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A. Nakamura

Publications and source records attributed to A. Nakamura.

At least 73 records · Page 4Linked to original sources

Responses of quark condensates to the chemical potential

The responses of quark condensates to the chemical potential, as a function of temperature T and chemical potential μ, are calculated within the Nambu--Jona-Lasinio (NJL) model. We compare our results with those from the recent lattice QCD simulations [QCD-TARO Collaboration, Nucl. Phys. B (Proc. Suppl.) 106, 462 (2002)]. The NJL model and lattice calculations show qualitatively similar behavior, and they will be complimentary ways to study hadrons at finite density. The behavior above T_c requires more elaborated analyses.

hep-lat↗

Renormalization group flow of SU(3) lattice gauge theory - Numerical studies in a two coupling space

We investigate the renormalization group (RG) flow of SU(3) lattice gauge theory in a two coupling space with couplings $β_{11}$ and $β_{12}$ corresponding to $1\times 1$ and $1\times 2$ loops respectively. Extensive numerical calculations of the RG flow are made in the fourth quadrant of this coupling space, i.e., $β_{11}>0$ and $β_{12}<0$. Swendsen's factor two blocking and the Schwinger-Dyson method are used to find an effective action for the blocked gauge field. The resulting renormalization group flow runs quickly towards an attractive stream which has an approximate line shape. This is numerical evidence of a renormalized trajectory which locates close to the two coupling space. A model flow equation which incorporates a marginal coupling (asymptotic scaling term), an irrelevant coupling and a non-perturbative attraction towards the strong coupling limit reproduces qualitatively the observed features. We further examine the scaling properties of an action which is closer to the attractive stream than the currently used improved actions. It is found that this action shows excellent restoration of rotational symmetry even for coarse lattices with $a \sim 0.3$ fm.

hep-lat↗

Complex Diffusion Monte-Carlo method: tests by the simulations of 2D electron in magnetic field and 2D fermions-anyons in parabolic well

We propose a new Complex Diffusion Monte Carlo (CDMC) method for the simulation of quantum systems with complex wave function. In CDMC the modulus and phase of wave function are simulated both in contrast to other methods. We successfully test CDMC by the simulation of the ground state for 2D electron in magnetic field and 2D fermions-anyons in parabolic well.

cond-mat↗

I=0 scalar channel

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.

hep-lat↗

Lattice Study of the High Density State of SU(2)-QCD

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.

nucl-th↗

Study of the SU(2) High Density System with Wilson Fermion

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.

hep-lat↗

Screening mass responses to the chemical potential at finite temperature

Responses to chemical potential of the pseudoscalar meson screening mass and the chiral condensate in lattice QCD are investigated. On a $16 \times 8^2 \times \4$ lattice with two flavors of staggered quarks the first and second responses below and above $T_c$ are evaluated. Different behavior in the low and the high temperature phases are observed, which may be explained as a consequence of the chiral symmetry breaking and restoration.

hep-lat↗

Responses of hadrons to chemical potential at finite temperature

We present a framework to compute the responses of hadron masses to the chemical potential in lattice QCD simulations. As a first trial, the screening mass of the pseudoscalar meson and its first and second responses are evaluated. We present results on a $16\times 8^2\times 4$ lattice with two flavors of staggered quarks below and above $T_c$. The responses to both the isoscalar and isovector chemical potentials are obtained. They show different behavior in the low and the high temperature phases, which may be explained as a consequence of chiral symmetry breaking and restoration, respectively.

hep-lat↗

Quenched charmonium near the continuum limit

We study relativistic charmonium on very fine quenched lattices (beta=6.4 and 6.6). We concentrate on the calculation of the hyperfine splitting between eta_c and J/psi, aiming for a controlled continuum extrapolation of this quantity. Results for the eta_c and J/psi wave functions are also presented.

hep-lat↗

Complex diffusion Monte-Carlo method: test by the simulation of the 2D fermions

On the base of the diffusion Monte-Carlo method we develop the method allowing to simulate the quantum systems with complex wave function. The method is exact and there are no approximations on the simulations of the module and the phase of the system's wave function. In our method averaged value of any quantity have no direct contribution from the phase of distribution function but only from the phase of the Green function of diffusion equation. We test the method by the simulations of the ground state of fermions in two-dimensional parabolic well. Anyons are used for the representation of the two-dimensional (2D) fermions. We vary the number of fermions from two to ten and find a good agreement of the numerical results with analytical ones for the numbers of the particles N > 4.

cond-mat↗

Complex Diffusion Monte-Carlo method for the systems with complex wave function: test by the simulation of 2D electron in uniform magnetic field

