arXiv subjects

K. Saito

Publications and source records attributed to K. Saito.

104 records · Page 6Linked to original sources

arXiv1998

Quark and gluon condensates in the quark-meson coupling model

Using the quark-meson coupling (QMC) model, we study the density dependence of the quark and gluon condensates in nuclear matter. We show that the change of the quark condensate is mainly driven by the scalar field in the medium and that the reduction of the quark condensate is suppressed at high density, even in the mean-field approximation. The gluon condensate decreases by 4 - 6 % at nuclear saturation density. We also give a simple relationship between the change of the quark condensate and that of a hadron mass in the medium.

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arXiv1997

The quark-meson coupling model for Lambda, Sigma and Xi hypernuclei

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both infinite nuclear matter and finite nuclei, is applied to a systematic study of $Λ, Σ$ and $Ξ$ hypernuclei. Assumptions made in the present study are, (i) the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, and (ii) an SU(6) valence quark model for the bound nucleons and hyperon. The model automatically leads to a very weak spin-orbit interaction for the $Λ$ in a hypernucleus. Effects of the Pauli blocking at the quark level, particularly in the open, coupled, $ΣN - ΛN$ channel (strong conversion), is also taken into account in a phenomenological way.

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arXiv1997

Self-consistent description of $Λ$ hypernuclei in the quark-meson coupling model

The quark-meson coupling (QMC) model, which has been successfully used to describe the properties of both finite nuclei and infinite nuclear matter, is applied to a study of $Λ$ hypernuclei. With the assumption that the (self-consistent) exchanged scalar, and vector, mesons couple only to the u and d quarks, a very weak spin-orbit force in the $Λ$-nucleus interaction is achieved automatically. This is a direct consequence of the SU(6) quark model wave function of the $Λ$ used in the QMC model. Possible implications and extensions of the present investigation are also discussed.

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arXiv1997

In-medium electron-nucleon scattering

In-medium nucleon electromagnetic form factors are calculated in the quark meson coupling model. The form factors are typically found to be suppressed as the density increases. For example, at normal nuclear density and $Q^2 \sim 0.3 { GeV}^2$, the nucleon electric form factors are reduced by approximately 8% while the magnetic form factors are reduced by only 1 - 2%. These variations are consistent with current experimental limits but should be tested by more precise experiments in the near future.

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arXiv1997

Exchange Currents for Hypernuclear Magnetic Moments

The meson(K and $π$) exchange currents for the hypernuclear magnetic moments are calculated using the effective Lagrangian method. The seagull diagram, the mesonic diagram and the $Σ^0$-excitation diagram are considered. The $Λ$-N exchange magnetic moments for the ${}^5_ΛHe$, ${}^6_ΛHe$ and ${}^6_ΛLi$ are calculated employing the harmonic oscillator shell model. It is found that the two-body correction is about -9% of the single particle value for ${}^5_ΛHe$. The $π$ exchange current, induced only in the $Σ^0$-excitation diagram, is found to give dominant contribution for the isovector magnetic moments of hypernuclei with A=6.

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arXiv1997

Naturalness in the quark-meson coupling model

The quark-meson coupling (QMC) model is examined using Georgi's ``naive dimensional analysis''. We argue that the QMC model is quite natural as an effective field theory for nuclei.

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arXiv1997

Rho-meson mass in light nuclei

The quark-meson coupling (QMC) model is applied to a study of the mass of the $ρ$-meson in helium and carbon nuclei. The average mass of a $ρ$-meson formed in $^{3,4}$He and $^{12}$C is expected to be around 730, 690 and 720 MeV, respectively.

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arXiv1996

Variation of hadron masses in finite nuclei

The quark-meson coupling model, based on a mean-field description of non-overlapping nucleon bags bound by the self-consistent exchange of $σ$, $ω$ and $ρ$ mesons, is extended to investigate the change of hadron properties in finite nuclei. Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons and mesons. Using this unified, self-consistent description of both infinite nuclear matter and finite nuclei, we investigate the properties of some closed-shell nuclei, and study the changes in the hadron masses of the non-strange vector mesons, the hyperons and the nucleon in those nuclei. We find a new, simple scaling relation for the changes of the hadron masses, which can be described in terms of the number of non-strange quarks in the hadron and the value of the scalar mean-field in a nucleus.

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arXiv1996

Quarks in Finite Nuclei

We describe the development of a theoretical description of the structure of finite nuclei based on a relativistic quark model of the structure of the bound nucleons which interact through the (self-consistent) exchange of scalar and vector mesons.

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arXiv1996

The role of nucleon structure in finite nuclei

The quark-meson coupling model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of $σ$, $ω$ and $ρ$ mesons, is extended to investigate the properties of finite nuclei. Using the Born-Oppenheimer approximation to describe the interacting quark-meson system, we derive the effective equation of motion for the nucleon, as well as the self-consistent equations for the meson mean fields. The model is first applied to nuclear matter, after which we show some initial results for finite nuclei.

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arXiv1995

Charge Symmetry Violation in Nuclear Physics

The study of charge symmetry violation in nuclear physics is a potentially enormous subject. Through a few topical examples we aim to show that it is not a subject of peripheral interest but rather goes to the heart of our understanding of hadronic systems.

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arXiv1994

Variations of Hadron Masses and Matter Properties in Dense Nuclear Matter

Using a self-consistent quark model for nuclear matter we investigate variations of the masses of the non-strange vector mesons, the hyperons and the nucleon in dense nuclear matter (up to four times the normal nuclear density). We find that the changes in the hadron masses can be described in terms of the value of the scalar mean-field in matter. The model is then used to calculate the density dependence of the quark condensate in-medium, which turns out to be well approximated by a linear function of the nuclear density. Some relations among the hadron properties and the in-medium quark condensate are discussed.

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arXiv1994

The Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter

The quark-meson coupling model which we have developed previously is extended to incorporate the $δ$ meson. It is then used to study the Nolen-Schiffer anomaly and isospin symmetry breaking in nuclear matter. We find that, in combination with the {\it u-d\/} mass difference, the difference between quark scalar densities in protons and neutrons generates an effective neutron-proton mass difference of the right magnitude. Finally we find that isospin symmetry breaking in the quark condensates can be directly related to the $δ$ meson field.

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arXiv1994

A quark-meson model for nuclear and neutron matter

An explicit quark model, based on a mean field description of non-overlapping nucleon bags bound by the self-consistent exchange of $σ$, $ω$ and $ρ$ mesons, is used to investigate the properties of both nuclear and neutron matter. We establish a clear understanding of the relationship between this model, which incorporates the internal structure of the nucleon, and QHD. Finally, we use the model to study the density dependence of the quark condensate in-medium.

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