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Suguru Sato, Junpei Saito, Atsuro Fukuhara, Manabu Uematsu, Yasuhito Suzuki, Mami Rikimaru, Takaya Kawamata, Takashi Umeda, Tatsuhiko Koizumi, Ryuichi Togawa, Yuki Sato, Takefumi Nikaido, Hiroyuki Minemura, Kenya Kanazawa, Yoshinori Tanino, Yoko Shibata Department of Pulmonary Medicine, School of Medicine, Fukushima Medical University, Fukushima, 960-1295, JapanCorrespondence: Suguru SatoDepartment of Pulmonary Medicine, School of Medicine, Fukushima Medical University, Hikarigaoka-1, Fukushima, 960-1295, JapanTel +81-24-547-1360Fax +81-24-548-9366Email suguru@fmu.ac.jpBackground: Nocturnal asthma symptoms are a well-known feature of sleep disturbance. However, there are few reports on the association between sleep-related characteristics and asthma exacerbation. The aim of the current prospective observational study was to explore the factors while sleeping associated with future asthma exacerbation.Materials and Methods: At baseline, adult asthmatics underwent home sleep monitoring by a Watch-PAT instrument and then they were prospectively followed-up for the occurrence of exacerbations. The number of asthma exacerbation was observed over a period of one year, and multivariable analyses of the factors associated with asthma exacerbation were performed.Results: A total of 62 asthmatic subjects were enrolled (mean age 62.1 years), 59 of whom were finally included in the prospective observational study. Obstructive sleep apnea (defined by an apnea-hypopnea index based on peripheral arterial tone more than 5 times/hour) were observed in 81% of the subjects. During the one-year monitoring period, 14 of the 59 subjects (24%) used occasional systemic corticosteroids for their exacerbation asthma (worsened group) while the other 45 subjects did not experience asthma exacerbation (stable group). A comparison of the baseline clinical characteristics and sleep-related data between the two groups, mean forced expiratory volume one second percent (FEV1/FVC), mean baseline Asthma Control Test (ACT) score, median pAHI value, and median oxygen desaturation index value were significantly lower in the worsened group than those in the stable group. Additionally, mean prevalence of the left lateral decubitus (LLD) position in sleep monitoring were significantly higher in the worsened group than that in the stable group. Among the independent variables, baseline asthma severity, ACT score, and the LLD position showed significant associations with asthma exacerbation.Discussion/Conclusion: The present study identified that sleeping in the LLD position was also associated with asthma exacerbation.Keywords: asthma, asthma control, sleep position, asthma exacerbation

IIa型合成ダイヤモンド単結晶のEPR（電子スピン共鳴）に関する研究, 14th International Conference on New Diamond and Nano Carbons 2020/2021

Impurity-vacancy complexes in diamond are an attractive family of spin defects since NV−, SiV−, GeV−, and SnV− have emerged as promising platforms for quantum applications. Although boron is most easily incorporated into diamond, a boron-vacancy complex in the negative charge state (BV−) has eluded experimental observation. This center was theoretically predicted as another promising spin qubit. In this work, we experimentally observed an electron paramagnetic resonance (EPR) spectrum identified as BV− in synthetic diamonds via a Fermi-level tuning. Fingerprints of BV− such as the spin multiplicity of S= 1,C3v symmetry, the zero-field splitting (D= 2913 MHz), in addition to 10B and 11 B hyperfine (HF) interactions have been confirmed. Moreover, optically-pumped spin polarization has been observed with 3.0 to 3.6 eV excitation. However, unlike the NV− center, the photoluminescence as well as optically detected magnetic resonance from BV− has not been confirmed even at low temperatures. We speculate that the Jahn-Teller instability in the triplet states of the NV− and BV− centers results in different optical properties.

