arXiv subjects

Mamiya Kawaguchi

Publications and source records attributed to Mamiya Kawaguchi.

At least 19 recordsLinked to original sources

arXiv2026

Meson gravitational D-form factors and symmetry breaking in low-energy QCD

We investigate meson gravitational D-form factors in the three-flavor linear sigma model and their connection to symmetry breaking in low-energy QCD. Within the scalar meson dominance picture, we examine the scalar meson exchange contributions and their relation to meson masses through scalar-meson couplings. In the three-flavor symmetric limit, we first derive analytical expressions for the D-form factors of pseudoscalar and scalar mesons. In the chiral limit, the forward-limit value of the octet pseudoscalar D-form factor is fixed to $-1$, whereas the $U(1)_A$ anomaly generates additional contributions to the singlet pseudoscalar and scalar-meson D-form factors. For realistic flavor breaking, the interaction introduced to reproduce the scalar-meson mass hierarchy below $1$ GeV significantly affects the scalar-meson D-form factors. We further compare the linear sigma model results with those obtained from a chiral perturbation theory Lagrangian including a dilatonic scalar field and show that their differences are governed by the canonical mass dimensions of the interaction terms contributing to meson mass generation. These results indicate that meson D-form factors provide sensitive probes of symmetry-breaking structures in low-energy hadron physics.

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arXiv2026

Charmonium-nucleon femtoscopy as a possible probe of the nucleon gravitational form factor

We investigate the charmonium-nucleon interaction, focusing on its connection with the internal structure of the nucleon encoded in the gravitational form factors. To describe this interaction, we employ an effective potential based on the QCD multipole expansion within the leading chromoelectric dipole approximation. In this framework, the potential is expressed in terms of the energy and pressure distributions inside the nucleon. We first construct these distributions from the gravitational form factors fitted to lattice-QCD data. The remaining model parameters are then fixed by requiring that the resulting $J/\psi$-$N$ potential reproduce the HAL QCD potential outside the short-distance region, as well as the scattering phase shift estimated from the HAL QCD data. Based on this potential, we evaluate the $J/\psi$-$N$ correlation function and further investigate the $\psi(2S)$-$N$ system. We then examine the sensitivity of these correlation functions to the nucleon $D$-form factor.

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arXiv2026

Thermodynamics in symmetry-improved Cornwall-Jackiw-Tomboulis formalism: application to the low-energy effective theory of QCD

We study the thermodynamics of the symmetry-improved Cornwall-Jackiw-Tomboulis (SICJT) formalism and apply it to a low-energy effective theory of QCD. In the symmetry-improved formulation, Ward-Takahashi identities are restored by auxiliary sources whose values are fixed self-consistently by the equilibrium state. While this construction improves the symmetry properties of the loop-wise truncated two-particle-irreducible (2PI) theory, it also makes the thermodynamic interpretation of the pressure nontrivial. We formulate several pressure prescriptions, including the conventional vacuum-subtracted pressure, a source-matched subtraction, and a pulled-back pressure in which the explicit source-induced energy shift is removed. Using the three-flavor linear sigma model with quarks, we analyze the equation of state, isentropic trajectories, adiabatic sound velocity, and trace anomaly across the chiral transition. We find that the global thermodynamic structure is stable under the different prescriptions, while quantitative differences are concentrated near the crossover and first-order transition region. These results establish a practical framework for constructing thermodynamically consistent observables in symmetry-improved 2PI approaches.

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arXiv2026

Probing the chiral and $U(1)$ axial symmetry restoration via meson susceptibilities in holographic QCD

We investigate the restoration patterns of chiral and $U(1)$ axial symmetries at finite temperature using a soft-wall holographic QCD model. The study employs two distinct parameter sets (Case I and Case II), both calibrated to reproduce a pseudocritical temperature $T_{\rm pc} \sim 155$ MeV and the physical pion mass. The temperature dependence of the light and strange quark condensates confirms a smooth chiral crossover transition, with pseudocritical temperatures of $T_{\rm pc}=0.157$ GeV and $T_{\rm pc}=0.154$ GeV for Cases I and II, respectively. The screening masses of chiral partner mesons ($\pi$-$\sigma$ and $\eta$-$a_0$) become degenerate near $T_{\rm pc}$, providing a clear signature of chiral symmetry restoration. Analysis of the corresponding meson susceptibilities further supports this conclusion. However, the indicator for $U(1)$ axial symmetry restoration, $\chi_\pi - \chi_{a_0}$, vanishes at a temperature $T \sim 0.190 $ GeV, which indicates a distinct restoration scale with chiral symmetry restoration scale within the present holographic framework. The temperature-dependent topological susceptibility $\chi_{\rm top}^{1/4}$ is also computed, showing a sharp drop near $T_{\rm pc}$ and a subsequent slight decrease. While the model qualitatively captures established features of the chiral transition, the results highlight a limitation in the qualitative description of the $U(1)$ axial anomaly compared to LQCD in our work.

