on the pentaquark. Therefore, it is dangerous to draw a conclusion from the sum rules using naive pentaquark correlation functions with naive ansatz for the spectral function under the dispersion integral. Instead, we propose to use the two-hadron-irreducible correlation function, which is obtained by subtracting the two-hadron-reducible contribution from the naive correlation function. Taking one of the works as an example we demonstrate how drastically the results can change if we remove the two-hadron-reducible part from the naive correlation function. We obtain the result opposite to the original work for the parity of the pentaquark.

Spin-3/2 pentaquark in the QCD sum rule approach

We study

Model-independent study of the QCD sum rule for theπNNcoupling constant

IJ^P=0{3/2}^\pm

A projected correlation function approach to the πNN coupling constant in QCD sum rules

and

New approach to axial coupling constants in the QCD sum rule

1{3/2}^\pm

Pentaquarks in QCD Sum Rules

pentaquark states with