We extend our previous study of the QCD phase structure in the heavy quark region to non-zero chemical potentials. To identify the critical point where the first order deconfining transition terminates, we study an effective potential defined by the probability distribution function of the plaquette and the Polyakov loop. The reweighting technique is shown to be powerful in evaluating the effective potential in a wide range of the plaquette and Polyakov loop expectation values. We adopt the cumulant expansion to overcome the sign problem in the calculation of complex phase of the quark determinant. We find that the method provides us with an intuitive and powerful way to study the phase structure. We estimate the location of the critical point at finite chemical potential in the heavy quark region., The XXIX Internaitonal Symposium on Lattice Field Theory, Lattice2011 July 11-16, 2011 The Village at Squaw Valley, US

We propose a new approach to finite density QCD based on a histogram method with phase quenched simulations at finite chemical potential. Integrating numerically the derivatives of the logarithm of the quark determinant with respect to the chemical potential, we calculate the reweighting factor and the complex phase of the quark determinant. The complex phase is handled with a cumulant expansion to avoid the sign problem. We examine the applicability of this method., The XXIX Internaitonal Symposium on Lattice Field Theory, Lattice2011 July 10-16, 2011 Squaw Lake Tahoe, California

We present a new method to calculate meson spectral functions (SPFs) on the lattice based on a variational method. Because, on a finite volume lattice, the meson SPFs have discrete spectra only, a suitable way to extract such discrete signals is needed. Using a variational method, we can calculate several discrete quantities such as the position and the area of spectral peaks for low-lying states. Moreover data accuracy can be improved by increasing the number of basis functions. In this report, we first confirm our method in the free quark case and show that our method works well. Then, we apply the method to a quenched lattice QCD simulation and calculate the charmonium SPFs for S and P-waves at zero temperature. Our results for the ground state are well consistent with the position and the area of the lowest peaks of charmonium SPFs calculated by the conventional maximum entropy method. For first excited states, the signals may be reliablly extracted with our method because the charmonium mass converges to a value close to the experimental one when the number of basis functions is increased. We also investigate the SPFs for S-wave charmonia at below and above Tc. Our results suggest that J/y and hc may survive up to 1.4Tc., The XXVIII Internaitonal Symposium on Lattice Field Theory, Lattice2010 July 14-19, 2010 Villasimius, Italy

We study the quark mass dependence of the QCD phase transition by an effective potential defined through the distribution function of observables. As a test of the method, we study the first order deconfinement phase transition in the heavy quark mass limit and its fate at lighter quark masses. We confirm that the distribution function for the plaquette has two peaks indicating that the phase transition is of first order in the heavy quark limit. We then study the quark mass dependence of the distribution function by a reweighting method combined with the hopping parameter expansion. We find that the first order transition turns into a crossover as the quark mass decreases. We determine the critical point for the cases of Nf = 1, 2, 3 and 2+1. We find that the probability distribution function provides us with a powerful tool to study the order of transitions., The XXVIII Internaitonal Symposium on Lattice Field Theory, Lattice2010 July 14-19, 2010 Villasimius, Italy

We present the status of our study on the equation of state in 2+1 flavor QCD with nonperturbatively improved Wilson quarks coupled with the RG improved glue. We apply the Tintegration method to non-perturbatively calculate the equation of state by the fixed-scale approach., The XXVIII Internaitonal Symposium on Lattice Field Theory, Lattice2010 July 14-19, 2010 Villasimius, Italy

We study scaling behavior of a chiral order parameter performing a simulation of two-flavor QCD with improved Wilson quarks. It has been shown that the scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the threedimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Calculating derivatives of the chiral order parameter with respect to the chemical potential in two-flavor QCD, the scaling property of chiral phase transition is discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chirl phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation., The XXVIII Internaitonal Symposium on Lattice Field Theory, Lattice2010 July 14-19, 2010 Villasimius, Sardinia Italy

We report on the status of our study towards the equation of state in 2+1 flavor QCD with improvedWilson quarks. To reduce the computational cost which is quite demanding for Wilson-type quarks, we adopt the fixed scale approach, i.e. the temperature T is varied by Nt at fixed lattice spacing. Since the conventional integral method to obtain the pressure is inapplicable at a fixed scale, we adopt the T-integral method, to calculate the pressure non-perturbatively. Reduction of the computational cost of T = 0 simulations thus achieved is indispensable to study EOS in QCD with dynamical quarks., The XXVII Internaitonal Symposium on Lattice Field Theory - LAT2009 July 26-31, 2009 Peking University, Beijing, China

