arXiv subjects

Yasumichi Aoki

Publications and source records attributed to Yasumichi Aoki.

At least 19 recordsLinked to original sources

arXiv2026

A novel view of the flavor-singlet spectrum from multi-flavor QCD on the lattice

SU(3) gauge theories with increasing number of light fermions are the templates of strongly interacting sectors and studying their low-energy dynamics and spectrum is important, both for understanding the strong dynamics of QCD itself, but also for discovering viable UV completions of beyond the Standard Model physics. In order to contrast many-flavors strongly interacting theories with QCD on a quantitative footing, we use Lattice Field Theory simulations. We focus on the study of the flavor-singlet spectrum in the scalar and pseudoscalar channels: this is an interesting probe of the dynamics of the strongly interacting sector, as reminded by the QCD case with the $f_0(500)$ ($σ$) and $η^\prime$ mesons. The hierarchy of the spectrum of a strongly coupled new gauge sector of the Standard Model defines the potential reach of future colliders for new physics discoveries. In addition to a novel hierarchy with light scalars, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present a complete lattice study of both these flavor-singlet channels on high-statistics gauge ensembles generated by the LatKMI collaboration with 4, 8, and 12 copies of light mass-degenerate fermions. We also present other hadron masses on the lightest ensemble for $N_f=8$ generated by the LatKMI collaboration and discuss the chiral extrapolation of the spectrum in this particular theory. We contrast the results to $N_f=4$ simulations and previous results of $N_f=12$ simulations.

hep-lat↗

arXiv2026

The QCD phase diagram for three-flavor Möbius domain-wall fermions

We investigate the phase transition of Quantum Chromodynamics (QCD) with three degenerate quark flavors at zero baryon chemical potential. Using Möbius domain-wall fermions as the lattice fermion formulation, we ensure excellent chiral symmetry preservation. Our simulations are performed at three different temporal lattice extents, $N_{t}=6, 8, 12$, with a fixed lattice spacing $a=0.1361(20)$ fm, corresponding to temperatures of 242(4), 181(3), and 121(2) MeV, respectively. We explore a range of quark masses and spatial volumes with aspect ratios $N_{s}/N_{t}$ spanning from 2 to 4. By analyzing the mass and volume dependencies of the plaquette, plaquette susceptibility, chiral condensate, chiral susceptibilities, and Binder cumulant, we identify the pseudocritical transition quark masses from our largest lattice volumes. For $N_t=6$, this is 184(10) MeV (determined from the plaquette susceptibility). For $N_t=8$ and 12, the transition points vary slightly depending on whether the total or disconnected chiral susceptibility is used, yielding ranges of 36(1)-39.1(9) MeV and 3.5(3)-3.7(2) MeV, respectively, in the $\overline{\text{MS}}$ scheme at a scale of $μ=2$ GeV. The negligible volume dependence at $N_t=6$ and 8, combined with finite-size scaling analysis at $N_t=12$ revealing volume growth significantly weaker than expected for a first- or second-order phase transition, points to a continuous crossover at these specific quark mass points. Additionally, we study the effects of residual chiral symmetry breaking on the chiral condensate and chiral susceptibilities using two different values of $L_s$.

hep-lat↗

arXiv2026

Quark Number Susceptibilities and Conserved Charge Fluctuations in $(2+1)$-flavor QCD with Möbius domain-wall fermions (MDWF)

We calculate second- and selected fourth-order conserved-charge fluctuations in $(2+1)$-flavor QCD using Möbius domain-wall fermions (MDWF) along a line of constant physics. Gauge ensembles were generated for two light-to-strange quark-mass ratios, $m_l/m_s=1/10$ and $1/27.4$, corresponding to heavier-than-physical and physical pion masses, respectively. For $m_l/m_s=1/10$, calculations were carried out on lattices with temporal extents $N_τ=12$ and $16$, enabling an assessment of lattice-spacing effects at heavier pion mass. For $m_l/m_s=1/27.4$, calculations were performed at $N_τ=12$, allowing us to study the light-quark-mass dependence down to the physical point. Below the pseudocritical temperature, second-order electric-charge, strangeness, and off-diagonal conserved-charge fluctuations are consistent with QMHRG2020 hadron resonance gas calculations. Across the crossover region, these observables rise rapidly and tend toward their Stefan--Boltzmann limits. Selected fourth-order cumulants were also computed at the physical pion mass. Although these observables are statistically more demanding, several channels with controlled uncertainties permit a first comparison with hadron resonance gas calculations.

