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Yoshinobu Kuramashi

Publications and source records attributed to Yoshinobu Kuramashi.

At least 91 records · Page 5Linked to original sources
arXiv2015

Study of quark mass dependence of binding energy for light nuclei in 2+1 flavor lattice QCD

We investigate the formation of light nuclei with the nuclear mass number less than or equal to four in 2+1 flavor QCD using a non-perturbative improved Wilson quark and Iwasaki gauge actions. The quark mass is decreased from our previous work to the one corresponding to the pion mass of 0.30 GeV. In each multi-nucleon channel, the energy shift of the ground state relative to the assembly of free nucleons is calculated on two volumes, whose spatial extents are 4.3 fm and 5.8 fm. From the volume dependence of the energy shift, we distinguish a bound state of multi nucleons from an attractive scattering state. We find that all the ground states measured in this calculation are bound states. As in the previous studies at larger $m_π$, our result indicates that at $m_π= 0.30$ GeV the effective interaction between nucleons in the light nuclei is relatively stronger than the one in nature, since the results for the binding energies are larger than the experimental values and a bound state appears in the dineutron channel, which is not observed in experiment. Possible sources of systematic error in this calculation are discussed.

hep-lat↗
arXiv2015

Scalar correlators near the 3-flavor thermal critical point

We investigate screening masses at both sides of the first order finite temperature transition with 3 quark flavors using the nonperturbatively improved clover fermion action and the Iwasaki gauge action. We have developed the method of hierarchical truncations with stochastic probing to accelerate the noise estimator for evaluating quark loops at every spatial lattice slices. At parameter values we study, the flavor singlet scalar meson has a screening mass about half of the pion screening mass. It becomes lighter as the system approaches the critical endpoint.

hep-lat↗
arXiv2014

Critical endpoint of finite temperature phase transition for three flavor QCD

We investigate the critical endpoint of finite temperature phase transition of $N_f=3$ QCD at zero chemical potential. We employ the renormalization-group improved Iwasaki gauge action and non-perturbatively $O(a)$-improved Wilson-clover fermion action. The critical endpoint is determined by using the intersection point of kurtosis for the temporal size $N_t$=4, 6, 8. Spatial sizes of $N_l$=6-16 ($N_t$=4), 10-24 ($N_t$=6), and 12-24 ($N_t$=8) are employed. We find that $N_t$=4 is out of the scaling region. Using results for $N_t$=6 and 8, and making linear extrapolations in $1/N_t^2$, we obtain $\sqrt{t_0}T_{\rm E}=0.0975(14)(8)$, $\sqrt{t_0}m_{\rm PS,E}=0.2254(52)(105)$ and $m_{\rm PS,E}/T_{\rm E}=2.311(63)(13)$, where the first error is statistical error, the second error is systematic error, and $m_{\rm PS}$ is the pseudo scalar meson mass. If one uses $1/\sqrt{t_0}=1.347(30)$ GeV reported by Borsanyi et al., one finds $T_{\rm E}=131(2)(1)(3)$ MeV, $m_{\rm PS,E}=304(7)(14)(7)$ MeV and $m_{\rm PS,E}/m_{\rm PS,E}^{\rm phys, sym}=0.739(17)(34)(17)$, where the third error comes from error of $\sqrt{t_0}$ and $m_{\rm PS}^{\rm phys, sym}=\sqrt{(m_π^2+2m_K^2)/3}$. Our current estimation of $\sqrt{t_0}m_{\rm PS,E}$ in the continuum limit is about 25% smaller than the SU(3) symmetric point.

hep-lat↗
arXiv2014

Critical end point of Nf=3 QCD at finite temperature and density

We investigate the phase structure of 3-flavor QCD in the presence of finite quark chemical potential $aμ=0.1$ by using the Wilson-Clover fermion action. Especially, we focus on locating the critical end point that characterizes the phase structure. We do this by the kurtosis intersection method for the quark condensate. For Wilson-type fermions, the correspondence between bare parameters and physical parameters is indirect. Hence we present a strategy to transfer the bare parameter phase structure to the physical one.

hep-lat↗
arXiv2014

Critical behavior of lattice Schwinger model with topological term at $θ=π$ using Grassmann tensor renormalization group

Lattice regularized Schwinger model with a so-called $θ$ term is studied by using the Grassmann tensor renormalization group. We perform the Lee-Yang and Fisher zero analyses in order to investigate the phase structure at $θ=π$. We find a first order phase transition at larger fermion mass. Both of the Lee-Yang zero and Fisher zero analyses indicate that the critical endpoint at which the first order phase transition terminates belongs to the Ising universality class.

