arXiv subjects

Hideo Matsufuru

Publications and source records attributed to Hideo Matsufuru.

At least 19 recordsLinked to original sources

arXiv2026

Bifurcated Impact of Neutrino Fast Flavor Conversion on Core-collapse Supernovae Informed by Multi-angle Neutrino Radiation Hydrodynamics

In this {\it Letter}, we present a compelling and robust argument for the roles of neutrino fast flavor conversion (FFC) in the explosion mechanism of core-collapse supernova (CCSN), combining the {\it multi-angle} FFC subgrid model rooted in quantum kinetic theory with the multi-dimensional four-species Boltzmann neutrino radiation hydrodynamics. Employing various progenitor masses and the nuclear equations of states, we find that the effect of FFC on CCSN explosion is bifurcated depending on the progenitors. For the lowest-mass progenitor, FFC facilitates the shock revival and enhances the explosion energy, whereas for higher-mass progenitors its impact is inhibitory. We identify the mass accretion rate as the key determinant governing this bifurcation. When the mass accretion rate is low (high), the contribution of FFC to neutrino heating becomes positive (negative), because the heating efficiency enhancement via FFC-driven spectral hardening of electron-type neutrinos dominates over (is outweighed by) the concurrent reduction in neutrino luminosity. Our results further highlight the limitations of approximate neutrino transport, and demonstrate that a multi-angle treatment is essential for accurately capturing FFC effects; otherwise, FFCs are missed and even generated spuriously.

astro-ph.HE↗

arXiv2026

Accelerating iterative linear equation solver using modified domain-wall fermion matrix in lattice QCD simulations

Lattice simulations of Quantum Chromodynamics (QCD) enable one to calculate the low-energy properties of the strong interaction among quarks and gluons based on the first principle. The most time-consuming part of the numerical simulations of lattice QCD is typically solving a linear equation for the quark matrix. In particular, a discretized quark formulation called the domain-wall fermion operator requires a high numerical cost, while retaining the lattice version of the chiral symmetry to good precision. The domain-wall operator is defined on a five-dimensional (5D) space extending the four-dimensional (4D) spacetime with an extra fifth coordinate. After solving the linear equation in 5D space, the result vector is projected onto the original 4D space. There is a variant of the domain-wall operator that improves the convergence of the 5D linear equation while unchanging the 4D solution vector. In this paper, we examine how this variant of the domain-wall operator accelerates the iterative linear equation solver in practical setups. We also measure the eigenvalues of the operator and compare the condition number with the convergence of the solver. We use a generic lattice QCD code set Bridge++ that is planned to be released including the improved form of the domain-wall operator examined in this work with code for the GPU.

hep-lat↗

arXiv2026

Mixed precision solvers with half-precision floating point numbers for Lattice QCD on A64FX processor

We investigate the use of half-precision floating-point numbers (FP16) in mixed-precision linear solvers for lattice QCD simulations. Since the emergence of GPUs for general-purpose, mixed-precision algorithms that combine single-precision (FP32) with double-precision (FP64) arithmetics have become widely used in this field and others. While FP32-based methods are now well established, we examine the practicality of using FP16. In this work, we introduce rescaling steps in both the outer iterative refinement step and the inner BiCGStab solver to avoid numerical instability. In our experiments with a simple Wilson kernel, the solver shows improved stability, and the additional iteration count compared to the FP64 version remains within 20\%, indicating that the FP16 version is practical for use. We believe that the proposed rescaling methods can also benefit other mixed precision preconditioners in avoiding underflows.

hep-lat↗

arXiv2025

On the validity of the complex Langevin method near the deconfining phase transition in QCD at finite density

In our previous paper [JHEP 10 (2020) 144], we found that the complex Langevin (CL) method works for QCD at finite density on the $16^3 \times 32$ lattice in the low-temperature high-density regime within the range $μ/ T = 1.6 - 9.6$ with $μ$ and $T$ being the quark chemical potential and the temperature, which enabled us to see a clear trend towards the formation of the Fermi sphere. Here we investigate the validity of the CL method on the $24^3 \times 12$ lattice in the deconfined phase near the deconfinement phase transition. As before, we use four-flavor staggered fermions and judge the validity using the criterion based on the probability distribution of the drift term. The spatial extent is $L = (1.3 - 2.7 {\rm ~fm} )> Λ_{\rm LQCD}^{-1} \sim 1{\rm ~fm}$, in contrast to our previous study with $L < Λ_{\rm LQCD}^{-1}$. We find that the CL method works in a broad region up to $μ/ T = 4.8$, while it starts to fail as we approach the phase boundary due to the singular drift problem, which can be understood qualitatively by extending the Banks-Casher relation to the case at finite density.

hep-lat↗

arXiv2025

International Lattice Data Grid 2.0: Status and Progress

In this proceeding contribution we discuss the status and progress towards a modernised and extended International Lattice Data Grid (ILDG), which has seen major developments, updates, and upgrades over the last year. In particular, metadata and file schemata have been extended. Moreover, the registration and authentication services have been modernised, and the file and metadata catalogues re-implemented.

