arXiv subjects

Sachiko Takeuchi

Publications and source records attributed to Sachiko Takeuchi.

34 records · Page 2Linked to original sources

arXiv2005

P-wave Pentaquark and its Decay in the Quark Model with Instanton Induced Interaction

P-wave pentaquarks with strangeness +1, I=0 and J^P=1/2^+ are studied in the non-relativistic quark model with instanton induced interaction (III). We present their mass splittings and orbital-spin-isospin-color structures. It is found that decompositions of the wave functions are sensitive to III, while the mass splittings are insensitive. The decay of the lowest energy pentaquark, Θ^+, is found to be suppressed when the contribution of III is increased. Its wave function is dominated by Jaffe-Wilczek-type configuration at large III.

hep-ph↗

arXiv2004

Pentaquark as a NK^* bound state with TJ^P=0{3/2}^-

We have investigated negative-parity uudd\bar{s} pentaquarks by employing a quark model with the meson exchange and the effective gluon exchange as qq and q\bar{q} interactions. The system for the five quarks is dynamically solved; the effects of qq and q\bar{q} correlations on the wave function are taken into account. It is found that the masses of the pentaquarks are reasonably low. The lowest-mass state is found to be TJ^P=0{1/2}^-, and the next lowest one is 0{3/2}^-. The former is reported to have a large width. We argue the observed narrow peak corresponds to the latter state. It is still necessary to introduce an extra attraction to reduce the mass further by 140 -- 280 MeV to reproduce the observed Θ^+ mass. Since their level splitting is found to be less than 80 MeV, the lower level will not become a bound state below the NK threshold even after such an attraction is introduced. It is also found that the relative distance of two quarks with the attractive interaction is found to be by about 1.2 -- 1.3 times closer than that of the repulsive one. The two-body correlation seems important in the pentaquark systems.

hep-ph↗

arXiv2004

Pentaquark with diquark correlations in a quark model

We have investigated uudd\sbar pentaquarks by employing quark models with the meson exchange and the effective gluon exchange as qq and q\qbar interactions. The system for five quarks is dynamically solved; two quarks are allowed to have a diquark-like qq correlation. It is found that the lowest mass of the pentaquark is about 1947 -- 2144 MeV. There are parameter sets where the mass of the lowest positive-parity state become lower than that of the negative-parity states. Which parity corresponds to the observed peak is still an open question. Relative distance of two quarks with the attractive interaction is found to be by about 1.2 -- 1.3 times closer than that of the repulsive one. The diquark-like quark correlation seems to play an important role in the pentaquark systems.

hep-ph↗

arXiv2004

Contribution of Instanton Induced Interaction for Penta-quarks in MIT Bag Model

Roles of instanton induced interactions (III) in the masses of pentaquark baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed using the MIT bag model. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of pairs in multi-quark systems. In contrast, the three-body $u$-$d$-$s$ interaction is repulsive. It is found that III lowers the mass of negative-parity Theta^+ as much as 100 MeV from the mass predicted by the bag model without III.

hep-ph↗

arXiv2004

Effects of Instanton Induced Interaction on the Pentaquarks

Roles of instanton induced interactions (III) in the masses of pentaquark baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed using the MIT bag model in the negative parity case. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of pairs in multi-quark systems. In contrast, the three-body u-d-s interaction is repulsive. It is found that III lowers the mass of Theta^+ as much as 100 MeV from the mass predicted by the bag model without III.

hep-ph↗

arXiv2003

A quark model analysis of the charge symmetry breaking in nuclear force

In order to investigate the charge symmetry breaking (CSB) in the short range part of the nuclear force, we calculate the difference of the masses of the neutron and the proton, $Δ{\rm M}$, the difference of the scattering lengths of the p-p and n-n scatterings, $Δa$, and the difference of the analyzing power of the proton and the neutron in the n-p scattering, $ΔA(θ)$, by a quark model. In the present model the sources of CSB are the mass difference of the up and down quarks and the electromagnetic interaction. We investigate how much each of them contributes to $Δ{\rm M}$, $Δa$ and $ΔA(θ)$. It is found that the contribution of CSB of the short range part in the nuclear force is large enough to explain the observed $ΔA(θ)$, while $Δa$ is rather underestimated.

nucl-th↗

arXiv2002

Pauli-blocking Effect in a Quark Model

Pauli-Blocking effect on the kinetic term is investigated by employing the quark cluster model. The effect can be understood by the change of the degrees of the mixing between the incoming wave and the 0$\ell$ state of the inter-cluster wave function, which can be expressed by a potential which is highly nonlocal. We look into the properties of this effect by comparing equivalent local potentials. In the channel where the Pauli-blocking effect is small, the on-shell equivalent local potential simulates the nonlocal potential well even for the off-shell behavior. On the other hand, the off-shell behavior is very different from the original one where the effect is large. This off-shell behavior, however, can well be simulated by considering the nonlocal matrix elements only between the $0s$ state and the other states. The energy dependent potentials are also constructed and found to be helpful to understand the energy dependence of the effect.

hep-ph↗

arXiv2002

Quark Model and Equivalent Local Potential

In this paper, we investigate the short-range repulsion given by the quark cluster model employing an inverse scattering problem. We find that the local potential which reproduces the same phase shifts to those given by the quark cluster model has a strong repulsion at short distances in the NN1s0 channel. There, however, appears an attractive pocket at very short distances due to a rather weak repulsive behavior at very high energy region. This repulsion-attractive-pocket structure becomes more manifest in the channel which has an almost forbidden state, SigmaN(T=3/2)3s1. In order to see what kinds of effects are important to reproduce the short-range repulsion in the quark cluster model, we investigate the contribution coming from the one-gluon-exchange potential and the normalization separately. It is clarified that the gluon exchange constructs the short-range repulsion in the NN1s0 while the quark Pauli-blocking effect governs the feature of the repulsive behavior in the SigmaN(T=3/2)3s1 channel.

