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Yusuke Taniguchi

Publications and source records attributed to Yusuke Taniguchi.

At least 19 recordsLinked to original sources
arXiv2024

Update of kaon semileptonic form factor using $N_f=2+1$ PACS10 configurations

We calculate the form factors for the kaon semileptonic decay process using the PACS10 configurations, whose physical volume is more than (10 fm)$^4$ very close to the physical point. The configurations were generated with the Iwasaki gauge action and $N_f=2+1$ stout-smeared nonperturbatively $O(a)$-improved Wilson quark action at the three lattice spacings, 0.085, 0.063, and 0.041 fm. We present updated results for the form factors, and discuss their continuum extrapolations, momentum transfer interpolation, and short chiral extrapolation to tune the simulated pion and kaon masses to the physical ones. From the results with various analyses, the systematic error of the form factor at the zero momentum transfer is estimated. The value of $|V_{us}|$ is determined using our result, and is compared with those using the previous calculations and also those determined through the kaon leptonic decay process.

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arXiv2023

$|V_{us}|$ from kaon semileptonic form factor in $N_f = 2+1$ QCD at the physical point on (10 fm)$^4$

We present a preliminary result of the kaon semileptonic form factor calculated at the smallest lattice spacing in the PACS10 configurations, whose physical volumes are more than (10 fm)$^4$ at the physical point. The configurations were generated using the Iwasaki gauge action and $N_f=2+1$ stout-smeared nonperturbatively $O(a)$ improved Wilson quark action at the three lattice spacings, 0.085, 0.063, and 0.041 fm. The value of $|V_{us}|$ in the continuum limit is estimated from our results including the preliminary one. We compare our result of $|V_{us}|$ with the previous results and those through the kaon leptonic decay.

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arXiv2022

Momentum transfer dependence of kaon semileptonic form factor on (10 fm)$^4$ at the physical point

We calculate the kaon semileptonic form factors using the two sets of the PACS10 configuration, whose physical volumes are more than (10 fm)$^4$ at the physical point. The lattice spacings are 0.063 and 0.085 fm. The configurations were generated using the Iwasaki gauge action and $N_f=2+1$ stout-smeared nonperturbatively $O(a)$-improved Wilson quark action. From the momentum transfer dependence of the form factors, we evaluate the slope and curvature for the form factors at the zero momentum transfer. Furthermore, we calculate the phase space factor, which is used to obtain $|V_{us}|$ through the kaon semileptonic decay. These results are compared with previous lattice results and experimental values.

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arXiv2022

$K_{\ell 3}$ form factors at the physical point: Toward the continuum limit

We present updated results for the form factors of the kaon semileptonic $(K_{\ell 3})$ decay process calculated with $N_f = 2 + 1$ nonperturbatively $O(a)$-improved Wilson quark action and Iwasaki gauge action at the physical point on large volumes of more than (10 fm)$^4$. In addition to our previous calculation at the lattice spacing $a = 0.085$ fm, we perform a calculation at the second lattice spacing of $0.063$ fm. Using the results for the form factors extracted from 3-point functions with the local and also conserved vector currents at the two lattice spacings, continuum extrapolation and interpolation of the momentum transfer are carried out simultaneously to obtain the value of the form factor $f_+(0)$ at the zero momentum transfer in the continuum limit. After investigation of stability of $f_+(0)$ against several fit forms and different data, we obtain $f_+(0) = 0.9615(10)(^{+47}_{\ -3})(5)$, where the first, second, and third errors are statistical, systematic errors from choice of the fit forms and isospin breaking effect, respectively. Combining our value of $f_+(0)$ and experimental input of the $K_{\ell 3}$ decay, one of the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{us}|$ is determined as $|V_{us}| = 0.2252(^{\ +5}_{-12})$, whose error contains the experimental one as well as that in the lattice calculation. This value is reasonably consistent with the ones determined from recent lattice QCD results of $f_+(0)$ and also the one determined through the kaon leptonic decay process. We observe some tension between our value and $|V_{us}|$ evaluated from the unitarity of the CKM matrix with $|V_{ud}|$, while it depends on the size of the error of $|V_{ud}|$. It is also found that $|V_{us}|$ determined with our phase space integrals through six $K_{\ell 3}$ decay processes is consistent with the above one using $f_+(0)$.

