Searcharxiv⌕ Search

arXiv subjects

Masato Nagatsuka

Publications and source records attributed to Masato Nagatsuka.

6 recordsLinked to original sources
arXiv2026

Recent update of nucleon axial-vector charge with the PACS10 superfine lattice

We update the results of the nucleon axial-vector charge with the third ensemble of the PACS10 gauge configurations, which are generated by the PACS Collaboration at the physical point with lattice volume larger than $(10\;{\rm fm})^4$ and three different lattice spacings, 0.085 fm (coarse), 0.063 fm (fine) and 0.041 fm (superfine). Although the results of the first two ensembles generated at the coarse and fine lattice spacings are published, our study using the third one generated at the superfine lattice spacing is still underway. In this work, the low-energy relations arising from the partially conserved axial-vector current (PCAC) relation are also examined in terms of the nucleon three-point functions to verify whether the lattice QCD data correctly reproduces the physics in the continuum within the statistical accuracy.

hep-lat↗
arXiv2025

Lattice study of scattering phase shifts for $DD^*$ and $BB^*$ systems using twisted boundary conditions: Search for bound state formation

We investigate the $S$- and $P$-wave phase shifts for the $DD^\ast$ and $BB^\ast$ scatterings using Lüscher's finite-size method under twisted boundary conditions to search for doubly charmed tetraquaks, $T_{cc}^+$, and doubly bottomed tetraquarks, $T_{bb}^-$ as the hadronic bound states. The $T_{cc}^+$ state was observed as a peak just bellow the $DD^*$ threshold by LHCb Collaboration, while the $T_{bb}^-$ state is a theoretically predicted tetraquark state having heavier quark flavors $bb\bar u \bar d$. Lüscher's finite-size method is one of the well established methods for calculating the scattering phase shifts between two hadrons in lattice QCD simulations. Several studies have used simulations under the periodic boundary condition to determine the scattering phase shifts at a few discrete momenta for the $DD^*$ system. However, the scattering phase shift has not been investigated for the $BB^*$ system. In this study, $S$- and $P$-wave scattering phase shifts for the $DD^*$ and $BB^*$ systems in both $I=0$ and $I=1$ channels under several types of partially twisted boundary conditions. The use of the partially twisted boundary conditions enables us to obtain the scattering phase shift at any momentum by continuously varying the twisting angle. It also allows us to easily access the $P$-wave scattering phase shifts through the mixing of $S$- and $P$-waves, which is induced by the imposed boundary conditions. The 2+1 flavor PACS-CS gauge ensembles at $m_π=295$, 411 and 569 MeV are used. For charm and bottom quarks, the relativistic heavy quark action is adopted to reduce the lattice discretization artifacts due to the heavy quark mass. We discuss the emergence of a shallow bound state with a binding energy of $O(100)$ keV at the physical pion mass in the $BB^*$ system, which has the quantum number $I(J^P)=0(1^+)$.

hep-lat↗
arXiv2025

Statistical repulsion on hyperons in two-color dense QCD

We investigate the onset of hyperons in baryonic (diquark) matter in two-color QCD (QC$_2$D) by introducing heavy quark doublets that emulate strange quarks. An even number of flavors is required to avoid the sign problem in lattice Monte Carlo simulations. To explore QC$_2$D matter containing both light and heavy quarks, we construct a model in which quarks interact with light-light, light-heavy (hyperonic), and heavy-heavy diquarks via Yukawa couplings. As the quark chemical potential increases, the light diquarks condense first and form baryonic matter, and this onset density can be understood in hadronic terms. In contrast, the onset density of hyperons is substantially higher than that estimated from the hadronic sector of the model. This shift reflects an effective repulsion among baryons induced by the pre-occupied light quarks. The Pauli blocking of light quarks suppresses the attractive diquark correlations responsible, in vacuum, for making hyperons lighter than the sum of the constituent light and heavy quark masses. Implications for three-color QCD are also briefly discussed.

hep-ph↗
arXiv2024

Extraction of the $S$-wave and $P$-wave $DD^*$ scattering phase shifts using twisted boundary conditions

We present results of a lattice study of the $S$-wave and $P$-wave $DD^*$ scattering phase shifts using Lüscher's method under the twisted boundary conditions to investigate the doubly charmed tetraquark $T_{cc}^+$ observed by the LHCb collaboration. Although the scattering phase shift at zero momentum gives information about the number of bound states according to Levinson's theorem, Lüscher's method under the periodic boundary condition only accesses the scattering phase shifts at some discrete momenta and is not suitable for watching the signal of bound state formation. On the other hand, the twisted boundary condition has the advantage that the scattering phase shift at any momentum can be calculated and that not only the $S$-wave scattering phase shift but also the $P$-wave scattering phase shift can be obtained simultaneously. In this study, we perform the simulation for the $DD^*$ and $BB^*$ systems in the $I=0$ channel using 2+1 flavor PACS-CS gauge ensembles simulated at $m_π=295$ and 411 $\mathrm{MeV}$.

hep-lat↗
arXiv2023

Prospects for the stout smearing as an equivalent approach to the Wilson flow

We present the equivalence between the Wilson flow and the stout smearing. The similarity between these two methods was first pointed out by Lüscher's original paper on the Wilson flow. We first show the analytical equivalence of two methods, which indicates that the finite stout smearing parameter induces ${\cal O}(a^2)$ correction. We secondly show that they remain equivalent in numerical simulations within some numerical precision even with finite cutoffs and stout smearing parameters by directly comparing the expectation values of the action density and we shortly mention the use of the equivalence.

hep-lat↗
arXiv2023

On the equivalence between the Wilson flow and stout-link smearing

We present the numerical equivalence between the Wilson flow and stout-link smearing, both of which are known to be a relatively new technique for smoothing the gauge fields on the lattice. Although the conceptional correspondence between two methods was first pointed out by Lüscher in his original paper [J. High Energy Phys.~08 (2010) 071], we provide a direct analytical proof of the equivalence between the two methods at finite lattice spacing $a$ in the zero limit of the stout-smearing parameter $ρ$. The leading order corrections start at ${\cal O}(ρ)$, which would induce ${\cal O}(a^2)$ corrections. It is, therefore, not obvious that they remain equivalent even with finite parameters ($a\neq 0$ and $ρ\neq0$) within some numerical precision. In this paper, we demonstrate the equivalence of both methods by directly comparing the expectation value of the action density, which is measured in actual numerical simulations.

hep-lat↗