arXiv subjects

Sinya Aoki

Publications and source records attributed to Sinya Aoki.

At least 19 recordsLinked to original sources

arXiv2026

An analytic model for a total process of gravitational collapse: From star to Schwarzschild black hole

We present an exact analytical model describing a complete gravitational collapse of matter from horizonless initial conditions to black hole formation, tracing the full evolution of the horizon $H(t)$ from its formation at microscopic scales to macroscopic stabilization. The solution reveals two main stages: (i) a dynamical horizon growth, where an apparent horizon $H(t)$ emerges at a critical time $t_b$ until reaching its final size $h=2 M$, demonstrating how trapped surfaces form dynamically in finite time, and (ii) a {naked-}singularity resolution, where an integrable Ricci curvature singularity ($R^\mu{}_\nu \sim r^{-2}$) develops at $r=0$, but remains causally hidden by the horizon growth, preserving weak cosmic censorship without exotic matter. The model could offer a framework to study the quantum-to-classical transition ($H(t) \sim \ell_{\rm Planck}$).

gr-qc↗

arXiv2026

Reply to "Comment on "Chiral symmetry restoration, the eigenvalue density of the Dirac operator, and the axial U(1) anomaly at finite temperature""

We respond to the comment by Matteo Giordano [1] on our article [2]. We find -- and [1] itself acknowledges -- that the proposed counterexamples intended to refute our argument violate a crucial assumption of QCD at high temperatures, namely that every gluonic observable is an analytic function of the squared quark mass, $m^2$. We further point out a technical mistake found in [1]. We conclude that the arguments presented in [1] are not valid.

hep-lat↗

arXiv2025

Is energy conserved in general relativity ?

This short report is dedicated to the 40th anniversary of International Journal of Modern Physics A (IJMPA) and Modern Physics Letters A (MPLA). While the report is based on a series of papers[1-8], its content reflects my personal viewpoints. Therefore I am solely responsible for all the statements in the report. In this report we discuss conservation of energies in a curved spacetime including general relativity. We argue that the matter energy is not necessarily conserved in a curved space time due to a lack of time translational invariance, and adding energy of gravitational fields to recover the conservation law of energies fails due to Noether's 2nd theorem. We show that there exists conserved quantities associated with the matter energy momentum tensor other than the energy in a curved spacetime, and discuss consequences of the existence of such conserved charges.

gr-qc↗

arXiv2025

$S$-wave kaon-nucleon interactions from lattice QCD at the physical point

We investigate S-wave kaon-nucleon ($KN$) interactions with strangeness $S=+1$ in lattice QCD using the time-dependent HAL QCD method. Employing the $(2+1)$-flavor gauge configuration with $m_{\pi}\approx 137~\textrm{MeV}$ and $m_{K}\approx 502~\textrm{MeV}$, we calculate the $KN$ potentials at the leading order in the derivative expansion. The potentials in both isospin channels ($I=1$ and $I=0$) exhibit repulsion at short distances, while only the $I=0$ potential has a small attractive pocket at intermediate distances. From these potentials, we compute the phase shifts as well as the low-energy scattering parameters. The obtained phase shifts show no signals corresponding to resonances or bound states in both isospin channels, suggesting the absence of the $\Theta^{+}(1540)$ pentaquark in the S-wave $KN$ systems. The results for $I=0$ suggest that the scattering amplitudes in this channel are dominated by P-wave components rather than S-wave.

hep-lat↗

arXiv2025

Decoding Two-Particle States in QCD with Spatial Wavefunctions

A systematic framework for constructing optimized interpolating operators strongly coupled to QCD two-particle states is developed, which is achieved by incorporating inter-hadron spatial wavefunctions. To efficiently implement these operators in lattice QCD, a novel quark smearing technique utilizing noise vectors is proposed. Applied to the $\Omega_{ccc}\Omega_{ccc}$ system, these optimized operators prove superior to combinations of limited plane-wave operators, enabling the resolution of distinct eigenstates separated by only $\sim 5$ MeV near the threshold $2m_{\Omega_{ccc}} \simeq 9700$ MeV. This exceptional resolving power opens new possibilities for studies of a wide range of hadronic systems in QCD.

