arXiv subjects
Publications and source records attributed to S. Muroya.
After presenting the motivations to explore the low-lying scalar mesons such as the $σ$, $a_0$ and $κ$ in the unquenched as well as quenched lattice QCD, we review the works done by our collaboration (SCALAR Collaboration) with a what-to-do-next list. We briefly mention the imporatance to explore the $N_c$ dependence of and possible effects of the $U_A(1)$ anomaly to the properties the low-lying scalar mesons.
Using lattice QCD with dynamical Wilson fermions, we study I=0 and $J^{P}=0^{+}$ channel which is constructed by $\frac{1}{\sqrt{2}}(\bar{u}u+\bar{d}d)|0>$, in order to search for the $σ$ meson. Our preliminary result shows that the connected and disconnected diagrams contribute to the $σ$ meson propagator in the same order.
We investigate high density state of SU(2) QCD by using Lattice QCD simulation with Wilson fermions. The ratio of fermion determinants is evaluated at each step of the Metropol is link update by Woodbury formula. At $β=0.7$, and $κ= 0.150$, we calculate the baryon number density, the Polyakov lines, and the energy density of gluon sector with chemical potential $μ$=0 to 0.8 on the $4^{3} \times 12$ lattice. Behavior of the meson propagators and diquark propagators with finite chemical potential are also investigated.
We investigate high density state of SU(2) QCD in the case of the Wilson fermions with Iwasaki improved action. Based on the Woodbery formula, the ratio of fermion determinants is evaluated at each step of the Metropolis link update. At $β=0.7$, for $κ= 0.150$, and $κ= 0.175$, we calculate thermodynamical quantities, such as, baryon number density, Polyakov line, and the energy density of gluon sector with chemical potential $μ$=0 to 0.9 on the $4^{3} \times 8$ lattice. The susceptibility of the Polyakov line to the chemical potential shows peak at around $μ= 0.7$ which indicates the deconfinement phase transition. Behavior of the meson and diquark propagators with finite chemical potential are also investigated at both side of the peak.
We evaluate charge diffusion constant of dense and hot hadronic matter based on the molecular dynamical method by using a hadronic collision generator which describes nuclear collisions at energies 10 < E < 100 GeV/A and satisfies detailed balance at low temperatures (T < 200 MeV). For the hot and dense hadronic matter of the temperature range, 100 < T < 200 MeV and baryon number density, 0.16 < nB < 0.32 fm^-3, charge diffusion constant D gradually increases from 0.5 fm c to 2 fm c with temperature and is almost independent of baryon number density. Based on the obtained diffusion constant we make simple discussions on the diffusion of charge fluctuation in ultrarelativistic nuclear collisions.
Using Wilson fermions, we study SU(2) lattice QCD with the chemical potential at $β=1.6$. The ratio of fermion determinants is evaluated at each Metropolis link update step. We calculate the baryon number density, the Polyakov loops and the pseudoscalar and vector masses on $4^4$ and $4^3\times 8$ lattices. Preliminary data show the pseudoscalar meson becomes massive around $μ=0.4$, which indicates the chiral symmetry restoration. The calculation is broken down when approaching to the transition region. We analyze the behavior of the fermion determinant and eigen value distributions of the determinant, which shows a peculiar ``Shell-and-Bean'' pattern near the transition.
We evaluate thermodynamical quantities and the transport coefficients of a dense and hot hadronic matter based on the event generator URASiMA (Ultra-Relativistic AA collision Simulator based on Multiple Scattering Algorithm) with periodic boundary conditions. As the simplest example of the transport coefficients we investigate the temperature dependence and the chemical potential dependence of the baryon diffusion constant of a dense and hot hadronic matter.
We generate the statistical ensembles in equilibrium with fixed temperature and chemical potential by imposing periodic boundary condition to the simulation of URASiMA(Ultra-Relativistic AA collision Simulator based on Multiple Scattering Algorithm). By using the generated ensembles, we investigate the temperature dependence and the chemical potential dependence of the nucleon diffusion constant of a dense and hot hadronic matter.
We evaluate thermodynamical quantities and transport coefficients of a dense and hot hadronic matter based on an event generator URASiMA (Ultra-Relativistic AA collision Simulator based on Multiple Scattering Algorithm). The statistical ensembles in equilibrium with fixed temperature and chemical potential are generated by imposing periodic boundary condition to the simulation of URASiMA, where energy density and baryon number density is conserved. Achievement of the thermal equilibrium and the chemical equilibrium are confirmed by the common value of slope parameter in the energy distributions and the saturation of the numbers of contained particles, respectively. By using the generated ensembles, we investigate the temperature dependence and the chemical potential dependence of the baryon diffusion constant of a dense and hot hadronic matter.
We investigate pion source sizes through the Yano-Koonin-Podgoretski\uı (YKP) parametrization for the Hanbury-Brown Twiss (HBT) effect in the CERN-SPS 158 GeV/A central collisions. We calculate two-particle correlation functions numerically based on a (3+1)-dimensional relativistic hydrodynamics with a first order phase transition and analyze the pair momentum dependence of the HBT radii extracted from the YKP parametrization in detail. We find that even in the case of a first order phase transition, expansion and the surface dominant freeze-out make the source in the hydrodynamical model opaque significantly. Consequently, the interpretation of the temporal radius parameter as the time duration becomes unavailable for the hydrodynamical model.
We numerically solve fully (3+1)-dimensional relativistic hydrodynamical equation coupled with the baryon number conservation law without spatial symmetry. We discuss the effect of transverse expansion based on the deviation our numerical result from Bjorken's scaling solution. We analyze the space-time evolution of the QGP gas in the case of non cylindrical initial conditions.
We numerically solve fully (3+1)-dimensional relativistic hydrodynamical equation with the baryon number conservation law. For realistic initial conditions we adopt the results from the event generator (URASiMA). Using this model we discuss collective flow.
We numerically solve the (3+1)-dimensional relativistic hydrodynamical equation with a bag-model equation of state, which is one of the simplest models for the first order phase transition. Based on the numerical solution, we discuss the space-time evolution of the hot fluid produced in ultra relativistic nuclear collisions. Especially, the space-time structure of the two-phase co-existing region during the quark-gluon plasma-hadron phase transition is analyzed in detail. Finally, we investigate the change of the mass spectra of $J/ψ$, $η_{c}$ and $ϕ$ as possible experimental signatures of the phase transition.
We calculate thermal photon and electron pair distribution from hot QCD matter produced in high energy heavy-ion collisions, based on a hydrodynamical model which is so tuned as to reproduce the recent experimental data at CERN SPS, and compare these electromagnetic spectra with experimental data given by CERN WA80 and CERES. We investigate mainly the effects of the off-shell properties of the source particles on the electromagnetic spectra.
We compare the numerical results of thermal photon distribution from the hot QCD matter produced by high energy nuclear collisions, based on hydrodynamical model, with the recent experimental data obtained by CERN WA80. Through the asymptotic value of the slope parameter of the transverse momentum distribution, we discuss the characteristic temperature of the QCD fluid.