hep-lat↗
arXiv2014

Grassmann Tensor Renormalization Group Approach to One-Flavor Lattice Schwinger Model

We apply the Grassmann tensor renormalization group to the lattice regularized Schwinger model with one-flavor of the Wilson fermion. We study the phase diagram in the $(β,κ)$ plane performing a detailed analysis of the scaling behavior of the Lee-Yang zeros and the peak height of the chiral susceptibility. Our results strongly indicate that the whole range of the phase transition line starting from $(β,κ)=(0.0,0.380665(59))$ and ending at $(\infty,0.25)$ belongs to the two-dimensional Ising universality class similarly to the free fermion case.

hep-lat↗
arXiv2013

Zeros of QCD partition function from finite density lattices

Partition function zeros steer the critical behavior of a system. Studying four-flavor lattice QCD at finite temperature and density with the Wilson-clover fermion action and the Iwasaki gauge action using a phase-quenched fermion determinant, we combine statistics from multiple chemical potentials to improve sampling of the configuration space, and aim at unraveling the movement of zeros in finite systems. Preparing for further investigations, we discuss methods and criteria used to sieve through complex parameter space spanned by $(\text{Re}μ, \text{Im}μ)$ and $(\text{Re}μ, \text{Im}β)$, and present statistically robust zeros of the partition function.

hep-lat↗
arXiv2013

Multi-nucleon bound states in $N_f=2+1$ lattice QCD

We report on our on-going effort to calculate the properties of light nuclei directly from quarks and gluons based on lattice QCD. After briefly introducing our motivations and aims, we describe our strategy of fixing the strange quark mass at its physical value and approaching the physical point for the up and down quark masses step by step from the region of heavy quark masses. A successful calculation for the pion mass of 0.51GeV is reviewed, and the status for a lighter pion mass of 0.30GeV is reported.

hep-lat↗
arXiv2013

Finite size scaling study of $N_{\text{f}}=4$ finite density QCD on the lattice

We explore the phase space spanned by the temperature and the chemical potential for 4-flavor lattice QCD using the Wilson-clover quark action. In order to determine the order of the phase transition, we apply finite size scaling analyses to gluonic and quark observables including plaquette, Polyakov loop and quark number density, and examine their susceptibility, skewness, kurtosis and Challa-Landau-Binder cumulant. Simulations were carried out on lattices of a temporal size fixed at $N_{\text{t}}=4$ and spatial sizes chosen from $6^3$ up to $10^3$. Configurations were generated using the phase reweighting approach, while the value of the phase of the quark determinant were carefully monitored. The $μ$-parameter reweighting technique is employed to precisely locate the point of the phase transition. Among various approximation schemes for calculating the ratio of quark determinants needed for $μ$-reweighting, we found the Taylor expansion of the logarithm of the quark determinant to be the most reliable. Our finite-size analyses show that the transition is first order at $(β, κ, μ/T)=(1.58, 0.1385, 0.584\pm 0.008)$ where $(m_π/m_ρ, T/m_ρ)=(0.822, 0.154)$. It weakens considerably at $(β, κ, μ/T)=(1.60, 0.1371, 0.821\pm 0.008)$ where $(m_π/m_ρ, T/m_ρ)=(0.839, 0.150)$, and a crossover rather than a first order phase transition cannot be ruled out.

hep-lat↗
arXiv2012

Bound states of multi-nucleon channels in N_f=2+1 lattice QCD

We calculate the energies for multi-nucleon ground states with the nuclear mass number less than or equal to 4 in 2+1 flavor QCD at the lattice spacing of a = 0.09 fm employing a relatively heavy quark mass corresponding to m_pi = 0.51 GeV. We investigate the volume dependence of the energy shift of the ground state and the state of free nucleons to distinguish a bound state from attractive scattering states. From the investigation we conclude that ^4He, ^3He, deuteron and dineutron are bound at m_pi = 0.51 GeV. We compare their binding energies with those in our quenched studies and also with some recent investigations.

hep-lat↗
arXiv2012

Finite size scaling for 4-flavor QCD with finite chemical potential

We explore the phase diagram spanned by the temperature and the chemical potential for 4-flavor QCD by the phase-reweighting approach. In order to determine the order of phase transition, we perform finite size scaling studies for various quantities, for example, susceptibility, kurtosis and Challa-Landau-Binder cumulant. At the parameter (beta=1.60, kappa=0.1371, c_sw=1.9655 and N_T=4), where the Kentucky group reported a first-order phase transition in their canonical simulation, we observe that the transition is consistent with being of first order.

