arXiv subjects

T. Yoshié

Publications and source records attributed to T. Yoshié.

At least 19 recordsLinked to original sources

arXiv2018

Calculation of $K \to ππ$ decay amplitudes with an improved Wilson fermion action in a nonzero momentum frame in lattice QCD

We present our result for the $K\toππ$ decay amplitudes for both the $ΔI=1/2$ and $3/2$ processes with the improved Wilson fermion action. In order to realize the physical kinematics, where the pions in the final state have finite momenta, we consider the decay process $K({\bf p}) \to π({\bf p}) + π({\bf 0})$ in the nonzero momentum frame with momentum ${\bf p}=(0,0,2π/L)$ on the lattice. Our calculations are carried out with $N_f=2+1$ gauge configurations generated with the Iwasaki gauge action and nonperturbatively $O(a)$-improved Wilson fermion action at $a=0.091\,{\rm fm}$ ($1/a=2.176\,{\rm GeV}$), $m_π=260\,{\rm MeV}$, and $m_K=570\,{\rm MeV}$ on a $48^3\times 64$ ($La=4.4\,{\rm fm}$) lattice. For these parameters the energy of the $K$ meson is set at that of two-pion in the final state. We obtain ${\rm Re}A_2 = 2.431(19) \times10^{ -8}\,{\rm GeV}$, ${\rm Re}A_0 = 51(28) \times10^{ -8}\,{\rm GeV}$, and $ε'/ε= 1.9(5.7) \times10^{-3}$ for a matching scale $q^* =1/a$ where the errors are statistical. The dependence on the matching scale $q^*$ of these values is weak. The systematic error arising from the renormalization factors is expected to be around $1.3\%$ for ${\rm Re}A_2$ and $11 \%$ for ${\rm Re}A_0$. Prospects toward calculations with the physical quark mass are discussed.

hep-lat↗

arXiv2015

Mass and Axial current renormalization in the Schrödinger functional scheme for the RG-improved gauge and the stout smeared $O(a)$-improved Wilson quark actions

We present the quark mass and axial current renormalization factors for the RG-improved Iwasaki gauge action and three flavors of the stout smeared $O(a)$-improved Wilson quark action. We employ $α=0.1$ and $n_{\mathrm{step}}=6$ for the stout link smearing parameters and all links in the quark action are replaced with the smeared links. Using the Schrödinger functional scheme we evaluate the renormalization factors at $β=1.82$ where large scale simulations are being carried out.

hep-lat↗

arXiv2015

Calculation of $K \to ππ$ decay amplitudes with improved Wilson fermion action in lattice QCD

We present our result for the $K\toππ$ decay amplitudes for both the $ΔI=1/2$ and $3/2$ processes with the improved Wilson fermion action. Expanding on the earlier works by Bernard {\it et al.} and by Donini {\it et al.}, we show that mixings with four-fermion operators with wrong chirality are absent even for the Wilson fermion action for the parity odd process in both channels due to CPS symmetry. Therefore, after subtraction of an effect from the lower dimensional operator, a calculation of the decay amplitudes is possible without complications from operators with wrong chirality, as for the case with chirally symmetric lattice actions. As a first step to verify the possibility of calculations with the Wilson fermion action, we consider the decay amplitudes at an unphysical quark mass $m_K \sim 2 m_π$. Our calculations are carried out with $N_f=2+1$ gauge configurations generated with the Iwasaki gauge action and nonperturbatively $O(a)$-improved Wilson fermion action at $a=0.091\,{\rm fm}$, $m_π=280\,{\rm MeV}$, and $m_K=580\,{\rm MeV}$ on a $32^3\times 64$ ($La=2.9\,{\rm fm}$) lattice. For the quark loops in the penguin and disconnected contributions in the $I=0$ channel, the combined hopping parameter expansion and truncated solver method work very well for variance reduction. We obtain, for the first time with a Wilson-type fermion action, that ${\rm Re}A_0 = 60(36) \times10^{ -8}\,{\rm GeV}$ and ${\rm Im}A_0 =-67(56) \times10^{-12}\,{\rm GeV}$ for a matching scale $q^* =1/a$. The dependence on the matching scale $q^*$ for these values is weak.

hep-lat↗

arXiv2014

Calculation of $K \to ππ$ decay amplitudes with improved Wilson fermion in 2+1 flavor lattice QCD

