arXiv subjects
Publications and source records attributed to Tomoyuki Maruyama.
We study the monopole oscillation in the bose-fermi mixed condensed system by performing the time-dependent Gross-Pitaevskii and Vlasov equations. We study the resonant oscillation where the intrinsic frequencies of boson and fermion oscillations are same.
We investigate collective spin excitations in two-component fermion condensates with special consideration of unequal populations of the two components. The frequencies of monopole and dipole modes are calculated using Thomas-Fermi theory and the scaling approximation. We demonstrate that spin oscillations have more sensitivity to the interaction and the properties of the condensates than the density oscillations.
Role of the Landau-Migdal parameters with the pseudovector ($g_a$) and the tensor coupling ($g_t$) is examined for the giant Gamow-Teller (GT) states in the relativistic random phase approximation (RPA). The excitation energy is dominated by both $g_a$ and $g_t$ in a similar way, while the GT strength is independent of $g_a$ and $g_t$ in the RPA of the nucleon space, and is quenched, compared with that in non-relativistic one. The coupling of the particle-hole states with nucleon-antinucleon states is expected to quench the GT strength further through $g_a$.
Using the density functional theory (DFT) with the relativistic mean field (RMF) model, we study the non-uniform state of nuclear matter, ``nuclear pasta''. We self-consistently include the Coulomb interaction together with other interactions. It is found that the Coulomb screening effect is significant for each pasta structure but not for the bulk equation of state (EOS) of the nuclear pasta phase.
Two aspects of quark matter at high density are addressed: one is color superconductivity and the other is ferromagnetism. We are mainly concerned with the latter and its relation to color superconductivity, which we call "color magnetic superconductivity". The relation of ferromagnetism and chiral symmetry restoration is also discussed.
A coexistent phase of spin polarization and color superconductivity in high-density QCD is studied at zero temperature. The axial-vector self-energy stemming from the Fock exchange term of the one-gluon-exchange interaction has a central role to cause spin polarization. As a significant feature, the Fermi surface is deformed by the axial-vector self-energy and then rotation symmetry is spontaneously broken down. The gap function results in being anisotropic in the momentum space in accordance with the deformation. It is found that spin polarization barely conflicts with color superconductivity, and almost coexists with it.
We study the spin-polarization mechanism in the highly dense nuclear matter with the relativistic mean-field approach. In the relativistic Hartree-Fock framework we find that there are two kinds of spin-spin interaction channels, which are the axial-vector and tensor exchange ones. If each interaction is strong and different sign, the system loses the spherical symmetry and holds the spin-polarization in the high-density region. When the axial-vector interaction is negative enough, the system holds ferromagnetism.
We study the excited energy of the isoscalar giant quadrupole resonance with the scaling method in the relativistic many-body framework. In this calculation we introduce the momentum-dependent parts of the Dirac self-energies arising from the one-pion exchange on the assumption of the pseudo-vector coupling with nucleon field. It is shown that this momentum-dependence enhances the Landau mass significantly and thus suppresses the quadrupole resonance energy even giving the small Dirac effective mass which causes a problem in the momentum-independent mean-field theory.
Quantum molecular dynamics is applied to study the ground state properties of nuclear matter at subsaturation densities. Clustering effects are observed as to soften the equation of state at these densities. The structure of nuclear matter at subsaturation density shows some exotic shapes with variation of the density.
We study the photoreaction in the delta energy region using the QMD approach. The proton and pion cross-sections are calculated and compared with experimental data. Through this work we examine the multistep contributions in the cross-sections and the {$π- Δ$} dynamics.
Properties of dense hadronic matter including strange particles are studied within the relativistic mean-field theory (RMFT). The possibility of kaon condensation is reexamined, and a simple condition is found for the parameters included in RMFT.
We simulate the fragmentation processes in the {$α$~$+$~Au~} collisions at a bombarding energy of 5 GeV/u using the simplified RQMD approach plus the statistical decay model. We find from the simulation that the angular-distribution of the intermediate mass fragments has a sideward peak, more strongly in the transverse direction than in the beam-direction, when the intermediate nucleus formed by the dynamical process has an annular eclipse shape, which explains the experimental results.
The production cross sections of various fragments from proton-induced reactions on $^{56}$Fe and $^{27}$Al have been analyzed by the Quantum Molecular Dynamics (QMD) plus Statistical Decay Model (SDM). It was found that the mass and charge distributions calculated with and without the statistical decay have very different shapes. These results also depend strongly on the impact parameter, showing an importance of the dynamical treatment as realized by the QMD approach. The calculated results were compared with experimental data in the energy region from 50 MeV to 5 GeV. The QMD+SDM calculation could reproduce the production cross sections of the light clusters and intermediate-mass to heavy fragments in a good accuracy. The production cross section of $^{7}$Be was, however, underpredicted by approximately 2 orders of magnitude, showing the necessity of another reaction mechanism not taken into account in the present model.
Intermediate mass fragment (IMF) multiplicity has been investigated for Au+Au reactions at incident energies of 100, 250 and 400 MeV/A. From the analysis of the impact-parameter-dependence of the IMF multiplicity using our QMD plus statistical evaporation model, we found that 1) statistical decay process modifies the results greatly, and 2) the Fermi motion plays a role to increase the IMF multiplicity for whole impact-parameter range.
In order to investigate relativistic effects we compare the transverse flow calculated by using the four versions of the QMD approaches with that of the full covariant RQMD approach. From the comparison we conclude that the simplified RQMD (RQMD/S), which uses the common time coordinate to all particles, can be used instead of RQMD up to 6 GeV/u.
We define the Dirac-Fock current to hold the current conservation in the momentum-dependent Dirac fields, and discuss its effect on the magnetic-moment in the nuclear matter. It is shown that the Dirac-Fock current can largely reduce the magnetic-moment even in the isovector case, whose value has been too big due to the small effective mass in the usual relativistic Hartree approximation.
The preequilibrium (nucleon-in, nucleon-out) angular distributions of $^{27}$Al, $^{58}$Ni and $^{90}$Zr have been analyzed in the energy region from 90 to 200 MeV in terms of the Quantum Moleculear Dynamics (QMD) theory. First, we show that the present approach can reproduce the measured (p,xp') and (p,xn) angular distributions leading to continuous final states without adjusing any parameters. Second, we show the results of the detailed study of the preequilibrium reaction processes; the step-wise contribution to the angular distribution, comparison with the quantum-mechanical Feshbach-Kerman-Koonin theory, the effects of momentum distribution and surface refraction/reflection to the quasifree scattering. Finally, the present method was used to assess the importance of multiple preequilibrium particle emission as a function of projectile energy up to 1 GeV.
We simulate the fragmentation processes in the \CaCa collisions at the bombarding energy 1.05 GeV/u using the Lorentz covariant RQMD and the non-covariant QMD approaches, incorporated with the statistical decay model. By comparing the results of RQMD with those of QMD, we examine the relativistic effects and find that the multiplicity of the $α$ particle after the statistical decay process is sensitive to the relativistic effects. It is shown that the Lorentz covariant approach is necessary to analyze the fragmentation process even at the energy around \Elab = 1 GeV/u as long as we are concerned with the final observables of the mass distribution, particularly, the light fragments around $A = 3 \sim 4$.