arXiv subjects

Asobu Suzuki

Publications and source records attributed to Asobu Suzuki.

6 recordsLinked to original sources

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.

hep-lat↗

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 Poincáre and chiral symmetries. Our calculation is performed on heavy $u, d$ quarks mass ($m_π/m_ρ\simeq0.63$) and approximately physical $s$ quark mass with fine lattice $a \simeq 0.07$~fm. The results are compared with those computed with the Schrödinger functional method.

hep-lat↗

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.

hep-lat↗

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 ($m_π/m_ρ\simeq0.63$) 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.

hep-lat↗

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 $m_π/m_ρ\simeq0.63$, 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.

hep-lat↗

arXiv2017

Energy-momentum tensor correlation function in Nf=2+1 full QCD at finite temperature

We measure correlation functions of the nonperturbatively renormalized energy-momentum tensor in $N_f=2+1$ full QCD at finite temperature by applying the gradient flow method both to the gauge and quark fields. Our main interest is to study the conservation law of the energy-momentum tensor and to test whether the linear response relation is properly realized for the entropy density. By using the linear response relation we calculate the specific heat from the correlation function. We adopt the nonperturbatively improved Wilson fermion and Iwasaki gauge action at a fine lattice spacing $=0.07$ fm. In this paper the temperature is limited to a single value $T=232$ MeV. The $u$, $d$ quark mass is rather heavy with $m_π/m_ρ=0.63$ while the $s$ quark mass is set to approximately its physical value.

hep-lat↗