The free energy between a static quark and an antiquark is studied by using the color-singlet Polyakov-line correlation at finite temperature. We perform simulations on 323 £12, 10, 8, 6, 4 lattices in the high temperature phase with the RG-improved gluon action and 2+1 flavors of the clover-improvedWilson quark action. Since the simulations are based on the fixed scale approach that the temperature can be varied without changing the spatial volume and renormalization factor, it is possible to investigate temperature dependence of the heavy-quark free energy without any adjustment of the overall constant. We find that, the heavy-quark free energies at short distance converge to the heavy-quark potential evaluated from the Wilson-loop operator at zero temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the heavy-quark free energies approach to twice the single-quark free energies, implying that the interaction between heavy quarks is screened. The Debye screening mass obtained from the long range behavior of the heavy-quark free energy is compared with results of the thermal perturbation theory and those of Nf = 2 and Nf = 0 lattice simulations., The XXVII Internaitonal Symposium on Lattice Field Theory, July 26-31, 2009 Peking University, Beijing, China

We study thermodynamics of SU(3) gauge theory at xed scales on the lattice, where we vary temperature by changing the temporal lattice size Nt =(Tat )����1. In the xed scale approach, nite temperature simulations are performed on common lattice spacings and spatial volumes. Consequently, we can isolate thermal effects in observables from other uncertainties, such as lattice artifact, renormalization factor, and spatial volume effect. Furthermore, in the EOS calculations, the xed scale approach is able to reduce computational costs for zero temperature subtraction and parameter search to nd lines of constant physics, which are demanding in full QCD simulations. As a test of the approach, we study the thermodynamics of the SU(3) gauge theory on isotropic and anisotropic lattices. In addition to the equation of state, we calculate the critical temperature and the static quark free energy at a xed scale., The XXVI Internaitonal Symposium on Lattice Field Theory July 14-19 2008 Williamsburg, Virginia, USA

Screening properties of the quark gluon plasma are studied from the Polyakov-line correlations in lattice QCD simulations with two flavors of improvedWilson quarks at temperatures T=Tpc '1–4 where Tpc is the pseudocritical temperature. Using the Euclidean-time reflection symmetry and the charge conjugation symmetry, we introduce various types of Polyakov-line correlations and extract screening masses in magnetic and electric sectors. We find that a ratio of the screening masses in the electric sector to the magnetic sector shows qualitative agreement with a prediction from the dimensionally-reduced effective field theory and theN =4 supersymmetric Yang-Mills theory at 1:3 < T=Tpc < 3., The XXVI Internaitonal Symposium on Lattice Field Theory July 14-19 2008 Williamsburg, Virginia, USA

We study the equation of state in two-flavor QCD at finite temperature and density. Simulations are made with the RG-improved gluon action and the clover-improved Wilson quark action. Along the lines of constant physics for mPS/mV = 0.65 and 0.80, we compute the derivatives of the quark determinant with respect to the quark chemical potential μq up to the fourth order at μq = 0. We adopt several improvement techniques in the evaluation. We study thermodynamic quantities and quark number susceptibilities at finite μq using these derivatives. We find enhancement of the quark number susceptibility at finite μq, in accordance with previous observations using staggered-type quarks. This suggests the existence of a nearby critical point., The XXVI Internaitonal Symposium on Lattice Field Theory July 14-19 2008 Williamsburg, Virginia, USA

We study a reweighting method aiming at numerical studies of QCD at finite density, in which the conventional Monte-Carlo method cannot be applied directly. One of the most important problems in the reweighting method is the overlap problem. To solve it, we propose to perform simulations at several simulation points and combine their results in the data analyses. In this report, we introduce this multipoint reweighting method and test if the method works well by measuring histograms of physical quantities. Using this method, we calculate the meson masses as continuous functions of the gauge coupling beta and the hopping parameters kappa in QCD at zero density. We then determine lines of constant physics in the (beta, kappa) space and evaluate the derivatives of the lattice spacing with respect to beta and kappa along the lines of constant physics (inverse of the beta functions), which are needed in a calculation of the equation of state., 7 pages, 9 figures, talk presented at the 32nd International Symposium on Lattice Field Theory - Lattice 2014, June 23-28, 2014, Columbia University New York, NY

