Searcharxiv⌕ Search

arXiv subjects

Atsushi Nakamura

Publications and source records attributed to Atsushi Nakamura.

62 records · Page 4Linked to original sources
arXiv2002

Study of the Finite Density State based on SU(2) Lattice QCD

We report our recent numerical studies on two-color QCD with Wilson fermions. First the phase structure of the system in (kappa,mu)-plane is analyzed by measuring Polyakov line, baryon number density, gluon energy density and Polyakov line susceptibility. Then meson and baryon (di-quark) propagators are investigated. We find that the vector meson mass decreases near mu_c. This phenomena can be related to the low-mass lepton-pair enhancement observed in CERES experiment. Since our lattice is small, in order to confirm the results, we calculate both periodic and anti-periodic boundary condition cases. Preliminary calculations of color averaged, symmetric and anti-symmetric forces of qq system obtained from Polyakov line correlations, and gluon propagators are reported.

hep-lat↗
arXiv2001

Anisotropic Lattice and Its Application to Quark Gluon Plasma

We have studied the link-integration method for the improved actions. With this method the $η$ parameter in the medium to strong coupling regions is obtained. Effects of the self-energy terms for the $η$ parameters are small in the regions of $β$ and $η$ studied. After these investigations, the anisotropic lattice is used for the calculation of transport coefficients of the quark gluon plasma.

hep-lat↗
arXiv2000

Anisotropic Improved Actions

The studies of the quantum corrections for the anisotropy parameter,$η(=ξ_R/ξ_B)$, for the improved actions, $β(C_0 L({Plaq.}) + C_1 L({Rect.}))$, are proceeded in the medium to strong coupling region on anisotropic lattices. The global features for the $η$ parameters as a function of $β$ and the coefficient $C_{1}$ have been clarified. It has been found by the perturbative analysis that as $C_1$ decreases, the slope of the $η(β)$ becomes less steep and for the actions whose $C_{1}$ is less than -0.160, $η$ decreases as $β$ decreases, contrary to the case of the standard action. In the medium to strong coupling region, the $η$ parameter begins to increase as $β$ decreases for all $C_{1}$. This means that for the actions with $C_{1} < -0.160$, the one-loop perturbative results for $η$ break down qualitatively and the $η$ parameters have a dip. As a result of this dip structure the $η$ for Iwasaki's action remains close to unity in the wide range of $β$.

hep-lat↗
arXiv1998

Anisotropic Improved Gauge Actions; --Perturbative and Numerical Studies --

The $Λ$ parameter on the anisotropic lattice, the spatial and temperature coupling constant $g_σ$, $g_τ$ and their derivative with respaect to the the anisotropy parameter $ξ$ are studied perturbatively for the class of improved actions, which cover tree level Symanzik's, Iwasaki's and QCDTARO's improved actions. The $η(=g_τ/g_σ)$ becomes less than 1 for Iwasaki's and QCDTARO's action, which is confirmed nonperturbatively by numerical simulations. Derivatives of the coupling constants with respect to the anisotropy parameter, $\partial g_τ/\partial ξ$ and $\partial g_σ/\partial ξ$, change sign for those improved actions.

hep-lat↗
arXiv1998

Transport Coefficients of Quark Gluon Plasma From Lattice Gauge Theory

Numerical results for the transport coefficients of quark gluon plasma are obtained by lattice simulations on on $16^3 \times 8$ lattice with the quench approximation where we apply the gauge action proposed by Iwasaki. The bulk viscosity is consistent with zero, and the shear viscosity is slightly smaller than the typical hadron masses. They are not far from the simple extrapolation on the figure of perturbative calculation in high temperature limit down to $T \sim T_{c}$. The gluon propagator in the confined and deconfined phases are also discussed.

hep-lat↗
arXiv1996

Transport Coefficients of Quark Gluon Plasma for Pure Gauge Models

The transport coefficients of quark gluon plasma are calculated on a lattice 16**3X8, with the pure gauge models. Matsubara Green's functions of energy momentum tensors have very large fluctuations and about a few million MC sweeps are needed to reduce the errors reasonably small in the case of the standard action. They are much suppressed if Iwasaki's improved action is employed. Preliminary results show that the transport coefficients roughly depend on the coupling constant as a**(-3)(g) in the case of SU(2).

hep-lat↗
arXiv1995

Bosonization of Thirring Model in Arbitrary Dimension

We propose to use a novel master Lagrangian for performing the bosonization of the $D$-dimensional massive Thirring model in $D=d+1 \ge 2$ dimensions. It is shown that our master Lagrangian is able to relate the previous interpolating Lagrangians each other which have been recently used to show the equivalence of the massive Thirring model in (2+1) dimensions with the Maxwell-Chern-Simons theory. Starting from the phase-space path integral representation of the master Lagrangian, we give an alternative proof for this equivalence up to the next-to-leading order in the expansion of the inverse fermion mass. Moreover, in (3+1)-dimensional case, the bosonized theory is shown to be equivalent to the massive antisymmetric tensor gauge theory. As a byproduct, we reproduce the well-known result on bosonization of the (1+1)-dimensional Thirring model following the same strategy. Finally a possibility of extending our strategy to the non-Abelian case is also discussed.

hep-th↗