hep-lat↗

arXiv2025

Wavefunction-based operator optimization for two-hadron systems in lattice QCD

A systematic way to constructing optimized interpolating operators for two-hadron systems is developed by incorporating inter-hadron spatial wavefunctions. The wavefunctions can be obtained from an iterative process with an appropriate initial guess. To implement these operators, a novel quark smearing technique utilizing $Z_3$ noise vectors is proposed, which allows for effectively incorporating inter-hadron spatial wavefunctions at the source without using all-to-all quark propagators. Proof-of-principle application to the $\Omega_{ccc}\Omega_{ccc}$ system using physical-point lattice configurations with a large size $La\simeq8.1$~fm demonstrates that optimized operators outperform combinations of limited plane-wave operators in the variational analysis, enabling clear identification of states around $2m_{\Omega_{ccc}}\simeq 9700$ MeV with the energy gap as narrow as $\sim 5$ MeV. A comparison on correlation functions, effective energies, and HAL QCD potentials between unoptimized operators and optimized operators is given, with a special emphasis on the effects from nearby elastic scattering states. Potential applicability of the optimized operator to various two-hadron systems and its relation to the variational method are also discussed.

hep-lat↗

arXiv2025

Interaction between two hadrons in lattice QCD

I report recent developments on hadron interactions in lattice QCD by the HAL QCD method. As an introduction, I summarize the lattice community's consensus on the absence of the deeply bound dinucleons at heavier pion masses. We then present 4 results by the HAL QCD method using $2+1$ flavor QCD gauge configurations at $m_\pi \simeq 146$ MeV and $a\simeq 0.0846$ fm, which are the $\Lambda\Lambda-N\Xi$ interactions, $N\Omega$ dibaryon, the tetra-quark state $T_{cc}$ and the $N-\phi$ interaction with the 2-pion tail. A brief summary follows.

hep-lat↗

arXiv2025

$\Lambda$(1405) in the flavor SU(3) limit using a separable potential in the HAL QCD method

Using the HAL QCD method, we investigate S-wave meson-baryon interactions in singlet and two octet channels in the flavor SU(3) limit, where the chiral unitary model predicts that a combination of bound-state poles in these channels corresponds to $\Lambda(1405)$. To avoid the singular behavior of the leading-order potentials of these channels in the derivative expansion, we instead employ a separable potential in the time-dependent HAL QCD method. To calculate all-to-all propagators in the three-point correlation functions including $\Lambda$-baryon source operators with zero momentum, we employ the conventional stochastic estimation combined with the covariant approximation averaging. Separable potentials both in the singlet and octet channels show attraction without singular behavior. Our results of the corresponding phase shifts indicate that the attractive interaction in the singlet channel is stronger than that in the octet. Binding energies are consistent with the estimates from the two-point correlation function within one (two) sigma for the singlet (octet) channel, and this ordering of binding energies is consistent with the mass hierarchy suggested by the chiral unitary model.

hep-lat↗

arXiv2025

Left-hand cut and the HAL QCD method

We investigate how the left-hand cut (LHC) problem is treated in the HAL QCD method. For this purpose, we first consider the effect of the LHC to the scattering problem in non-relativistic quantum mechanics with potentials. We show that the $S$-matrix or the scattering phase shift obtained from the potential including the Yukawa term ($e^{- m_\pi r}/r$) with the infra-red (IR) cutoff $R$ is well-defined even for the complex momentum $k$ as long as $R$ is finite, and they are compared with those obtained by the analytic continuation without the IR cutoff. In the $R\to\infty$ limit, the phase shift approaches the result from the analytic continuation at ${\rm Im}\, k < m_\pi/2$, while they differ at ${\rm Im}\, k > m_\pi/2$, except $k= k_b$, where $k_b$ is the binding momentum. We also observe that $k_b$ can be correctly obtained even at finite but large $R$. Using knowledge obtained in the non-relativistic quantum mechanics, we present how we should treat the LHC in the HAL QCD potential method.