The reweighting method is widely used in numerical studies of QCD, in particular, for the cases in which the conventional Monte-Carlo method cannot be applied directly, e.g., finite density QCD. However, the application range of the reweighing method is restricted due to several problems. One of the most severe problems here is the overlap problem. To solve it, we examine a multipoint reweighting method in which simulations at several simulation points are combined in the data analyses. We systematically study the applicability and limitation of the multipoint reweighting method in two-flavor QCD at zero density. Measuring histograms of physical quantities at a series of simulation points, we apply the multipoint reweighting method to calculate the meson masses as continuous functions of the gauge coupling $\beta$ and the hopping parameters $\kappa$. We then determine lines of constant physics and beta functions, which are needed in a calculation of the equation of state at finite temperature., Comment: 16 pages, 25 figures. arXiv admin note: text overlap with arXiv:1501.06331

We present results for mesonic propagators in temporal and spatial direction and for topological properties at T below and above the deconfining transition in quenched QCD. We use anisotropic lattices and Wilson fermions., Comment: 6 pages, 7 figures, Talk given at 16th International Symposium on Lattice Field Theory (LATTICE 98(hightemp)) , Boulder, CO, 13-18 Jul 1998. (Replaced: Fig.4 corrected, further minor modifications in legends and text.)

論文(Article)

論文(Article)

We present results on the light hadron spectrum and quark mass in two-flavor QCD calculated with small sea quark masses down to $m_{PS}/m_{V}=0.35$. The configurations are generated using the RG improved gauge and tadpole-improved clover quark action at $\beta=1.8$, where $a^{-1} \simeq 1$ GeV. Chiral extrapolations are made using not only polynomials and ChPT in the continuum but also formulae of Wilson chiral perturbation theory (WChPT) including $O(a^2)$ chiral breaking terms. We examine the viability of WChPT and its influence on quark masses., Comment: 3 pages, 3 figures, Talk presented at Lattice2004(spectrum), Fermilab, June 21-26, 2004

We study the phase structure of QCD at high temperature and density by lattice QCD simulations adopting a histogram method. We try to solve the problems which arise in the numerical study of the finite density QCD, focusing on the probability distribution function (histogram). As a first step, we investigate the quark mass dependence and the chemical potential dependence of the probability distribution function as a function of the Polyakov loop when all quark masses are sufficiently large, and study the properties of the distribution function. The effect from the complex phase of the quark determinant is estimated explicitly. The shape of the distribution function changes with the quark mass and the chemical potential. Through the shape of the distribution, the critical surface which separates the first order transition and crossover regions in the heavy quark region is determined for the 2+1-flavor case., 7 pages, 12 figures, proceedings of the 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australia

We report the first observation of stable single photon sources in silicon carbide (SiC). These sources are extremely bright and operate at room temperature demonstrating that SiC is a viable material in which to realize various quantum information, computation and photonic applications. The maximum single photon count rate detected is 700k counts/s with an inferred quantum efficiency around 70%. The single photon sources are due to intrinsic deep level defects constituted of carbon antisite-vacancy pairs. These are shown to be formed controllably by electron irradiation. The variability of the temporal kinetics of these single defects is investigated in detail., 8 pages + 3 pages (supplementary)

We study thermodynamic properties of 2+1 flavor QCD with improved Wilson quarks coupled with the RG improved Iwasaki glue, using the fixed scale approach. We present the results for the equation of state, renormalized Polyakov loop, and chiral condensate., Comment: 7 pages, 7 figures, proceedings of the 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australia

We extend our previous study of the QCD phase structure in the heavy quark region to non-zero chemical potentials. To identify the critical point where the first order deconfining transition terminates, we study an effective potential defined by the probability distribution function of the plaquette and the Polyakov loop. The reweighting technique is shown to be powerful in evaluating the effective potential in a wide range of the plaquette and Polyakov loop expectation values. We adopt the cumulant expansion to overcome the sign problem in the calculation of complex phase of the quark determinant. We find that the method provides us with an intuitive and powerful way to study the phase structure. We estimate the location of the critical point at finite chemical potential in the heavy quark region., Comment: 7 pages, 7 figures; XXIX International Symposium on Lattice Field Theory - Lattice 2011

It is shown that a series of solvable polynomials is attached to the series of zero modes constructed by Adam, Muratori and Nash \cite{AdamMuratoriNash1, Comment: 13 pages