hep-lat↗

arXiv2026

Topological susceptibility and QCD phase transition with 2+1 flavor Möbius domain wall fermion at finite temperature

The topological susceptibility is one of the quantities that has a large discretization error, and the error can be sensitive to the choice of fermion action. We report on our results from physical point simulations with 2+1 flavor Möbius domain wall fermion at finite temperature. We also present the chiral condensate and disconnected susceptibility. The temporal lattice size is Nt=12 and 16, and the temperature range is around 140 MeV to 250 MeV for the chiral condensate and susceptibility. A coarse lattice with Nt = 10 covers up to 500 MeV to measure the topological susceptibility.

hep-lat↗

arXiv2026

Real radiative decays of heavy pseudoscalar mesons

We report our ongoing lattice QCD study of radiative leptonic decays of the charged pseudoscalar mesons $D$, $D_s$, $B$, and $B_c \to \ell ν_\ell γ$. We carry out our analysis on a single JLQCD ensemble with lattice spacing $a=0.044~\text{fm}$. This work is a step towards a complete QCD+QED lattice calculation of these modes, aimed at reducing theoretical uncertainties in the extraction of $|V_{cd}|$ and $|V_{cs}|$ and providing first-principles estimates of the corresponding form factors in the $B$ sector.

hep-lat↗

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

Method for high-precision determination of the nucleon axial structure using lattice QCD: Removing $πN$-state contamination

We performed a precise calculation of physical quantities related to the axial structure of the nucleon using 2+1 flavor lattice QCD gauge configuration (PACS10 configuration) generated at the physical point with lattice volume larger than $(10\;{\mathrm{fm}})^4$ by the PACS Collaboration. The nucleon matrix element of the axial-vector current has two types of the nucleon form factors, the axial-vector ($F_A$) form factor and the induced pseudoscalar ($F_P$) form factor. Recently lattice QCD simulations have succeeded in reproducing the experimental value of the axial-vector coupling, $g_A$, determined from $F_A(q^2)$ at zero momentum transfer $q^2=0$, at a percent level of statistical accuracy. However, the $F_P$ form factor so far has not reproduced the experimental values well due to strong $πN$ excited-state contamination. Therefore, we proposed a simple subtraction method for removing the so-called leading $πN$-state contribution, and succeeded in reproducing the values obtained by two experiments of muon capture on the proton and pion electro-production for $F_P(q^2)$. The novel approach can also be applied to the nucleon pseudoscalar matrix element to determine the pseudoscalar ($G_P$) form factor with the help of the axial Ward-Takahashi identity. The resulting form factors, $F_P(q^2)$ and $G_P(q^2)$, are in good agreement with the prediction of the pion-pole dominance model. In the new analysis, the induced pseudoscalar coupling $g_P^\ast$ and the pion-nucleon coupling $g_{πNN}$ can be evaluated with a few percent accuracy including systematic uncertainties using existing data calculated at two lattice spacings.

hep-lat↗

arXiv2025

Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics

Processes that violate baryon number, most notably proton decay and $n\bar n$ transitions, are promising probes of physics beyond the Standard Model (BSM) needed to understand the lack of antimatter in the Universe. To interpret current and forthcoming experimental limits, theory input from nuclear matrix elements to UV complete models enters. Thus, an interplay of experiment, effective field theory, lattice QCD, and BSM model building is required to develop strategies to accurately extract information from current and future data and maximize the impact and sensitivity of next-generation experiments. Here, we briefly summarize the main results and discussions from the workshop "INT-25-91W: Baryon Number Violation: From Nuclear Matrix Elements to BSM Physics," held at the Institute for Nuclear Theory, University of Washington, Seattle, WA, January 13-17, 2025.

hep-ph↗

arXiv2025

Symmetry of screening masses of mesons in two-flavor lattice QCD at high temperatures

We investigate spatial two-point correlation functions of mesonic operators in two-flavor lattice QCD at high temperatures. The simulated temperatures over the range $T \in [147, 330]$ MeV, where the critical temperature is estimated around 165 MeV. To ensure a good control of the chiral symmetry we employ the Möbius domain-wall fermion action for two degenerate flavors of quarks. With a lattice cut off $a^{-1}\sim 2.6$ GeV, the residual mass is reduced to 0.14 MeV. With the energy spectrum obtained from the screening mass at incremental values of the temperature range, we examine the $SU(2)_L\times SU(2)_R$ chiral symmetry, the anomalous axial $U(1)$ as well as an enhanced symmetry which exchanges the spin degrees of freedom. We also study how the data approaches the perturbative prediction given by twice the Matsubara frequency of free quarks.