hep-lat↗

arXiv2023

Wilson matrix kernel for lattice QCD on A64FX architecture

We study the implementation of the even-odd Wilson fermion matrix for lattice QCD simulations on the A64FX architecture. Efficient coding of the stencil operation is investigated for two-dimensional packing to SIMD vectors. We measure the sustained performance on the supercomputer Fugaku at RIKEN R-CCS and show the profiler result of our code, which may signal an unexpected source of slow-down in addition to the detailed efficiency of each part of the code.

cs.DC↗

arXiv2023

Bridge++ 2.0: Benchmark results on supercomputer Fugaku

Bridge++ is a general-purpose code set for lattice QCD simulations aiming at a readable, extensible, and portable code while keeping practical high performance. The new version 2.0 employs machine-dependent optimization, enabling flexible data layout in float/double precision, while it was fixed layout and only with the double precision in previous versions. We report the performance on supercomputer Fugaku with Arm A64FX-SVE architecture by Fujitsu.

hep-lat↗

arXiv2023

Color superconductivity on the lattice -- analytic predictions from QCD in a small box

We investigate color superconductivity on the lattice using the gap equation for the Cooper pair condensate. The weak coupling analysis is justified by choosing the physical size of the lattice to be smaller than the QCD scale, while keeping the aspect ratio of the lattice small enough to suppress thermal excitations. In the vicinity of the critical coupling constant that separates the superconducting phase and the normal phase, the gap equation can be linearized, and by solving the corresponding eigenvalue problem, we obtain the critical point and the Cooper pair condensate without assuming its explicit form. The momentum components of the condensate suggest spatially isotropic s-wave superconductivity with Cooper pairs formed by quarks near the Fermi surface. The chiral symmetry in the massless limit is spontaneously broken by the Cooper pair condensate, which turns out to be dominated by the scalar and the pseudo-scalar components. Our results provide useful predictions, in particular, for future lattice simulations based on methods to overcome the sign problem such as the complex Langevin method.

hep-lat↗

arXiv2022

Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation-Hydrodynamics Code

We investigate the protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation-hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a snapshot of a PNS at 2.3 seconds after bounce from a 1D PNS cooling calculation and run our simulation for $\sim160\,\mathrm{ms}$ in 2D under axisymmetry. The original PNS cooling calculation neglected convection entirely and the initial condition is linearly unstable to convection. We find in our 2D simulation that convection is instigated there indeed and expands inward after being full-fledged. The convection is then settled to a quasi-steady state in $\sim100\,\mathrm{ms}$, being sustained by the negative $Y_e$ gradient, which is in turn maintained by neutrino emissions. It enhances the luminosities and mean energies of all species of neutrinos compared to 1D. Taking advantage of the Boltzmann solver, we analyze the possible occurrence of the neutrino fast flavor conversion (FFC). We found that FFC is likely to occur in the regions, where $Y_e$ is lower, and that the growth rate can be as high as $\sim 10^{-1}\,{\mathrm{cm}^{-1}}$.

astro-ph.HE↗

arXiv2022

Principal-Axis Analysis of the Eddington Tensor for the Early Post-Bounce Phase of Rotational Core-Collapse Supernovae

Using full Boltzmann neutrino transport, we performed two-dimensional (2D) core-collapse supernova simulations in axisymmetry for two progenitor models with 11.2M and 15.0M both rotational and non-rotational. We employed the results obtained in the early post-bounce phase (t < 20 ms) to assess performance under rapid rotation of some closure relations commonly employed in the truncated moment method. We first made a comparison in 1D under spherical symmetry, though, of the Eddington factor p defined in the fluid rest frame (FR). We confirmed that the maximum entropy closure for the Fermionic distribution (MEFD) performs better than others near the proto-neutron star surface, where p < 1/3 occurs, but does not work well even in 1D when the phase space occupancy satisfies e < 0.5 together with p < 1/3, the condition known to be not represented by MEFD. For the 2D models with the rapid rotation, we employed the principal-axis analysis of the Eddington tensor. We paid particular attention to the direction of the longest principal axis. We observed in FR that it is aligned neither with the radial direction nor with the neutrino flux in 2D, particularly so in convective and/or rapidly rotating regions, the fact not accommodated in the moment method. We repeated the same analysis in the laboratory frame (LB) and found again that the direction of the longest principal axis is not well reproduced by MEFD because the interpolation between the optically thick and thin limits is not very accurate in this frame.

astro-ph.HE↗

arXiv2021

Multigrid Solver on Fugaku

We report an implementation of a multigrid solver for the Clover fermion on supercomputer Fugaku, which uses A64FX CPU with Arm architecture. On Fugaku, a highly optimized implementation of BiCGStab solver with domain decomposed preconditioner for the Clover fermion, called QCD Wide SIMD library (QWS), is available. We use the preconditioner in QWS as a smoother of the multigrid solver. Our implementation shows reasonably good scaling and performance. The code is developed by using Bridge++ code framework and its extension.