hep-lat↗
arXiv2012

Helium nuclei, deuteron and dineutron in 2+1 flavor lattice QCD

We calculate the binding energies for multi-nucleon bound states with the nuclear mass number less than or equal to 4 in 2+1 flavor QCD at the lattice spacing of a = 0.09 fm employing a relatively heavy quark mass corresponding to m_pi = 0.51 GeV. To distinguish a bound state from attractive scattering states, we investigate the volume dependence of the energy shift between the ground state and the state of free nucleons by changing the spatial extent of the lattice from 2.9 fm to 5.8 fm. We conclude that ^4He, ^3He, deuteron and dineutron are bound at m_pi = 0.51 GeV. We compare their binding energies with those in our quenched studies and also with several previous investigations.

hep-lat↗
arXiv2011

On the phase of quark determinant in lattice QCD with finite chemical potential

We investigate the phase of the quark determinant with finite chemical potential in lattice QCD using both analytic and numerical methods. Applying the winding number expansion and the hopping parameter expansion to the logarithm of the determinant, we show that the absolute value of the phase has an upper bound that grows with the spatial volume but decreases exponentially with an increase in the temporal extent of the lattice. This analytic but approximate result is confirmed with a numerical study in four-flavor QCD in which the phase is calculated exactly. Since the phase is well controlled on lattices with larger time extents, we try the phase reweighting method in a region beyond $μ/T=1$ where the Taylor expansion method cannot be applied. Working in four-flavor QCD, we find a first-order like behavior on a $6^3\times 4$ lattice at $μ/T\approx 0.8$ which was previously observed by Kentucky group with the canonical method. We also show that the winding number expansion has a nice convergence property beyond $μ/T=1$. We expect that this expansion is useful to study the high density region of the QCD phase diagram at low temperatures.

hep-lat↗
arXiv2008

PACS-CS results for 2+1 flavor lattice QCD simulation on and off the physical point

We report on the PACS-CS project focusing on a direct simulation of 2+1 flavor QCD on the physical point and chiral analysis of meson and baryon masses off the physical point with both the SU(2) and SU(3) chiral perturbation theories. Configurations are generated with the O(a)-improved Wilson quark action and the Iwasaki gauge action. The up-down quark is simulated by employing the DDHMC algorithm with several improvements and the UV-filtered PHMC algorithm is implemented for the strange quark. We investigate the convergence behaviors of the SU(2) and SU(3) chiral expansions up to NLO for the pseudoscalar meson sector, where the up-down quark mass ranges from 3 MeV to 24 MeV and the strange quark mass is chosen around the physical value. The fit results for the low energy constants are compared with those recently obtained by other groups. We also discuss the importance of the direct simulation at the physical point by comparing the physical quantities measured on the physical point with those estimated by the extrapolation method.

hep-lat↗
arXiv2007

Nf=2+1 dynamical Wilson quark simulation toward the physical point

We present preliminary results of the PACS-CS project which simulates 2+1 flavor lattice QCD toward the physical point with the nonperturbatively O(a)-improved Wilson quark action and the Iwasaki gauge action. Calculations are carried out at beta=1.9 on a 32^3x64 lattice with the use of the domain-decomposed HMC algorithm to reduce the up-down quark mass. The resulting pseudoscalar meson masses range from 730 MeV down to 210 MeV. We discuss the physical results including the chiral analysis in the pseudoscalar meson sector and the hadron spectrum. Some algorithmic issues are also discussed.

hep-lat↗
arXiv2006

Perturbative renormalization factors for generic $Δs=2$ four-quark operators in domain-wall QCD with improved gauge action

We calculate one-loop renormalization factors of generic DeltaS=2 four-quark operators for domain-wall QCD with the plaquette gauge action and the Iwasaki gauge action. The renormalization factors are presented in the modified minimal subtraction (MS-bar) scheme with the naive dimensional regularization. As an important application we show how to construct the renormalization factors for the operators contributing to K^0-K^0bar mixing in the supersymmetric models with the use of our results.

hep-lat↗
arXiv2004

One-loop determination of mass dependent $O(a)$ improvement coefficients for the heavy-light vector and axial-vector currents with relativistic heavy and domain-wall light quarks

We present the one-loop results of the mass dependent $O(a)$ improvement coefficients for the heavy-light vector and axial-vector currents consisting of the relativistic heavy and the domain-wall light quarks. The calculations are performed with the plaquette, Iwasaki and DBW2 gauge actions. The heavy quark mass and domain-wall height dependence is investigated. We point out that the exact chiral symmetry held by the lattice light quark action leads to an exact relation between the improvement coefficients for the vector and axial-vector currents without regard to the lattice heavy quark action.

hep-lat↗