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Ryoichiro Ueno

Publications and source records attributed to Ryoichiro Ueno.

5 recordsLinked to original sources
arXiv2020

Towards higher order numerical stochastic perturbation computation applied to the twisted Eguchi-Kawai model

We have evaluated perturbation coefficients of Wilson loops up to $O(g^8)$ for the four-dimensional twisted Eguchi-Kawai model using the numerical stochastic perturbation theory (NSPT) in arXiv:1902.09847. In this talk we present a progress report on the higher order calculation up to $O(g^{63})$, for which we apply a fast Fourier transformation (FFT) based convolution algorithm to the multiplication of polynomial matrices in the NSPT aiming for higher order calculation. We compare two implementations with the CPU-only version and the GPU version of the FFT based convolution algorithm, and find a factor 9 improvement on the computational speed of the NSPT algorithm with SU($N=225$) at $O(g^{31})$. The perturbation order dependence of the computational time, we investigate it up to $O(g^{63})$, shows a mild scaling behavior on the truncation order.

hep-lat↗
arXiv2019

Numerical stochastic perturbation theory applied to the twisted Eguchi-Kawai model

We present the results of an exploratory study of the numerical stochastic perturbation theory (NSPT) applied to the four dimensional twisted Eguchi-Kawai (TEK) model. We employ a Kramers type algorithm based on the Generalized Hybrid Molecular Dynamics (GHMD) algorithm. We have computed the perturbative expansion of square Wilson loops up to $O(g^8)$. The results of the first two coefficients (up to $O(g^4)$) have a high precision and match well with the exact values. The next two coefficients can be determined and even extrapolated to large $N$, where they should coincide with the corresponding coefficients for ordinary Yang-Mills theory on an infinite lattice. Our analysis shows the behaviour of the probability distribution for each coefficient tending to Gaussian for larger $N$. The results allow us to establish the requirements to extend this analysis to much higher order.

hep-lat↗
arXiv2018

Irregular parameter dependence of numerical results in tensor renormalization group analysis

We study the parameter dependence of numerical results obtained by the tensor renormalization group. We often observe an irregular behavior as the parameters are varied with the method, which makes it difficult to perform the numerical derivatives in terms of the parameter. With the use of two-dimensional Ising model we explicitly show that the sharp cutoff used in the truncated singular value decomposition causes this unwanted behavior when the level crossing happens between singular values below and above the truncation order as the parameters are varied. We also test a smooth cutoff, instead of the sharp one, as a truncation scheme and discuss its effects.

hep-lat↗
arXiv2017

Non-perturbative determination of the $Λ$-parameter in the pure SU(3) gauge theory from the twisted gradient flow coupling

We evaluate the $Λ$-parameter in the $\overline{\mathrm{MS}}$ scheme for the pure SU(3) gauge theory with the twisted gradient flow (TGF) method. A running coupling constant $g_{\mathrm{TGF}}^2(1/L)$ is defined in a finite volume box with size of $L^4$ with the twisted boundary condition. This defines the TGF scheme. Using the step scaling method for the TGF coupling with lattice simulations, we can evaluate the $Λ$-parameter non-perturbatively in the TGF scheme. In this paper we determine the dimensionless ratios, $Λ_{\mathrm{TGF}}/\sqrtσ$ and $r_{0}Λ_{\mathrm{TGF}}$ together with the $Λ$-parameter ratio $Λ_{\mathrm{SF}}/Λ_{\mathrm{TGF}}$ on the lattices numerically. Combined with the known ratio $Λ_{\overline{\mathrm{MS}}}/Λ_{\mathrm{SF}}$, we obtain $Λ_{\overline{\mathrm{MS}}}/\sqrtσ = 0.517(10)(^{+8}_{-7})$ and $r_{0}Λ_{\overline{\mathrm{MS}}}=0.593(12)(^{+12}_{-9})$, where the first error is statistical one and the second is our estimate of systematic uncertainty.

hep-lat↗