| Research Abstract |
Between April 2001 and March 2003, the following research results have been obtained :
1) Quark correlations in the nucleon and structure function of the nucleon (Ref.No.1) : Treating the nucleon as a relativistic 3-quark bound state, we studied the interactions (correlations) between the quarks By taking into account the scalar diquark and axial vector diquark channels, we constructed the wave function of the nucleon. Besides this, also the effects of the meson cloud were considered in order to calculate the static properties of the nucleon (magnetic moments, expectation value of the spin, nucleon-meson coupling constants, etc) and the structure function of the nucleon. From the study of these physical quantities, we could obtain information on the probabilities of the above mentioned diquark channels and the pionic channel.
2) Equations of state of nuclear matter and quark matter (Ref.No.2,3) : By making use of the mean field approximation for the many -body system, we constructed the
… More
nuclear matter equation of state which takes into account the internal structure of the single nucleon as described above. It has been well known that in effective theories based on the linear realization of chiral symmetry, like the Nambu-Jona-Lasinio model, one cannot reproduce the saturation properties of nuclear mattet However, by taking into account also the effects of confinement in a phenomenological way, in this research we succeeded to describe a stable many body state. Furthermore, in order to study the behavior of matter at high densities, we also constructed the quark matter equation of state, and investigated the conditions which can lead to a phase transition from nuclear matter to quark matter. We found that the phase transition leads to a color superconducting quark matter state, and we pointed out the strong effect of quark pairing on the transition density.
3) Nuclear structure functions and the EMC Effect (Ref.No.4,5) : By combining the above descriptions of the single nucleon and the nuclear matter equation of state, we investigated the structure function of a nucleon bound in the nuclear medium. By studying the medium effects on the structure function in detail, we found that the mean vector potential plays a very important role. Namely, because of the mean vector potential the quark momentum distribution in a bound nucleon becomes narrow, and for Bjorken x>0.3 the nucleon structure function becomes suppressed compared to the case of a free nucleon. In this way we could explain the experimentally observed EMC effect. We also confirmed the validity of the number and momentum sum rules in this framework.
4) Sum rules in nuclei (Ref.No.6) : Finally, we also studied the Gamow-Teller sum rule and the electric dipole (El) sum rule in nuclei. Less
|