We study the quark mass dependence of the finite temperature QCD phase transition in the heavy quark region using an effective potential defined through the probability distribution function of the average plaquette. Performing a simulation of SU(3) pure gauge theory, we first confirm that the distribution function has two peaks indicating that the phase transition is of first order in the heavy quark limit, while the first order transition turns into a crossover as the quark mass decreases from infinity, where the mass dependence of the distribution function is evaluated by the reweighting method combined with the hopping parameter expansion. We determine the endpoint of the first order transition region for N_f=1, 2, 3 and 2+1 cases. The quark mass dependence of the latent heat is also evaluated in the first order transition region., Comment: 13 pages, 17 figures, 3 tables

We study scaling behavior of a chiral order parameter performing a simulation of two-flavor QCD with improved Wilson quarks. It has been shown that the scaling behavior of the chiral order parameter defined by a Ward-Takahashi identity agrees with the scaling function of the three-dimensional O(4) spin model at zero chemical potential. We extend the scaling study to finite density QCD. Calculating derivatives of the chiral order parameter with respect to the chemical potential in two-flavor QCD, the scaling property of chiral phase transition is discussed in the low density region. We moreover calculate the curvature of the phase boundary of the chirl phase transition in the temperature and chemical potential plane assuming the O(4) scaling relation., Comment: 7 pages, 6 figures, poster presented at the XXVIII International Symposium on Lattice Field Theory, June 14-19 2010, Villasimius, Italy

Dirac-Sobolev and Dirac-Hardy inequalities in $L^1$ are established in which the $L^p$ spaces which feature in the classical Sobolev and Hardy inequalities are replaced by weak $L^p$ spaces. Counter examples to the analogues of the classical inequalities are shown to be provided by zero modes for appropriate Pauli operators constructed by Loss and Yau., Comment: 11 pages. To appear in Publ. RIMS, Kyoto University

We propose a new approach to finite density QCD based on a histogram method with phase quenched simulations at finite chemical potential. Integrating numerically the derivatives of the logarithm of the quark determinant with respect to the chemical potential, we calculate the reweighting factor and the complex phase of the quark determinant. The complex phase is handled with a cumulant expansion to avoid the sign problem. We examine the applicability of this method., Comment: 7 pages, 11 figures

We study the quark mass dependence of the QCD phase transition by an effective potential defined through the distribution function of observables. As a test of the method, we study the first order deconfinement phase transition in the heavy quark mass limit and its fate at lighter quark masses. We confirm that the distribution function for the plaquette has two peaks indicating that the phase transition is of first order in the heavy quark limit. We then study the quark mass dependence of the distribution function by a reweighting method combined with the hopping parameter expansion. We find that the first order transition turns into a crossover as the quark mass decreases. We determine the critical point for the cases of $N_f$=1, 2, 3 and 2+1. We find that the probability distribution function provides us with a powerful tool to study the order of transitions., 7 pages, 7 figure, Talk presented at the XXVIII International Symposium on Lattice Field Theory, Lattice2010, Villasimius, Italy, June 2010

We present the status of our study on the equation of state in 2+1 flavor QCD with non-perturbatively improved Wilson quarks coupled with the RG improved glue. We apply the T-integration method to non-perturbatively calculate the equation of state by the fixed-scale approach., Comment: 7 pages, 7 figures, talk presented at the XXVIII International Symposium on Lattice Field Theory, June 14-19 2010, Villasimius, Italy

The free energy between a static quark and an antiquark is studied by using the color-singlet Polyakov-line correlation at finite temperature. We perform simulations on $32^3 \times 12$, 10, 8, 6, 4 lattices in the high temperature phase with the RG-improved gluon action and 2+1 flavors of the clover-improved Wilson quark action. Since the simulations are based on the fixed scale approach that the temperature can be varied without changing the spatial volume and renormalization factor, it is possible to investigate temperature dependence of the heavy-quark free energy without any adjustment of the overall constant. We find that, the heavy-quark free energies at short distance converge to the heavy-quark potential evaluated from the Wilson-loop operator at zero temperature, in accordance with the expected insensitivity of short distance physics to the temperature. At long distance, the heavy-quark free energies approach to twice the single-quark free energies, implying that the interaction between heavy quarks is screened. The Debye screening mass obtained from the long range behavior of the heavy-quark free energy is compared with results of the thermal perturbation theory and those of $N_f=2$ and $N_f=0$ lattice simulations., To appear in the proceedigns of 27th International Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 25-31 July 2009

