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Kazuyuki Kanaya

Publications and source records attributed to Kazuyuki Kanaya.

50 records · Page 3Linked to original sources
arXiv2012

Numerical study of QCD phase diagram at high temperature and density by a histogram method

We study the QCD phase structure at high temperature and density adopting a histogram method. Because the quark determinant is complex at finite density, the Monte-Carlo method cannot be applied directly. We use a reweighting method and try to solve the problems which arise in the reweighting method, i.e. the sign problem and the overlap problem. We discuss the chemical potential dependence of the probability distribution function in the heavy quark mass region and examine the applicability of the approach in the light quark region.

hep-lat↗
arXiv2011

Finite Temperature QCD on the Lattice -- Status 2010

In the last couple of years, there has been big progress in finite temperature QCD on the lattice. Large-scale dynamical simulations of 2+1 flavor QCD with various improved staggered quark actions have been started to produce results for various thermodynamic quantities which are extrapolated to the continuum limit at around physical quark masses, and thus are capable for a direct comparison with experiment. At the same time, the theoretical uneasiness with staggered-type lattice quarks motivated several groups to accelerate studies with Wilson-type quarks and lattice chiral quarks. In this review, I discuss these important developments in finite temperature QCD made in the past year.

hep-lat↗
arXiv2008

Search for the Charmonium Dissociation Temperature with Variational Analysis in Lattice QCD

Charmonium dissociation temperatures are studied in a quenched anisotropic lattice QCD with standard plaquette gauge action and O(a) improved Wilson fermion action. Simulations are carried out at temperatures in the range 0.88T_c to 2.3T_c. From the meson correlators, we first subtract the contribution of constant mode, which was reported to mislead the analysis of, in particular, P wave signals. We then calculate effective masses and Bethe-Salpeter wave functions for ground (1S, 1P) and excited states (2S, 2P) using the multi-state variational analysis. To distinguish between bound states and scattering states, we apply two methods: First, we compare effective masses for charmonium correlation functions with finite spatial momenta under different spatial boundary conditions. Since the scattering state energies are sensitive to the boundary conditions, we expect finite volume effects when the charmonium dissociates. Second, we study the Bethe-Salpeter wave function, which should become broad when the charmonium bound state turns into a scattering state. With both methods, we have fond no clear evidences of dissociation for the ground and exited charmonium states up to 2.3T_c so far.

hep-lat↗
arXiv2006

Improvement of algorithms for dynamical overlap fermions

We investigate the algorithms for dynamical overlap fermions aiming at improving the performance for large-scale simulations. We look for the best combination of Hybrid Monte Carlo options and iterative quark solvers with respect to the numerical costs. Our main target is a $N_f=2$ simulation with overlap fermion on a $16^3\times 32$ lattice at lattice spacing around 0.12 fm.

hep-lat↗
arXiv2003

Three flavor dynamical QCD project by CP-PACS/JLQCD

The CP-PACS and JLQCD Collaborations have been made systematic studies of lattice QCD carrying out both chiral and continuum extrapolations. Importance of dynamical quark effects has been clarified by a comparison of quenched QCD and two flavor full QCD simulations. In two flavor simulations, the dynamical effects of $u$ and $d$ quarks are taken into account, but the third quark $s$ is still treated in a quenched approximation. As the final step towards a fully realistic lattice simulation of QCD, two collaborations started a joint project of three flavor QCD, concentrating all big computers available. Based on a series of preparative studies of exact simulation algorithm and non-perturbative improvement coefficient, a large scale simulation of three flavor QCD has been started. I present the results of light hadron spectrum and light quark masses from the first production runs.

hep-lat↗
arXiv2002

Recent lattice results relevant for heavy ion collisions

I summarize recent lattice results on QCD at finite temperatures and densities. Studies on the nature of the QCD transition at the physical point, continuum extra polations of thermodynamic quantities, and new calculations of hadronic spectral functions applying the maximum entropy method are discussed. Recent advances in finite density QCD are also reviewed.

