Ken-ichi Makino

PION CONDENSATION BASED ON A RELATIVISTIC DESCRIPTION OF PARTICLE-HOLE AND DELTA-HOLE EXCITATIONS

The critical density of neutral pion condensation is reinvestigated based on the relativistic framework and compared with nonrelativistic results. The particle-hole and delta-hole polarizations of the pion selfenergy are calculated in the relativistic way by using a new set of Landau–Migdal parameters derived from recent experimental data. It is concluded that the use of relativistic particle-hole and delta-hole excitations for the pion selfenergy increases the critical density, but still leads to condensation for densities from two to three times the normal nuclear matter density within the random phase approximation.

EFFECTIVE MESON MASSES, EFFECTIVE MESON–NUCLEON COUPLINGS AND NEUTRON STAR RADII

Using a generalized mean field theory, we have studied relations among effective meson masses, effective meson–nucleon couplings and equations of state (EOS) in asymmetric nuclear matter. If the effective ω-meson mass becomes smaller at high density, the EOS becomes stiffer. However, if we require that the ω-meson mean field is proportional to baryon density, the effective ω–nucleon coupling also becomes smaller at the same time as the effective ω-meson mass becomes smaller. Consequently, the EOS becomes softer. A similar relation is found for the effective ρ-meson mass and the effective ρ–nucleon coupling. We have also studied relations among effective meson masses, effective meson–nucleon couplings and a radius R of a neutron star. R depends somewhat on the value of the effective ω-meson mass and the effective ω–nucleon coupling.

VERTEX CORRECTIONS IN THE NUCLEAR SCHWINGER–DYSON FORMALISM

We develop the Nuclear Schwinger–Dyson (NSD) formalism to include the effects of ladder diagrams by modifying the vertex. In this extension, the NSD equation sums up both ring diagrams and ladder diagrams self-consistently. The results are compared with mean field theory, Hartree Fock and bare-vertex NSD calculations. It is shown that the vertex correction is important from the following viewpoints. First, the vertex correction greatly modifies the meson propagators, and we can avoid the ghost-pole from meson propagators in a self-consistent way. Secondly, it gives a large negative correlation-energy compared with the other calculations; as a result, it gives a softer equation of state which is preferable according to the experimental data.

MOLECULAR DYNAMIC SIMULATIONS OF HYDROGEN STORING IN CLATHRATE HYDRATES

The stability of hydrogen clathrate hydrate was investigated using a classical Molecular Dynamic (MD) calculation code “MXDTRICL” as a theoretical approach. Arranging hydrogen molecules one by one into host-frame of the hydrogen hydrates, the inclusion energy of their system was evaluated, where Lennard-Jones potential and two types of TIP4P potentials were adopted on the MD calculations as intermolecular potentials. From the result, it is concluded that multiple molecules are included in both large and small cages so that the storage density could attain higher than 6wt% for any potential. Observation of the movement of H2 molecules in the cage under various conditions revealed that H2 molecules are not stable in the cage and a few part of the H2 molecules come in and go out of the cage through the center hole between hexagons.

EFFECTIVE MESON MASS IN NUCLEAR MATTER BASED ON DISPERSION EQUATION INCLUDING

Effective meson masses of σ, ω, ρ and π in nuclear matter are calculated from the meson self-energy of the particle–antiparticle excitations. Instead of the traditional renormalization, the dispersion relation method is used to calculate the real part from the finite imaginary part, since the tensor coupling of the pion and ρ meson is not renormalized in the usual sense. In this paper, we show the effects from antidelta-nucleon and delta-antinucleon excitations in π meson mass beside nucleon–antinucleon excitation. It is also shown that agreement is obtained on the ω meson mass predicted by the subtraction method and ρ meson mass by the QCD sum rule method. It is concluded that the dispersion equation method leads to the fact that all the meson mass decreases as the baryon density increases, and it supports the chiral symmetry restoration.

{\rm N} \bar{\rm N},\ \Delta \bar{\rm N},\ \bar\Delta {\rm N}

The critical density of neutral pion condensation is investigated based on the relativistic framework and compared with nonrelativistic results. The particlehole and delta-hole polarizations of the pion selfenergy are calculated in the relativistic way by using a new set of Landau-Migdal parameters derived from a recent experimental data. It is concluded that the use of relativistic particle-holeand delta-holeexcitations for the pion selfenergy increases the critical density compared with the non-relativistic result, however still leads to condensation for densities from 2 to 4 times normal nuclear matter density.