hep-lat↗

arXiv2025

Investigating the axial structure of the nucleon based on large-volume lattice QCD at the physical point

We present a short summary for the calculations of the nucleon $\textit{isovector}$ form factors, which are relevant to improving the accuracy of the current neutrino oscillation experiments. The calculations are carried out with two of three sets of the $2+1$ flavor lattice QCD configurations generated at the physical point in large spatial volumes by the PACS Collaboration. The two gauge configurations are generated with the six stout-smeared $O(a)$ improved Wilson quark action and Iwasaki gauge action at the lattice spacing of $0.09$ fm and $0.06$ fm. We summarize the results for three form factors as well as the nucleon axial-vector ($g_A$), induced pseudoscalar ($g_P^*$) and pion-nucleon ($g_{πNN}$) couplings. Although our couplings agree with the experimental data, a firm conclusion should be drawn only after a continuum limit extrapolation is taken. We investigate the partially conserved axial-vector current (PCAC) relation in the context of the nucleon correlation functions. The low-energy relations arising from the PCAC relation can be used to verify whether the lattice QCD data correctly reproduce the physics in the continuum within the statistical accuracy. It is demonstrated that our $\textit{new analysis}$ reduces the systematic uncertainty for the induced pseudoscalar and pseudoscalar form factors to a greater extent than the $\textit{traditional analysis}$, and the results offer a theoretical insight into the pion-pole dominance model. Finally, we examine the applicable $q^2$ region for the low-energy relations.

hep-lat↗

arXiv2025

A proposal for removing $πN$-state contamination from the nucleon induced pseudoscalar form factor in lattice QCD

In the PACS10 project, the PACS collaboration has generated three sets of the PACS10 gauge configurations at the physical point with lattice volume larger than $(10\;{\rm fm})^4$ and three different lattice spacings. The isovector nucleon form factors had been already calculated by using two sets of the PACS10 gauge configurations. In our strategy, the smearing parameters of the nucleon interpolation operator were highly optimized to eliminate as much as possible the contribution of excited states in the nucleon two-point function. This strategy was quite successful in calculations of the electric ($G_E$), magnetic ($G_M$) and axial-vector ($F_A$) form factors, while the induced pseudoscalar ($F_P$) and pseudoscalar ($G_P$) form factors remained strongly affected by residual contamination of $πN$-state contribution. In this work, we propose a simple method to remove the $πN$-state contamination from the $F_P$ form factor, and then evaluate the induced pseudoscalar charge $g_P^\ast$ and the pion-nucleon coupling $g_{πNN}$ from existing data in a new analysis. Applying this method to the $G_P$ form factor is also considered with a help of the axial Ward-Takahashi identity.

hep-lat↗

arXiv2025

Lattice gauge ensembles and data management

We summarize the status of lattice QCD ensemble generation efforts and their data management characteristics. Namely, these proceedings combine the contributions to a dedicated parallel session during the 41st International Symposium on Lattice Field Theory (Lattice 2024), during which representatives of 16 lattice QCD collaborations provided details on their simulation program, with focus on plans for publication, data management, and storage requirements. The parallel session was organized by the International Lattice Data Grid (ILDG), following an open call to the lattice QCD community for participation in the session.

hep-lat↗

arXiv2025

Three flavor QCD phase transition with Möbius domain wall fermions

We present an updated study of the $N_f=3$ QCD phase transition using Möbius domain wall fermions. Simulations were performed on $N_t=12$ lattices with aspect ratios ranging from 2 to 4 for various quark masses, at a lattice spacing of $a=0.1361(20)$ fm, corresponding to a temperature of 121(2) MeV. To clarify the nature of the phase transition, a large-volume lattice, $48^3 \times 12\times 16$, was added to analyze the volume dependence of disconnected chiral susceptibility. By examining the chiral condensate, disconnected chiral susceptibility, and Binder cumulant, and incorporating results from $24^3 \times 12 \times 16$ and $36^3 \times 12 \times 16$ lattices reported in earlier studies, we observe that the transition is consistent with a crossover at a quark mass of approximately $m_f^{\mathrm{\overline {MS}}}(2\, \mathrm{GeV}) \sim 4$ MeV at this temperature. Furthermore, we discuss the effects of residual chiral symmetry breaking on the chiral condensate and disconnected chiral susceptibility for different sizes in the 5th direction.

hep-lat↗

arXiv2025

Study of symmetries in finite temperature $N_f=2$ QCD with Möbius Domain Wall Fermions