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arXiv2021

General purpose lattice QCD code set Bridge++ 2.0 for high performance computing

Bridge++ is a general-purpose code set for a numerical simulation of lattice QCD aiming at a readable, extensible, and portable code while keeping practically high performance. The previous version of Bridge++ is implemented in double precision with a fixed data layout. To exploit the high arithmetic capability of new processor architecture, we extend the Bridge++ code so that optimized code is available as a new branch, i.e., an alternative to the original code. This paper explains our strategy of implementation and displays application examples to the following architectures and systems: Intel AVX-512 on Xeon Phi Knights Landing, Arm A64FX-SVE on Fujitsu A64FX (Fugaku), NEC SX-Aurora TSUBASA, and GPU cluster with NVIDIA V100.

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arXiv2021

Calculation of kaon semileptonic form factor with the PACS10 configuration

We present preliminary results for the kaon semileptonic form factors using the PACS10 configurations, whose physical volume is more than (10 fm)$^3$ at the physical point with the lattice spacings of 0.085 and 0.064 fm. The configurations were generated using the Iwasaki gauge action and $N_f=2+1$ stout-smeared Clover quark action. For the continuum extrapolation, we calculate the form factors with the local and conserved vector currents. The form factors in the two lattice spacings are extrapolated to the continuum limit using a fit function based on the NLO SU(3) ChPT formula with terms corresponding to finite lattice spacing effects. The value of $|V_{us}|$ is determined using our preliminary result of the form factor at the zero momentum transfer in the continuum limit. The result is compared with recent lattice results, and also predictions of the standard model from the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix.

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arXiv2021

Latent heat and pressure gap at the first-order deconfining phase transition of SU(3) Yang-Mills theory using the small flow-time expansion method

We study the latent heat and the pressure gap between the hot and cold phases at the first-order transition temperature $T=T_c$ of SU(3) Yang-Mills theory, using the small flow-time expansion (SF$t$X) method based on the gradient flow. We first examine alternative procedures in the SFtX method -- the order of the continuum and vanishing flow-time extrapolations. We confirm that the final results adopting the two orders, as well as other alternatives in which the perturbative order of the matching coefficients and the renormalization scale of the flow scheme are varied, are all consistent with each other. We also confirm $\Delta p$ is consistent with zero, as expected from the dynamical balance of two phases at $T_c$. For the latent heat in the continuum limit, we find $\Delta \epsilon /T^4 = 1.117(40)$ for the spatial volume $L^3$ corresponding to the aspect ratio $N_s/N_t=T_cL=8$ and $1.349(38)$ for $N_s/N_t=6$. From hysteresis curves, we show that the entropy density in the hot phase is sensitive to the spatial volume, while that in the confined phase is insensitive.

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arXiv2020

Latent heat and pressure gap at the first-order deconfining phase transition of SU(3) Yang-Mills theory using the small flow-time expansion method

We study latent heat and the pressure gap between the hot and cold phases at the first-order deconfining phase transition temperature of the SU(3) Yang-Mills theory. Performing simulations on lattices with various spatial volumes and lattice spacings, we calculate the gaps of the energy density and pressure using the small flow-time expansion (SFtX) method. We find that the latent heat $\Delta \epsilon$ in the continuum limit is $\Delta \epsilon /T^4 = 1.117 \pm 0.040$ for the aspect ratio $N_s/N_t=8$ and $1.349 \pm 0.038$ for $N_s/N_t=6$ at the transition temperature $T=T_c$. We also confirm that the pressure gap is consistent with zero, as expected from the dynamical balance of two phases at $T_c$. From hysteresis curves of the energy density near $T_c$, we show that the energy density in the (metastable) deconfined phase is sensitive to the spatial volume, while that in the confined phase is insensitive. Furthermore, we examine the effect of alternative procedures in the SFtX method - the order of the continuum and the vanishing flow-time extrapolations, and also the renormalization scale and higher-order corrections in the matching coefficients. We confirm that the final results are all very consistent with each other for these alternatives.

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arXiv2020

Four quark operators for kaon bag parameter with gradient flow

To study the CP-violation using the $K_0-\bar{K}_0$ oscillation, we need the kaon bag parameter which represents QCD corrections in the leading Feynman diagrams. The lattice QCD provides us with the only way to evaluate the kaon bag parameter directly from the first principles of QCD. However, a calculation of relevant four quark operators with theoretically sound Wilson-type lattice quarks had to carry a numerically big burden of extra renormalizations and resolution of extra mixings due to the explicit chiral violation. Recently, the Small Flow-time eXpansion (SFtX) method was proposed as a general method based on the gradient flow to correctly calculate any renormalized observables on the lattice, irrespective of the explicit violations of related symmetries on the lattice. To apply the SFtX method, we need matching coefficients, which relate finite operators at small flow-times in the gradient flow scheme to renormalized observables in conventional renormalization schemes. In this paper, we calculate the matching coefficients for four quark operators and quark bi-linear operators, relevant to the kaon bag parameter.