hep-lat↗

arXiv2021

Color superconductivity in a small box: a complex Langevin study

It is expected that the color superconductivity (CSC) phase appears in QCD at low temperature and high density. On the basis of the lattice perturbation theory, a possible parameter region in which the CSC occurs has been predicted. In this work, we perform complex Langevin simulation on an $8^3\times 128$ lattice using four-flavor staggered fermions. We find, in particular, that the quark number has plateaux with respect to the chemical potential similar to our previous study, indicating the formation of the Fermi sphere. A diquark-antidiquark operator, which is an order parameter of color superconductivity, is formulated on the lattice using the U(1) noise. Our result for this operator is found to fluctuate violently when the Fermi surface coincides with the energy levels of quarks. We also discuss partial restoration of the chiral symmetry at high density.

hep-lat↗

arXiv2021

Flavor number dependence of QCD at finite density by the complex Langevin method

We discuss the flavor number dependence of QCD at low temperature and high density by the complex Langevin method. In our previous work, the complex Langevin method is confirmed to satisfy the criterion for correct convergence in certain regions, such as $μ_{\rm q} / T = 5.2-7.2$ on $8^3 \times 16$ and $μ_{\rm q} / T = 1.6-9.6$ on $16^3 \times 32$ using $N_{\rm f} = 4$ staggered fermion at $β= 5.7$. We extend this study to more realistic flavor cases, $N_{\rm f} = 2, 2 + 1, 3$, using Wilson fermions. We present the flavor number dependence of the validity regions of the complex Langevin method and the quark number.

hep-lat↗

arXiv2021

Perturbative predictions for color superconductivity on the lattice

We develop a new method to investigate color superconductivity (CSC) on the lattice based on the Thouless criterion, which amounts to solving the linearized gap equation without imposing any ansatz on the structure of the Cooper pairs. We perform explicit calculations at the one-loop level with the staggered fermions on a $8^3 \times 128$ lattice and the Wilson fermions on a $4^3 \times 128$ lattice, which enables us to obtain the critical $β(=6/g^2)$ as a function of the quark chemical potential $μ$, below which the CSC phase is expected to appear. The obtained critical $β$ has sharp peaks at the values of $μ$ corresponding to the discretized energy levels of quarks similarly to what was observed in previous studies on simplified effective models. From the solution to the linearized gap equation, one can read off the flavor and spatial structures of the Cooper pairs at the critical $β$. In the case of massless staggered fermion, in particular, we find that the chiral $\mathrm{U}(1)$ symmetry of the staggered fermions is spontaneously broken by the condensation of the Cooper pairs.

hep-lat↗

arXiv2021

Object-oriented implementation of algebraic multi-grid solver for lattice QCD on SIMD architectures and GPU clusters

A portable implementation of elaborated algorithm is important to use variety of architectures in HPC applications. In this work we implement and benchmark an algebraic multi-grid solver for Lattice QCD on three different architectures, Intel Xeon Phi, Fujitsu A64FX, and NVIDIA Tesla V100, in keeping high performance and portability of the code based on the object-oriented paradigm. Some parts of code are specific to an architecture employing appropriate data layout and tuned matrix-vector multiplication kernels, while the implementation of abstract solver algorithm is common to all architectures. Although the performance of the solver depends on tuning of the architecture-dependent part, we observe reasonable scaling behavior and better performance than the mixed precision BiCGSstab solvers.

hep-lat↗

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.

hep-lat↗

arXiv2021

102 PFLOPS Lattice QCD quark solver on Fugaku

We present results on the world's first over 100 PFLOPS single precision lattice QCD quark solver on the japanese new supercomputer Fugaku. We achieve a factor 38 time speedup from the supercomputer K on the same problem size, $192^4$, with 102 PFLOPS, 10% floating-point operation efficiency against single precision floating-point operation peak. The evaluation region is the single precision BiCGStab for a Clover-Wilson Dirac matrix with Schwarz Alternating Procedure domain decomposition preconditioning using Jacobi iteration for the local domain matrix inversion.

hep-lat↗

arXiv2021

Gravitational Wave Physics and Astronomy in the nascent era

The detections of gravitational waves (GW) by LIGO/Virgo collaborations provide various possibilities to physics and astronomy. We are quite sure that GW observations will develop a lot both in precision and in number owing to the continuous works for the improvement of detectors, including the expectation to the newly joined detector, KAGRA, and the planned detector, LIGO-India. In this occasion, we review the fundamental outcomes and prospects of gravitational wave physics and astronomy. We survey the development focusing on representative sources of gravitational waves: binary black holes, binary neutron stars, and supernovae. We also summarize the role of gravitational wave observations as a probe of new physics.

gr-qc↗