We report on the ongoing study of symmetry of $N_f=2$ QCD around the critical temperature. Our simulations of $N_f = 2$ QCD employ the Möbius domain-wall fermion action with residual mass $\sim 1\mbox{MeV}$ or less, maintaining a good chiral symmetry. Using the screening masses from the two point spatial correlators we compare the mass difference between channels connected through various symmetry transformations. Our analysis focuses on restoration of the $SU(2)_L\times SU(2)_R$ as well as anomalously broken axial $U(1)_A$. We also present additional study of a potential $SU(2)_{CS}$ symmetry which may emerge at sufficiently high temperatures.

hep-lat↗

arXiv2025

Studies of nucleon isovector structure with the PACS10 superfine lattice

We present the results for the nucleon axial-vector, induced pseudoscalar and pion-nucleon couplings obtained from 2+1 flavor lattice QCD at the physical point with a large spatial extent of about 10 fm. Our calculations are performed with the PACS10 gauge configurations generated by the PACS Collaboration with the six stout-smeared $O(a)$ improved Wilson-clover quark action and Iwasaki gauge action at $β$ = 1.82, 2.00 and 2.20 corresponding to lattice spacings of 0.09 fm (coarse), 0.06 fm (fine) and 0.04 fm (superfine), respectively. We first evaluate the value of the nucleon axial-vector coupling. In addition, the induced pseudoscalar and pion-nucleon couplings from the induced pseudoscalar form factor are also investigated. Combining the results obtained from the all of our coarse, fine and superfine lattices, we finally discuss the systematic uncertainties in our calculation based on the comparison with both of the experimental values and lattice QCD results provided by the other collaborations.

hep-lat↗

arXiv2025

Proton decay matrix elements on PACS configurations

We report the preliminary results of lattice computation for the proton decay matrix elements in $N_f=2+1$ physical point with Wilson-clover fermion. We perform it on the PACS configurations of $64^4$ lattice volume with lattice spacing $a=0.085$ fm, and carefully estimate the systematic uncertainties, especially for the excited state contamination and associated error of the renormalization constant with Regularization Independent (RI, Rome-Southampton) scheme. Our preliminary results of the twelve relevant transition modes in proton decay matrix element and comparison with other lattice results are presented.

hep-lat↗

arXiv2025

Quark number susceptibility and conserved charge fluctuation for (2+1)-flavor QCD with Möbius domain wall fermions

We present quark number susceptibilities and conserved charge fluctuations for (2+1)-flavor QCD using Möbius Domain Wall fermions with a pion mass of $135~\rm{MeV}$. Our results are compared with hadron resonance gas models below the QCD transition temperature and with $\mathcal{O}(g^2)$ perturbation theory at high temperatures. Additionally, we compare our findings with results from staggered fermion discretizations. Furthermore, we also present results of leading order Kurtosis of electric charge and strangeness fluctuations.

hep-lat↗

arXiv2024

Nucleon form factors in $N_f=2+1$ lattice QCD at the physical point : finite lattice spacing effect on the root-mean-square radii

We present results for the nucleon form factors: electric ($G_E$), magnetic ($G_M$), axial ($F_A$), induced pseudoscalar ($F_P$) and pseudoscalar ($G_P$) form factors, using the second PACS10 ensemble that is one of three sets of $2+1$ flavor lattice QCD configurations at physical quark masses in large spatial volumes (exceeding $(10\ \mathrm{fm})^3$). The second PACS10 gauge configurations are generated by the PACS Collaboration with the six stout-smeared $O(a)$ improved Wilson quark action and Iwasaki gauge action at the second gauge coupling $β=2.00$ corresponding to the lattice spacing of $a=0.063$ fm. We determine the isovector electric, magnetic and axial radii and magnetic moment from the corresponding form factors, as well as the axial-vector coupling $g_A$. Combining our previous results for the coarser lattice spacing [E. Shintani et al., Phys. Rev. D99 (2019) 014510; Phys. Rev. D102 (2020) 019902 (erattum)], the finite lattice spacing effects on the isovector radii, magnetic moment and axial-vector coupling are investigated using the difference between the two results. It was found that the effect on $g_A$ is kept smaller than the statistical error of 2% while the effect on the isovector radii was observed as a possible discretization error of about 10%, regardless of the channel. We also report the partially conserved axial vector current (PCAC) relation using a set of nucleon three-point correlation functions in order to verify the effect by $O(a)$-improvement of the axial-vector current.

hep-lat↗