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arXiv2020

Nf=2+1 QCD thermodynamics with gradient flow using two-loop matching coefficients

We study thermodynamic properties of Nf=2+1 QCD on the lattice adopting O(a)-improved Wilson quark action and Iwasaki gauge action. To cope with the problems due to explicit violation of the Poincare and chiral symmetries, we apply the Small Flow-time eXpansion (SFtX) method based on the gradient flow, which is a general method to correctly calculate any renormalized observables on the lattice. In this method, the matching coefficients in front of operators in the small flow-time expansion are calculated by perturbation theory. In a previous study using one-loop matching coefficients, we found that the SFtX method works well for the equation of state, chiral condensates and susceptibilities. In this paper, we study the effect of two-loop matching coefficients by Harlander et al. We also test the influence of the renormalization scale in the SFtX method. We find that, by adopting the mu_0 renormalization scale of Harlander et al. instead of the conventional mu_d=1/sqrt{8t} scale, the linear behavior at large t is improved so that we can perform the t -> 0 extrapolation of the SFtX method more confidently. In the calculation of the two-loop matching coefficients by Harlander et al., the equation of motion for quark fields was used. For the entropy density in which the equation of motion has no effects, we find that the results using the two-loop coefficients agree well with those using one-loop coefficients. On the other hand, for the trace anomaly which is affected by the equation of motion, we find discrepancies between the one- and two-loop results at high temperatures. By comparing the results of one-loop coefficients with and without using the equation of motion, the main origin of the discrepancies is suggested to be attributed to O((aT)^2)=O(1/N_t^2) discretization errors in the equation of motion at N_t =< 10.

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arXiv2020

$K_{l3}$ form factors in $N_f = 2+1$ QCD at physical point on large volume

We present our results of the $K_{l3}$ form factors on the volume whose spatial extent is more than $L=$10 fm, with the physical pion and kaon masses using the stout-smearing clover $N_f = 2+1$ quark action and Iwasaki gauge action at $a^{-1}\approx2.3$ GeV. The $K_{l3}$ form factor at zero momentum transfer is obtained from fit based on the next-to-leading (NLO) formula in SU(3) chiral perturbation theory. We estimate systematic errors of the form factor, mainly coming from the finite lattice spacing effect. We also determine the value of $|V_{us}|$ by combining our result with the experiment and check the consistency with the standard model prediction. The result is compared with the previous lattice calculations.

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arXiv2020

Calculation of PCAC mass with Wilson fermion using gradient flow

We calculate the PCAC mass for $(2+1)$ flavor full QCD with Wilson-type quarks. We adopt the Small Flow-time eXpansion (SFtX) method based on the gradient flow which provides us a general way to compute correctly renormalized observables even if the relevant symmetries for the observable are broken explicitly due to the lattice regularization, such as the Poinc\'{a}re and chiral symmetries. Our calculation is performed on heavy $u, d$ quarks mass ($m_{\pi}/m_{\rho}\simeq0.63$) and approximately physical $s$ quark mass with fine lattice $a \simeq 0.07$~fm. The results are compared with those computed with the Schr\"odinger functional method.