We present results for the $K\toππ$ decay amplitudes for both the $ΔI=1/2$ and $3/2$ channels. This calculation is carried out on 480 gauge configurations in $N_f=2+1$ QCD generated over 12,000 trajectories with the Iwasaki gauge action and non-perturbatively $O(a)$-improved Wilson fermion action at $a=0.091\,{\rm fm}$, $m_π=280\,{\rm MeV}$ and $m_K=580\,{\rm MeV}$ on a $32^3\times 64$ ($La=2.9\,{\rm fm}$) lattice. For the quark loops in the Penguin and disconnected contributions in the $I=0$ channel, the combined hopping parameter expansion and truncated solver techniques work very well for variance reduction. We obtain, for the first time with a Wilson-type fermion action, that ${\rm Re}A_0 = 60(36) \times10^{ -8}\,{\rm GeV}$ and ${\rm Im}A_0 =-67(56) \times10^{-12}\,{\rm GeV}$ for a matching scale $q^* =1/a$. The dependence on the matching scale is weak.

hep-lat↗

arXiv2013

Calculation of $K \to ππ$ decay amplitudes with improved Wilson fermion

We present results of our trial calculation of the $K \to ππ$ decay amplitudes with the improved Wilson fermion action. Calculations are carried out with $N_f=2+1$ gauge configurations generated with the Iwasaki gauge action and non-perturbatively $O(a)$-improved Wilson fermion action at $a=0.091\,{\rm fm}$, $m_π=280\,{\rm MeV}$ and $m_K=560\,{\rm MeV} (\sim 2 m_π)$ on a $32^3\times 64$ ($La=2.9 {\rm fm}$) lattice.

hep-lat↗

arXiv2013

Charmed baryons at the physical point in 2+1 flavor lattice QCD

We investigate the charmed baryon mass spectrum using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are tuned to their physical values, reweighted from those employed in the configuration generation. At the physical point, the inverse lattice spacing determined from the $Ω$ baryon mass gives $a^{-1}=2.194(10)$ GeV, and thus the spatial extent becomes $L = 32 a = 2.88(1)$ fm. Our results for the charmed baryon masses are consistent with experimental values, except for the mass of $Ξ_{cc}$, which has been measured by only one experimental group so far and has not been confirmed yet by others. In addition, we report values of other doubly and triply charmed baryon masses, which have never been measured experimentally.

hep-lat↗

arXiv2011

$ρ$ Meson Decay in 2+1 Flavor Lattice QCD

We perform a lattice QCD study of the $ρ$ meson decay from the $N_f=2+1$ full QCD configurations generated with a renormalization group improved gauge action and a non-perturbatively $O(a)$-improved Wilson fermion action. The resonance parameters, the effective $ρ\toππ$ coupling constant and the resonance mass, are estimated from the $P$-wave scattering phase shift for the isospin I=1 two-pion system. The finite size formulas are employed to calculate the phase shift from the energy on the lattice. Our calculations are carried out at two quark masses, $m_π=410\,{\rm MeV}$ ($m_π/m_ρ=0.46$) and $m_π=300\,{\rm MeV}$ ($m_π/m_ρ=0.35$), on a $32^3\times 64$ ($La=2.9\,{\rm fm}$) lattice at the lattice spacing $a=0.091\,{\rm fm}$. We compare our results at these two quark masses with those given in the previous works using $N_f=2$ full QCD configurations and the experiment.

hep-lat↗

arXiv2011

Charm quark system at the physical point of 2+1 flavor lattice QCD

We investigate the charm quark system using the relativistic heavy quark action on 2+1 flavor PACS-CS configurations previously generated on $32^3 \times 64$ lattice. The dynamical up-down and strange quark masses are set to the physical values by using the technique of reweighting to shift the quark hopping parameters from the values employed in the configuration generation. At the physical point, the lattice spacing equals $a^{-1}=2.194(10)$ GeV and the spatial extent $L=2.88(1)$ fm. The charm quark mass is determined by the spin-averaged mass of the 1S charmonium state, from which we obtain $m_{\rm charm}^{\msbar}(μ= m_{\rm charm}^{\msbar}) = 1.260(1)(6)(35)$ GeV, where the errors are due to our statistics, scale determination and renormalization factor. An additional systematic error from the heavy quark is of order $α_s^2 f(m_Q a)(a Λ_{QCD})$, which is estimated to be a percent level if the factor $f(m_Q a)$ analytic in $m_Q a$ is of order unity. Our results for the charmed and charmed-strange meson decay constants are $f_D=226(6)(1)(5)$ MeV, $f_{D_s}=257(2)(1)(5)$ MeV, again up to the heavy quark errors of order $α_s^2 f(m_Q a)(a Λ_{QCD})$. Combined with the CLEO values for the leptonic decay widths, these values yield $|V_{cd}| = 0.205(6)(1)(5)(9)$, $|V_{cs}| = 1.00(1)(1)(3)(3)$, where the last error is on account of the experimental uncertainty of the decay widths.