Nonlinear evolution of circularly polarized Alfv\'en waves are discussed by using the recently developed Vlasov-MHD code, which is a generalized Landau-fluid model. The numerical results indicate that as far as the nonlinearity in the system is not so large, the Vlasov-MHD model can validly solve time evolution of the Alfv\'enic turbulence both in the linear and nonlinear stages. The present Vlasov-MHD model is proper to discuss the solar coronal heating and solar wind acceleration by Alfve\'n waves propagating from the photosphere., Comment: submitted to Planetary and Space Science

We study thermodynamics of SU(3) gauge theory at fixed scales on the lattice, where we vary temperature by changing the temporal lattice size N_t=(Ta_t)^{-1}. In the fixed scale approach, finite temperature simulations are performed on common lattice spacings and spatial volumes. Consequently, we can isolate thermal effects in observables from other uncertainties, such as lattice artifact, renormalization factor, and spatial volume effect. Furthermore, in the EOS calculations, the fixed scale approach is able to reduce computational costs for zero temperature subtraction and parameter search to find lines of constant physics, which are demanding in full QCD simulations. As a test of the approach, we study the thermodynamics of the SU(3) gauge theory on isotropic and anisotropic lattices. In addition to the equation of state, we calculate the critical temperature and the static quark free energy at a fixed scale., 7pages, 3figures, proceedings of Lattice 2008, Williamsburg, Virginia, USA, July 14-19, 2008

Screening properties of the quark gluon plasma are studied from Polyakov-loop correlation in lattice QCD simulations with two flavors of improved Wilson quarks at temperatures $T/\Tpc \simeq 1$--4 where $\Tpc$ is the pseudocritical temperature. Using the Euclidean-time reflection symmetry and the charge conjugation symmetry, we introduce various types of Polyakov-loop correlation functions and extract screening masses in magnetic and electric sectors. We find that the temperature dependence of the screening masses are well described by the weak coupling expansion. We also find that a ratio of the screening masses in the electric sector to the magnetic sector shows qualitative agreement with a prediction from the dimensionally-reduced effective field theory and the N=4 supersymmetric Yang-Mills theory at $1.3 < T/\Tpc < 3$., 7 pages, 5 figures, Talk given at the XXVI International Symposium on Lattice Field Theory (LATTICE 2008), July 14-19, 2008, Williamsburg, Virginia, USA

We study the finite temperature transition in QCD with three flavors of equal masses using the R and RHMC algorithm on lattices with temporal extent N_{\tau}=4 and 6. For the transition temperature in the continuum limit we find r_0 T_c=0.429(8) for the light pseudo-scalar mass corresponding to the end point of the 1st order transition region. When comparing the results obtained with the R and RHMC algorithms for p4fat3 action we see no significant step-size errors down to a lightest pseudo-scalar mass of m_{ps} r_0=0.4., Comment: 13 pages, RevTeX, 10 figures

Renormalization constants ($Z$-factors) of vector and axial-vector currents are determined non-perturbatively in quenched QCD for a renormalization group improved gauge action and a tadpole improved clover quark action using the Schr\"odinger functional method. Non-perturbative values of $Z$-factors turn out to be smaller than one-loop perturbative values by $O(15%)$ at lattice spacing of $a^{-1}\approx$ 1 GeV. The pseudoscalar and vector meson decay constants calculated with the non-perturbative $Z$-factors show a much better scaling behavior compared to previous results obtained with tadpole improved one-loop $Z$-factors. In particular, the non-perturbative $Z$-factors normalized at infinite physical volume show that scaling violation of the decay constants are within about 10% up to the lattice spacing $a^{-1}\sim 1$ GeV. The continuum estimates obtained from data in the range $a^{-1}=$ 1 -- 2 GeV agree with those determined from finer lattices ($a^{-1}\sim 2-4$ GeV) with the standard action., Comment: 19 pages, 18 eps figures. Corrected address