hep-lat↗

arXiv2024

Study of symmetries in finite temperature $N_f=2$ QCD with M\"obius 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 M\"obius 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↗

arXiv2024

Derivation of the GKP-Witten relation by symmetry without Lagrangian

We derive the GKP-Witten relation in terms of correlation functions by symmetry without referring to a Lagrangian or the large $N$ expansion. By constructing bulk operators from boundary operators in conformal field theory (CFT) by the conformal smearing, we first determine bulk-boundary 2-pt functions for an arbitrary spin using both conformal and bulk symmetries, then evaluate their small $z$ behaviors, where $z$ is the $(d+1)$-th coordinate in the bulk. Next, we explicitly determine small $z$ behaviors of bulk-boundary-boundary 3-pt functions also by the symmetries, while small $z$ behaviors of correlation functions among one bulk and $n$ boundary operators with $n\ge 3$ are fixed by the operator product expansion (OPE). Combining all results, we construct the GKP-Witten relation in terms of these correlation functions at all orders in an external source $J$. We compare our non-Lagrangian approach with the standard approach employing the bulk action. Our results indicate that the GKP-Witten relation holds not only for holographic CFTs but also for generic CFTs as long as certain conditions are satisfied.

hep-th↗

arXiv2024

Analytic models for gravitational collapse

We present two analytical models of gravitational collapse toward the Schwarzschild black hole, starting from the interior of the revisited Schwarzschild solution recently reported in [Phys. Rev. D 109, 104032 (2024)]. Both models satisfy some energy conditions at all times as long as the collapse is slower than some limit. While a singularity of the Schwarzschild black hole at the origin ($R_{\mu\nu\alpha\beta}R^{\mu\nu\alpha\beta}\sim r^{-6}$) forms immediately after the start of the collapse in one model, such a singularity never appear at finite time during the collapse (except $t\to\infty$) in the other model. The scheme used shows great potential for studying in detail the appearance of singularities in general relativity.

gr-qc↗

arXiv2024

AdS/CFT correspondence for the $O(N)$ invariant critical $\varphi^4$ model in 3-dimensions by the conformal smearing

We investigate a structure of a 4-dimensional bulk space constructed from the $O(N)$ invariant critical $\varphi^4$ model in 3-dimension using the conformal smearing. We calculate a bulk metric corresponding to the information metric and the bulk-to-boundary propagator for a composite scalar field $\varphi^2$ in the large $N$ expansion. We show that the bulk metric describes an asymptotic AdS space at both UV (near boundary) and IR (deep in the bulk) limits, which correspond to the asymptotic free UV fixed point and the Wilson-Fisher IR fixed point of the 3-dimensional $\varphi^4$ model, respectively. The bulk-to-boundary scalar propagator, on the other hand, encodes $\Delta_{\varphi^2}$ (the conformal dimension of $\varphi^2$) into its $z$ (a coordinate in the extra direction of the AdS space) dependence. Namely it correctly reproduces not only $\Delta_{\varphi^2}=1$ at UV fixed point but also $\Delta_{\varphi^2}=2$ at the IR fixed point for the boundary theory. Moreover, we confirm consistency with the GKP-Witten relation in the interacting theory that the coefficient of the $z^{\Delta_{\varphi^2}}$ term in $z\to 0$ limit agrees exactly with the two-point function of $\varphi^2$ including an effect of the $\varphi^4$ interaction. }