hep-lat↗

arXiv2010

Calculation of $ρ$ meson decay width from the PACS-CS configurations

We present preliminary results on the $ρ$ meson decay width from $N_f=2+1$ full QCD configurations generated by PACS-CS Collaboration. The decay width is estimated from the $P$-wave scattering phase shift for the isospin $I=1$ two-pion system. The finite size formula presented by Lüscher in the center of mass frame and its extension to non-zero total momentum frame by Rummukainen and Gottlieb are employed for the calculations of the phase shift. Our calculations are carried out at $m_π=410\ {\rm MeV}$ ($m_π/m_ρ=0.46$) and $a=0.091\ {\rm fm}$ on a $32^3\times 64$ ($La=2.9 {\rm fm}$) lattice.

hep-lat↗

arXiv2010

Non-perturbative renormalization of quark mass in Nf=2+1 QCD with the Schroedinger functional scheme

We present an evaluation of the quark mass renormalization factor for Nf=2+1 QCD. The Schroedinger functional scheme is employed as the intermediate scheme to carry out non-perturbative running from the low energy region, where renormalization of bare mass is performed on the lattice, to deep in the high energy perturbative region, where the conversion to the renormalization group invariant mass or the MS-bar scheme is safely carried out. For numerical simulations we adopted the Iwasaki gauge action and non-perturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy regions and three lattice spacings to take the continuum limit at each scale. The regularization independent step scaling function of the quark mass for the Nf=2+1 QCD is obtained in the continuum limit. Renormalization factors for the pseudo scalar density and the axial vector current are also evaluated for the same action and the bare couplings as two recent large scale Nf=2+1 simulations; previous work of the CP-PACS/JLQCD collaboration, which covered the up-down quark mass range heavier than $m_π\sim 500$ MeV and that of PACS-CS collaboration for much lighter quark masses down to $m_π=155$ MeV. The quark mass renormalization factor is used to renormalize bare PCAC masses in these simulations.

hep-lat↗

arXiv2009

Precise determination of the strong coupling constant in Nf=2+1 lattice QCD with the Schrödinger functional scheme

We present an evaluation of the running coupling constant for Nf=2+1 QCD. The Schroedinger functional scheme is used as the intermediate scheme to carry out non-perturbative running from the low energy region, where physical scale is introduced, to deep in the high energy perturbative region, where conversion to the MS-bar scheme is safely performed. Possible systematic errors due to the use of perturbation theory occur only in the conversion from three-flavor to four-flavor running coupling constant near the charm mass threshold, where higher order terms beyond 5th order in the $β$ function may not be negligible. For numerical simulations we adopted Iwasaki gauge action and non-perturbatively improved Wilson fermion action with the clover term. Seven renormalization scales are used to cover from low to high energy region and three lattice spacings to take the continuum limit at each scale. A physical scale is introduced from the previous Nf=2+1 simulation of the CP-PACS/JL-QCD collaboration, which covered the up-down quark mass range heavier than $m_π\sim 500$ MeV.

hep-lat↗

arXiv2008

Light quark masses from unquenched lattice QCD

We calculate the light meson spectrum and the light quark masses by lattice QCD simulation, treating all light quarks dynamically and employing the Iwasaki gluon action and the nonperturbatively O(a)-improved Wilson quark action. The calculations are made at the squared lattice spacings at an equal distance a^2~0.005, 0.01 and 0.015 fm^2, and the continuum limit is taken assuming an O(a^2) discretization error. The light meson spectrum is consistent with experiment. The up, down and strange quark masses in the \bar{MS} scheme at 2 GeV are \bar{m}=(m_{u}+m_{d})/2=3.55^{+0.65}_{-0.28} MeV and m_s=90.1^{+17.2}_{-6.1} MeV where the error includes statistical and all systematic errors added in quadrature. These values contain the previous estimates obtained with the dynamical u and d quarks within the error.

hep-lat↗

arXiv2007

Lattice QCD Calculation of the $ρ$ Meson Decay Width

We present a lattice QCD calculation of the $ρ$ meson decay width via the $P$-wave scattering phase shift for the I=1 two-pion system. Our calculation uses full QCD gauge configurations for $N_f=2$ flavors generated using a renormalization group improved gauge action and an improved Wilson fermion action on a $12^3\times24$ lattice at $m_π/m_ρ=0.41$ and the lattice spacing $1/a=0.92 {\rm GeV}$. The phase shift calculated with the use of the finite size formula for the two-pion system in the moving frame shows a behavior consistent with the existence of a resonance at a mass close to the vector meson mass obtained in spectroscopy. The decay width estimated from the phase shift is consistent with the experiment, when the quark mass is scaled to the realistic value.

hep-lat↗

arXiv2007

2+1 flavor light hadron spectrum and quark masses with the O(a) improved Wilson-clover quark formalism