hep-ph↗

arXiv2000

Effects of $Σ$N channels on the Spin-Orbit Force in $Λ$-hypernuclei

Effects of the $Σ$N channels on the spin-orbit force in $Λ$-hypernuclei are investigated. It is found that the cancellation between the symmetric and the antisymmetric $Λ$N spin-orbit force becomes more complete when the contribution from the $Σ$N channels is included. This may be the one of the reasons why the observed LS splitting of the $Λ$ single particle energy is very small.

hep-ph↗

arXiv2000

Effects of Instantons on the YN Interaction

We investigate the symmetric and anti-symmetric spin-orbit forces (SLS and ALS) of the effective $Λ$N interaction derived from a quark cluster model with the instanton-induced interaction (\III), which can reproduce the observed YN cross sections as well as the observed NN scattering data. It is found that coupling to the $Σ$N channel enhances $Λ$N ALS, and therefore that the cancellation between SLS and ALS in the $Λ$N channel becomes more complete. This may be one of the major reasons why the single-particle spin-orbit force of $Λ$ in nuclei is weak.

hep-ph↗

arXiv1998

Symmetric and Antisymmetric Spin-Orbit Forces in YN Interaction by a Quark Model

The symmetric and antisymmetric spin-orbit forces (SLS and ALS) in the YN interaction are investigated for relative P-wave systems by a valence quark model with the instanton-induced interaction (III). The size of the adiabatic potential at the zero range is shown for each of the YN channels. The nonlocal RGM potential of the LS and ALS forces are also shown for typical YN channels. The size of ALS is comparable to SLS. The channel dependence of ALS, which is determined by the flavor SU(3) symmetry when the one-gluon exchange (OGE) and/or the meson exchange interaction are used, deviates after introducing III. In most of the two-baryon channels, including the two-nucleon channel, the spin-orbit force of the YN interaction is strong. A few exceptional channels, however, are found where III and OGE are canceled to each other, and the spin-orbit force becomes small.

hep-ph↗

arXiv1998

Spin-Orbit Force of Instanton-Induced Interaction in Strange and Charmed Systems

Effects of the spin orbit-force on hadronic systems with strangeness or charm are investigated by a valence quark model with the instanton-induced interaction. By introducing this interaction, the spin-orbit splittings in the negative-parity hyperons becomes 0.14 -- 0.37 times smaller. The flavor-octet baryon mass spectrum and the splittings in the charmed baryons become consistent with the experiments. Though the splitting is also reduced in the flavor-singlet baryons, it still gives two third of the experimental value. The reduction comes from the cancellation between the one-gluon exchange and the instanton-induced interaction, which is channel-specific. In most of the two-baryon channels, the symmetric and antisymmetric spin-orbit force of the YN interaction remains strong after introducing this instanton effect. A few exceptional channels, however, are found where the cancellation affects strongly and the spin-orbit force becomes small.

hep-ph↗

arXiv1995

Effects of Instantons on the Excited Baryons and Two-Nucleon Systems

The effects of the spin-orbit and the tensor parts of the instanton-induced interaction on the excited nonstrange baryons up to $N$=2 and on the two-nucleon systems are investigated. The spin-orbit force from the instanton-induced interaction cancels most of that from the one-gluon exchange in the excited baryons while the spin-orbit force in the nucleon systems remains strong after the inclusion of the instanton-induced interaction. The model including the spin-orbit and the tensor terms of the instanton-induced interaction as well as the one-gluon exchange is found to reproduce successfully the excited baryon mass spectrum and the scattering phase shifts of two nucleons in the spin-triplet relative $P$-wave state.

nucl-th↗

arXiv1995

Direct quark transition potential for $ΛN \to NN$ decay

The weak $ΛN\to NN$ transition is studied in the valence quark model approach. The quark component of the two baryon system is described in the quark cluster model and the weak transition potential is calculated by evaluating the matrix elements of the $ΔS=1$ effective weak Hamiltonian. The transition potential is applied to the decay of hypernuclei and the results are compared with available experimental data. The results indicate that direct quark process is significant and qualitatively different when compared with those in conventional meson-exchange calculations. The direct quark mechanism predicts the violation of the $ΔI = 1/2$ rule for this transition.

hep-ph↗

arXiv1993

Short-range YN interactions in the Quark Cluster Model

A phenomenological model for the hyperon-nucleon interactions is constructed by using the quark cluster model approach to the short-distance baryon-baryon interactions. The model contains the SU(3) symmetric meson exchange interaction at large distances and the quark-exchange short-distance interaction. The main feature of the model is that strong channel dependences of the short range repulsions due to the quark model symmetry. It is pointed out that two channels, ($I$, $S$)= (1/2, 0) and (3/2, 1), of the S-wave sigma-nucleon interactions have extremely strong repulsions at short-distances.

hep-ph↗

arXiv1993

Weak $\Lam N\to NN$ Transition in the Direct Quark Mechanism

The weak $\Lam N\to NN$ transition is studied in the valence quark model approach. The momentum transfer for this transition is so large that the short-distance two baryon dynamics must be taken into account. The two baryon system is described in the quark cluster model and the weak transition amplitude is calculated by evaluating the matrix elements of the effective weak $ΔS= 1$ hamiltonian. The results indicate some qualitative differences when compared with those in conventional meson-exchange calculations. Especially, we conclude that contributions of the $ΔI={3\over2}$ transition are significant and that the discrepancy in the $n-p$ ratio between theory and experiment could be resolved by including the direct-quark processes.

hep-ph↗