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arXiv2019

$K_{l3}$ form factors at the physical point on (10.9 fm)$^3$ volume

We present the calculation of the $K_{l3}$ form factors with $N_f = 2 + 1$ nonperturbatively $O(a)$-improved Wilson quark action and Iwasaki gauge action at the physical point on a large volume of (10.9 fm)$^3$ at one lattice spacing of $a = 0.085$ fm. We extract the form factors from 3-point functions with three different time separations between the source and sink operators to confirm suppression of excited state contributions. The form factors are calculated in very close to the zero momentum transfer, $q^2 = 0$, thanks to the large volume, so that stable interpolations to $q^2 = 0$ are carried out. Using our form factors, we obtain the form factor at $q^2 = 0$, $f_+(0) = 0.9603(16)(^{+14}_{\ -4})(44)(19)(1)$, where the first, second, and fifth errors are statistical, systematic errors from fit functions and the isospin breaking effect, respectively. The third and fourth errors denote the finite lattice spacing effects estimated from the renormalization factor and contribution beyond the leading order SU(3) chiral perturbation theory (ChPT). The result of $f_+(0)$ yields the Cabibbo-Kobayashi-Maskawa (CKM) matrix element, $|V_{us}| = 0.2255(13)(4)$, where the first error comes from our calculation and the second from the experiment. This value is consistent with the ones determined from the unitarity of the CKM matrix and the $K_{l2}$ decay within one standard deviation, while it is slightly larger than recent lattice calculations by at most 1.5 $\sigma$. Furthermore, we evaluate the shape of the form factors and the phase space integral from our results. We confirm that those results are consistent with the experiment, and also $|V_{us}|$ determined with our phase space integral agrees with the one in the above.

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arXiv2019

Determination of the endpoint of the first order deconfiniement phase transition in the heavy quark region of QCD

We study the endpoint of the first order deconfinement phase transition of 2 and 2+1 flavor QCD in the heavy quark region. We perform simulations of quenched QCD and apply the reweighting method to study the heavy quark region. The quark determinant for the reweighting is evaluated by a hopping parameter expansion. To reduce the overlap problem, we introduce an external source term of the Polyakov loop in the simulation. We study the location of critical point at which the first order phase transition changes to crossover by investigating the histogram of the Polyakov loop and applying the finite-size scaling analysis. We estimate the truncation error of the hopping parameter expansion, and discuss the lattice spacing dependence and the spatial volume dependence in the result of the critical point.

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arXiv2019

Study of 2+1 flavor finite-temperature QCD using improved Wilson quarks at the physical point with the gradient flow

We study thermodynamic properties of 2+1 flavor QCD applying the Small Flow-time eXpansion (SFtX) method based on the gradient flow. The method provides us with a general way to compute correctly renormalized observables irrespective of explicit violation of symmetries due to the regularization, such as the Poincare and chiral symmetries on the lattice. We report on the status of our on-going project to compute the energy-momentum tensor and the chiral condensate at the physical point with improved Wilson quarks, extending our previous study with slightly heavy u and d quarks. We also report on our test of two-loop matching coefficients recently calculated by Harlander et al., revisiting the case of QCD with slightly heavy u and d quarks. Our results suggest that the SFtX method is powerful in extracting physical observables on the lattice.

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arXiv2019

Measuring of chiral susceptibility using gradient flow

In lattice QCD with Wilson-type quarks, the chiral symmetry is explicitly broken by the Wilson term on finite lattices. Though the symmetry is guaranteed to recover in the continuum limit, a series of non-trivial procedures are required to recover the correct renormalized theory in the continuum limit. Recently, a new use of the gradient flow technique was proposed, in which correctly renormalized quantities are evaluated in the vanishing flow-time limit. This enables us to directly study the chiral condensate and its susceptibility with Wilson-type quarks. Extending our previous study of the chiral condensate and its disconnected susceptibility in (2+1)-flavor QCD at a heavy $u$, $d$ quark mass ($m_{\pi}/m_{\rho}\simeq0.63$) and approximately physical $s$ quark mass, we compute the connected contributions to the chiral susceptibility in the temperature range of 178--348 MeV on a fine lattice with $a\simeq0.07$ fm.

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arXiv2019

Study of energy-momentum tensor correlation function in $N_f=2+1$ full QCD for QGP viscosities

We study correlation functions of the energy-momentum tensor (EMT) in $(2+1)$-flavor full QCD to evaluate QGP viscosities. We adopt nonperturbatively improved Wilson fermion and Iwasaki gauge action. Our degenerate $u$, $d$ quark mass is rather heavy with $m_{\pi}/m_{\rho}\simeq0.63$, while the $s$ quark mass is set to approximately its physical value. Performing simulations on lattices with $N_t=16$ to 6 at a fine lattice spacing of $a=0.07$ fm, the temperature range of $T\simeq174$--$464$ MeV is covered using the fixed-scale approach. We attempt to compute viscosities by three steps: (1) calculate two point correlation functions of non-perturbatively renormalized EMT applying the gradient flow method, (2) derive the spectral function from correlation function, and (3) extract viscosities from the spectral function applying the Kubo formula. We report on the status of the project and present preliminary results for the shear viscosity in the high temperature phase.

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