On the base of Diffusion Monte-Carlo method it is developed a new Complex Diffusion Monte-Carlo (CDMC) method allowing to simulate the quantum systems with complex wave function. There are no approximations on the calculation of modulus and phase of wave function in contrast to other methods. We find that the averaged value of any quantity in CDMC will have no direct contribution from the phase of the distribution function but only from the phase of the Green function of the diffusion equation. This is most important and crucial point of CDMC. We are testing CDMC by the calculation of the wave function and the ground state energy of two-dimensional electron placed into the external uniform magnetic field. There is an excellent agreement between simulations results and an analytical ones.

cond-mat↗

Approximate formula for the ground state energy of anyons in 2D parabolic well

We determine approximate formula for the ground state energy of anyons in 2D parabolic well which is valid for the arbitrary anyonic factor νand number of particles N in the system. We assume that centre of mass motion energy is not excluded from the energy of the system. Formula for ground state energy calculated by variational principle contains logarithmic divergence at small distances between two anyons which is regularized by cut-off parameter. By equating this variational formula to the analogous formula of Wu near bosonic limit (ν~ 0)we determine the value of the cut-off and thus derive the approximate formula for the ground state energy for the any νand N. We checked this formula at ν=1, when anyons become fermions, for the systems containing two to thirty particles. We find that our approximate formula has an accuracy within 6%. It turns out, at the big number N limit the ground state energy has square root dependence on factor ν.

cond-mat↗

Chemical potential response of meson masses at finite temperature

We study the response of meson masses to the chemical potential ($\partial{m}/\partialμ$) at high temperature and at zero chemical potential on $N_f=2$ lattice with staggered fermions. Preliminary results for the meson composed of different quarks show that $\partial{m}/\partialμ|_{μ=0}$ is negative in the confinement phase and positive in the deconfinement phase.

hep-lat↗

Monte Carlo Study of Two-Color QCD with Finite Chemical Potential - Status report of Wilson fermion simulation

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.

hep-lat↗

Simulation of SU(2) Dynamical Fermion at Finite Chemical Potential and at Finite Temperature

SU(2) lattice gauge theory with dynamical fermion at non-zero chemical potential and at finite temperature is studied. We focus on the influence of chemical potential for quark condensate and mass of pseudoscalar meson at finite temperature. Hybrid Monte Carlo simulations with $N_f=8$ staggered fermions are carried out on $12 \times 12\times 24 \times 4$ lattice. At $β=1.1$ and $m_{q}=$0.05,0.07,0.1, we calculate the quark condensate and masses of pseudoscalar meson consisting of light and heavier quarks for chemical potential $μ=$ 0.0,0.02,0.05,0.1,0.2.

hep-lat↗

Observation of anomalous single-magnon scattering in half-metallic ferromagnets by chemical pressure control

Temperature variation of resistivity and specific heat have been measured for prototypical half-metallic ferromagnets, R_0.6Sr_0.4MnO_3, with controlling the one-electron bandwidth W. We have found variation of the temperature scalings in the resistivity from T^2 (R = La, and Nd) to T^3 (R = Sm), and have interpreted the $T^3-law in terms of the anomalous single-magnon scattering (AMS) process in the half-metallic system.

cond-mat.str-el↗

Meson Correlators in Finite Temperature Lattice QCD

We analyze temporal and spatial meson correlators in quenched lattice QCD at T>0. Below T_c we observe little change in the meson properties as compared with T=0. Above T_c we observe new features: chiral symmetry restoration and signals of plasma formation, but also indication of persisting mesonic (metastable) states and different temporal and spatial masses in the mesonic channels. This suggests a complex picture of QGP in the region 1 - 1.5 T_c.

hep-lat↗

Improved Gauge Actions on Anisotropic Lattices I

On anisotropic lattices with the anisotropy $ξ=a_σ/a_τ$ the following basic parameters are calculated by perturbative method: (1) the renormalization of the gauge coupling in spatial and temporal directions, $g_σ$ and $g_τ$, (2) the $Λ$ parameter, (3) the ratio of the renormalized and bare anisotropy $η=ξ/ξ_B$ and (4) the derivatives of the coupling constants with respect to $ξ$, $\partial g_σ^{-2}/\partial ξ$ and $\partial g_τ^{-2}/\partial ξ$. We employ the improved gauge actions which consist of plaquette and six-link rectangular loops, $c_0 P(1 \times 1)_{μν} + c_1 P(1 \times 2)_{μν}$. This class of actions covers Symanzik, Iwasaki and DBW2 actions. The ratio $η$ shows an impressive behavior as a function of $c_{1}$, i.e.,$η>1$ for the standard Wilson and Symanzik actions, while $η<1$ for Iwasaki and DBW2 actions. This is confirmed non-perturbatively by numerical simulations in weak coupling regions. The derivatives $\partial g^{-2}_τ/\partial ξ$ and $\partial g^{-2}_σ/\partial ξ$ also changes sign as $-c_{1}$ increases. For Iwasaki and DBW2 actions they become opposite sign to those for standard and Symanzik actions. However, their sum is independent of the type of actions due to Karsch's sum rule.

hep-lat↗