hep-th↗

arXiv2024

Lattice QCD and Baryon-Baryon Interactions

In this chapter, the current status on baryon-baryon interactions such as nuclear forces in lattice Quantum ChromoDynamics (QCD) is reviewed. In studies of baryon-baryon interactions in lattice QCD, the most reliable method so far is the potential method, proposed by the Hadrons to Atomic nuclei from Lattice QCD (HAL QCD) collaboration, whose formulation, properties and extensions are explained in detail. Using the HAL QCD potential method, potentials between nucleons (proton and neutron, denoted by $N$) in the derivative expansion have been extracted in various cases. The lattice QCD results shown in this chapter include a Leading Order (LO) central potential in the parity-even $NN(^1S_0)$ channel, LO central and tensor potentials in the parity-even $NN(^3S_1$-$^3D_1)$ channel, and a Next-to-Leading Order (NLO) spin-orbit potential as well as LO potentials in the parity-odd channels. Preliminary results at the almost physical pion and kaon masses, in addition to exploratory studies on three-nucleon potentials, are presented. Interactions between generic baryons including hyperons, made of one or more strange quarks as well as up and down quarks, have also been investigated. Universal properties of potentials between baryons become manifest in the flavor SU(3) symmetric limit, where masses of three quarks, up, down and strange, are all equal. In particular, it is observed that one bound state, traditionally called the $H$-dibaryon, appears in the flavor singlet representation of SU(3). A fate of the $H$ dibaryon is also discussed with flavor SU(3) breaking taken into account at the almost physical point. Finally, various kinds of dibaryons, bound or resonate states of two baryons, including charmed dibaryons, have been predicted by lattice QCD simulations at the almost physical point.

hep-lat↗

arXiv2024

Doubly charmed tetraquark $T_{cc}^+$ in (2+1)-flavor QCD near physical point

We study the doubly charmed tetraquark state $T_{cc}^+$ by the HAL QCD method applied to the $D^*D$ system in $(2+1)$ flavor lattice QCD at nearly physical pion mass, $m_\pi= 146$ MeV. We obtain the attractive potential at all distances in the $S$-wave of the isoscalar $D^* D$ system, whose long distance behavior is well described by the two-pion exchange (TPE), and it generates a virtual pole near $D^* D$ threshold with a pole position $E_{\rm pole} = -59 (^{+53}_{-99}) (^{+2}_{-67})$ keV and an inverse scattering length $1/a_0=0.05(5)(^{+2}_{-2})$ fm$^{-1}$. The virtual pole turns into a loosely bound state pole if the pion mass in the TPE potential is extrapolated to the physical value, $m_\pi =135$ MeV. The potential at the physical pion mass is shown to give a semi-quantitative description of the $D^0 D^0\pi^+$ mass spectrum at the LHCb.

hep-lat↗

arXiv2024

Axial U(1) symmetry near the pseudocritical temperature in $N_f=2+1$ lattice QCD with chiral fermions

We study the $U(1)_A$ anomaly at high temperatures of $N_f=2+1$ lattice QCD with chiral fermions. Gauge ensembles are generated with M\"obius domain-wall (MDW) fermions, and the measurements are reweighted to those with overlap fermions. We report on the results for the Dirac spectra, the $U(1)_A$ susceptibility, and the topological susceptibility in the temperature range of $T=136$, $153$, $175$, and $204$ MeV, where the up and down quark masses are set to be near the physical point as well as at lighter or heavier masses.

hep-lat↗

arXiv2024

Study of Chiral Symmetry and $U(1)_A$ using Spatial Correlators for $N_f=2+1$ QCD at finite temperature with Domain Wall Fermions

Based on simulations of 2+1 flavor lattice QCD with M\"obius domain wall fermions at high temperatures, we compute a series of spatial correlation functions to study the screening masses in mesonic states. We compare these masses with the symmetry relations for various quark masses and lattice sizes at temperatures above the critical point. Using these spatial correlation functions we examine the $SU(2)_L \times SU(2)_R$ symmetry as well as the anomalously broken axial $U(1)_A$ symmetry. Additionally we explore a possible and emergent chiral-spin symmetry $SU(2)_{CS}$.

hep-lat↗

arXiv2023

Geometric conservation in curved spacetime and entropy

We provide an improved definition of new conserved quantities derived from the energy-momentum tensor in curved spacetime by introducing an additional scalar function. We find that the conserved current and the associated conserved charge become geometric under a certain initial condition of the scalar function, and show that such a conserved geometric current generally exists in curved spacetime. Furthermore, we demonstrate that the geometric conserved current agrees with the entropy current in an effective theory of a perfect fluid, thus the conserved charge is the total entropy of the system. While the geometric charge can be regarded as the entropy for a nondissipative fluid, its physical meaning should be investigated for more general cases.

hep-th↗