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to $m_{PS}/m_{V}=0.60$--0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at $\beta=1.8$ ($a = 0.2$ fm from $\rho$ meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of $m_{PS}/m_{V}=0.80$--0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fails, the Wilson ChPT (WChPT) that includes $a^2$ effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as $m_{PS}/m_V \simgt 0.5$. Reanalyzing the previous data %at $m_{PS}/m_{V}=0.80$--0.55 with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, $m_{ud}^{\bar{\rm MS}}(\mu=2 {GeV}) = 3.11(17)$ [MeV] in the continuum limit., Comment: 33 pages

We report on our study of two-flavor full QCD on anisotropic lattices using $O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge and quark anisotropies corresponding to the renormalized anisotropy $\xi=a_s/a_t = 2$ are determined as functions of $\beta$ and $\kappa$, which covers the region of spatial lattice spacings $a_s\approx 0.28$--0.16 fm and $m_{PS}/m_V\approx 0.6$--0.9. The calibrations of the bare anisotropies are performed with the Wilson loop and the meson dispersion relation at 4 lattice cutoffs and 5--6 quark masses. Using the calibration results we calculate the meson mass spectrum and the Sommer scale $r_0$. We confirm that the values of $r_0$ calculated for the calibration using pseudo scalar and vector meson energy momentum dispersion relation coincide in the continuum limit within errors. This work serves to lay ground toward studies of heavy quark systems and thermodynamics of QCD including the extraction of the equation of state in the continuum limit using Wilson-type quark actions., Comment: 16 pages, 23 figures, Version accepted for publication in Physical Review D

We explore the region of small sea quark masses below $m_{PS}/m_V=0.5$ in two-flavor QCD using a mean-field improved clover quark action and an RG-improved gauge action at $a \simeq 0.2$ fm on $12^3 \times 24$ and $16^3 \times 24$ lattices. We find that instability of the standard BiCGStab algorithm at small quark masses can be mostly removed by the BiCGStab(DS-$L$) algorithm, which employs $L$-th minimal residual polynomials with a dynamical selection of $L$. We also find singular spikes of $\Delta H$ in the HMC algorithm at moderate values of $\Delta\tau$. Nature of the spike is studied. We also study finite-size effects and chiral properties of meson masses., Comment: 3 pages, 4 figures, Lattice2002(spectrum)

The non-perturbative $\csw$ determined by the Schr\"{o}dinger functional (SF) method with the RG-improved gauge action in dynamical $N_f=3$ QCD shows a finite volume effect when the numerical simulations are carried out at a constant lattice size $L/a$. We remove the unwanted finite volume effect by keeping physical lattice extent $L$ at a constant. The details of the method and the result obtained for non-perturbative $\csw$ with a constant $L$ are reported., Comment: Lattice 2003 (improve), 3 pages, 3 figures

We present results for the mass of the etaprime meson for two-flavor lattice QCD in the continuum limit, calculated on the CP-PACS computer, using an RG-improved gauge action and clover fermion action with tadpole-improved csw. Measurements are made at three couplings corresponding to a approx. 0.22, 0.16, 0.11 fm for four quark masses corresponding to mpi over mrho approx. 0.8, 0.75, 0.7, 0.6. Thw two-loop diagrams are evaluated using a noisy source method. Quark smearing for both one- and two- loop diagrams is successfully applied to obtain ground state signals in the etaprime channel. We obtain metaprime=0.960(87)+0.036-0.286GeV in the continuum limit, where the second error represents the systematic uncertainty coming from varying the functional form for chiral and continuum extrapolations., 3 pages, 6 figures

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., Lattice2001(heavyquark), 3 pages

We study the response of the heavy-light meson mass to the chemical potential ($\partial{m}/\partial{\mu}$) at high temperature and at zero chemical potential. Preliminary results show that $\partial{m}/\partial{\mu}|_{\mu=0}$ is negative in the confinement phase and is positive in the deconfinement phase. This may suggest the possibility for the suppression of $J/\psi$ without the quark gluon plasma formation. We study the response of meson masses to the chemical potential ($\partial{m}/\partial{\mu}$) 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 $\partial{m}/\partial{\mu}|_{\mu=0}$ is negative in the confinement phase and positive in the deconfinement phase.