We present a summary of results of the joint CP-PACS and JLQCD project toward a 2+1 flavor full QCD simulation with the O(a)-improved Wilson quark formalism and the Iwasaki gauge action. Configurations were generated during 2002-2005 at three lattice spacings, a~0.076, 0.100 and 0.122 fm, keeping the physical volume constant at (2.0fm)^3. Up and down quark masses are taken in the range m_{PS}/m_V~0.6-0.78. We have completed the analysis for the light meson spectrum and quark masses in the continuum limit using the full configuration set. The predicted meson masses reproduce experimental values in the continuum limit at a 1% level. The average up and down, and strange quark masses turn out to be m_{ud}^{\bar{MS}}(μ=2 GeV)=3.50(14)({}^{+26}_{-15}) MeV and m_s^{\bar{MS}}(μ=2 GeV)=91.8(3.9)({}^{+6.8}_{-4.1}) MeV. We discuss our future strategy toward definitive results on hadron spectroscopy with the Wilson-clover formalism.

hep-lat↗

arXiv2007

Neutron electric dipole moment with external electric field method in lattice QCD

We discuss a possibility that the Neutron Electric Dipole Moment (NEDM) can be calculated in lattice QCD simulations in the presence of the CP violating $θ$ term. In this paper we measure the energy difference between spin-up and spin-down states of the neutron in the presence of an uniform and static external electric field. We first test this method in quenched QCD with the RG improved gauge action on a $16^3\times 32$ lattice at $a^{-1}\simeq$ 2 GeV, employing two different lattice fermion formulations, the domain-wall fermion and the clover fermion for quarks, at relatively heavy quark mass $(m_{PS}/m_V \simeq 0.85)$. We obtain non-zero values of NEDM from calculations with both fermion formulations. We next consider some systematic uncertainties of our method for NEDM, using $24^3\times 32$ lattice at the same lattice spacing only with the clover fermion. We finally investigate the quark mass dependence of NEDM and observe a non-vanishing behavior of NEDM toward the chiral limit. We interpret this behavior as a manifestation of the pathology in the quenched approximation.

hep-lat↗

arXiv2006

$ρ$ meson decay from the lattice

We present preliminary results on the $ρ$ meson decay width estimated from the scattering phase shift of the I=1 two-pion system. The phase shift is calculated by the finite size formula for non-zero total momentum frame (the moving frame) derived by Rummukainen and Gottlieb, using the $N_f=2$ improved Wilson fermion action at $m_π/m_ρ=0.41$ and $L=2.53 {\rm fm}$.

hep-lat↗

arXiv2006

Calculation of Neutron EDM in quenched and full QCD

We report on a direct lattice calculation of the neutron EDM(NEDM) using the external electric field method in both quenched and full QCD. In quenched QCD, we use a $24^3\times 32$ lattice at $β=2.6$ with the Iwasaki gauge action and the clover fermion action to examine the viability of this method. In particular we investigate possible effects of violation of the periodic boundary condition of the external electric field on the NEDM signal. We also study the quark mass dependence of NEDM in quenched QCD, and observe that NEDM seems to remain non-zero toward the chiral limit because of the quenched artifact. In 2-flavor full QCD we employ configurations generated by the CP-PACS collaboration on a $24^3\times 48$ lattice at $β=2.1$ with the same gluon and quark actions as in the quenched case. Since the number of configurations is limited, we employ 8 different source points per one configuration and take an average over them. Our preliminary result at three quark masses ($m_{PS}/m_V\simeq 0.81, 0.76, 0.69$) indicates that non-zero value for NEDM can be obtained in full QCD. Statistical errors, however, are still too large to show the theoretically expected behaviour for NEDM in full QCD that it vanishes in the chiral limit.

hep-lat↗

arXiv2006

Nonperturbative $O(a)$ improvement of the Wilson quark action with the RG-improved gauge action using the Schrödinger functional method

We perform a nonperturbative determination of the $O(a)$-improvement coefficient $c_{\rm SW}$ and the critical hopping parameter $κ_c$ for $N_f$=3, 2, 0 flavor QCD with the RG-improved gauge action using the Schrödinger functional method. In order to interpolate $c_{\rm SW}$ and $κ_c$ as a function of the bare coupling, a wide range of $β$ from the weak coupling region to the moderately strong coupling points used in large-scale simulations is studied. Corrections at finite lattice size of $O(a/L)$ turned out to be large for the RG-improved gauge action, and hence we make the determination at a size fixed in physical units using a modified improvement condition. This enables us to avoid $O(a)$ scaling violations which would remain in physical observables if $c_{\rm SW}$ determined for a fixed lattice size $L/a$ is used in numerical simulations.

hep-lat↗