hep-ph↗
arXiv2001

Elementary Particles on a Dedicated Parallel Computer

Numerical simulation of lattice QCD is now an indispensable tool for investigating non-perturbative properties of quarks at low energies. In this paper, I introduce a recent lattice QCD calculation of light hadron spectrum and quark masses performed on a dedicated parallel computer, CP-PACS. From a simulation of QCD with two flavors of dynamical quarks, we find $m_{ud}^{\bar{\rm MS}}(2{\rm GeV}) = 3.44^{+0.14}_{-0.22}$ MeV for the averaged mass of $u$ and $d$ quarks to reproduce the experimental masses of $π$ and $ρ$ mesons, and $m_{s}^{\bar{\rm MS}}(2{\rm GeV}) = 88^{+4}_{-6}$ MeV or $90^{+5}_{-11}$ MeV to reproduce the $K$ or $ϕ$ meson mass. These values are about 20--30% smaller than the previous estimates using the quenched approximation.

hep-ph↗
arXiv2001

Thermodynamic properties of QCD with two flavors of Wilson-type lattice quarks

I report on a study of finite temperature QCD by the CP-PACS Collaboration toward a precise determination of the equation of state with dynamical u,d quarks. Based on a systematic simulation using improved Wilson-type quarks on lattices with temporal size $N_t=4$ and 6, the energy density and pressure are calculated as functions of temperature and renormalized light quark mass in the range $T/T_c \approx 0.7$--2.5 and $m_{\rm PS}/m_{\rm V} = 0.65$--0.95. Results for $N_t=4$ are found to contain significant scaling violations, while results for $N_t=6$ are suggested to be not far from the continuum limit. On the other hand, the quark mass dependence in the EOS turned out to be small for $m_{\rm PS}/m_{\rm V} \simlt 0.8$.

hep-lat↗
arXiv2000

Dynamical Quark Effects in QCD on the Lattice - results from the CP-PACS

Results of a systematic lattice QCD simulation with two degenerate flavors of sea quarks, identified as dynamical u and d quarks, are presented. The simulation was performed on a dedicated parallel computer, called CP-PACS, developed at the University of Tsukuba. Clear dynamical quark effects are observed in the light hadron mass spectrum and in the light quark masses: In the light hadron mass spectrum, major parts of the discrepancy between quenched QCD and experiment are shown to be removed by introducing two flavors of dynamical quarks. For the averaged mass of u and d quarks, we find $m_{ud}^{\bar{\rm MS}}(2{\rm GeV}) = 3.44^{+0.14}_{-0.22}$ MeV using the $π$ and $ρ$ meson masses as physical input, and for the s quark mass, we obtain $m_{s}^{\bar{\rm MS}}(2{\rm GeV}) = 88^{+4}_{-6}$ MeV or $90^{+5}_{-11}$ MeV with the K or $ϕ$ meson mass as additional input. These values are about 20-30% smaller than the previous estimates in the quenched approximation. We also discuss the U(1) problem and B meson decay constants.

hep-ph↗
arXiv1997

Developments in Finite Temperature QCD on the Lattice with Dynamical Quarks

I report on some recent developments in nonperturbative studies of finite temperature QCD with dynamical quarks on the lattice. I discuss new studies of improved lattice actions and their application to finite temperature QCD. I also summarize the status of lattice investigations about the order of the finite temperature QCD transition for the case of two flavors of degenerate light quarks, using both staggered and Wilson lattice fermions.

hep-ph↗
arXiv1996

Simulations of the Finite Temperature QCD Phase Transition on the Lattice

I review the present status of nonperturbative studies on the nature of the finite temperature QCD transition on the lattice, with the special attention to the determination of the order of the transition. [Talk given at the International Symposium on {\it Origin of Matter and Evolution of Galaxies in the Universe}, Jan.\ 18 -- 20, 1996, Atami, Japan.]

astro-ph↗
arXiv1993

Interface tension in SU(3) lattice gauge theory at finite temperatures on an $N_t=2$ lattice

The surface tension $σ$ of the confined-deconfined interface is calculated in pure $SU(3)$ lattice gauge theory at finite temperatures employing the operator and integral methods on a lattice of a size $8^2\times N_z\times 2$ with $N_z=16$ and 40. Analyses of non-perturbative corrections in asymmetry response functions strongly indicate that the use of one-loop values for the response functions lead to an overestimate of $σ$ in the operator method. The operator method also suffers more from finite-size effects due to a finite thickness of the interface, leading us to conclude that the integral method yields more reliable values for $σ$. Our result with the integral method $σ/T_c^3=0.134(16)$ is consistent with earlier results and also with that obtained with a transfer matrix method. Result is also reported on $σ$ obtained on a lattice $18^2\times 48\times 4$ with the integral method.

hep-lat↗