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arXiv2025

Origin of hadron mass from gravitational D-form factor and neutron star measurements

Clarifying the origin of hadron mass is one of the fundamental problems in particle physics, relevant from hadronic scales to astrophysical observations. At low energies, this issue is reflected in the decomposition of the hadron mass into chiral-variant and -invariant components. In this letter, we propose a method to extract the chiral invariant mass from the gravitational $D$-form factor under the assumption of the lightest-sigma meson dominance. Focusing on the nucleon, we show that a sizable chiral invariant mass is required to reproduce lattice QCD data, consistent with neutron star constraints.

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arXiv2025

Susceptibilities of rotating quark matter in Fourier-Bessel basis

We analyze various two-point correlation functions of fermionic bilinears in a rotating finite-size cylinder at finite temperatures, with a focus on susceptibility functions. Due to the noninvariance of radial translation, the susceptibility functions are constructed using the Dirac propagator in the Fourier-Bessel basis instead of the plane-wave basis. As a specific model to demonstrate the susceptibility functions in an interacting theory, we employ the two-flavor Nambu-Jona-Lasinio model. We show that the incompatibility between the mean-field analysis and the Fourier-Bessel basis is evaded under the local density approximation, and derive the resummation formulas of susceptibilities with the help of a Ward-Takahashi identity. The resulting formulation reveals the rotational effects on meson, baryon number, and topological susceptibilities, as well as the moment of inertia. Our results may serve a useful benchmark for future lattice QCD simulations in rotating frames.

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arXiv2025

Gravitational form factors of the nucleon from the chiral effective model

We investigate the confining pressure and associated global property, i.e, D-term, of the nucleon using the skyrmion approach formulated within scale-invariant chiral perturbation theory. In this framework, the nucleon is modeled as a skyrmion, and a scalar meson is introduced to incorporate the effects of the scale anomaly via low-energy theorems. The contributions from the current quark mass and gluonic dynamics to the scale anomaly are encoded through the pion and scalar meson masses, respectively. By decomposing the nucleon's energy-momentum tensor, we isolate the anomalous components and analyze their role in generating pressure. We find that the gluonic contribution to the scale anomaly plays a dominant role in producing confining pressure. In comparison with results from conventional chiral perturbation theory in the chiral limit, the total pressure derived from sChPT provides improved qualitative agreement with lattice QCD results. We also evaluate the D-term and compare it with recent lattice and model-independent determinations.

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arXiv2025

Columbia plot based on symmetry-improved CJT formalism in linear sigma model

We study the Columbia plot for the chiral phase transition in the framework of a three-flavor linear sigma model based on the Cornwall-Jackiw-Tomboulis (CJT) formalism. The conventional CJT approach with the Hartree truncation suffers from artificial chiral breaking, leading to the violation of the Nambu-Goldstone theorem and the (anomalous) chiral Ward-Takahashi identities. We apply the symmetry-improved CJT formalism to resolve this issue. We observe a first-order phase transition and a tricritical point in the light-quark mass regime, which is fairly insensitive to the size of the sigma meson, in contrast to the conventional CJT approach. The tricritical point, found on the $m_s$ axis, is at $m_s^{\rm tri}/m_s^{\rm phys.} = 0.175$ with $m_s^{\rm phys.}$ being the physical strange quark mass in real-life QCD. The critical pion mass in the three-flavor symmetric limit, on the second-order boundary, is measured at $m_\pi \sim 52.4$ MeV, with the critical temperature $T_c \sim 51.7$ MeV.

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arXiv2025

Dominance of gluonic scale anomaly in confining pressure inside nucleon and D-term

We explore the confining pressure inside the nucleon and the related gravitational form factor referred to as the D-term, using the skyrmion approach based on the scale-invariant chiral perturbation theory, where the skyrmion is described as the nucleon and a scalar meson couples to the scale anomaly through the low energy theorem. Within this model framework, the current quark mass and gluonic quantum contributions to the scale anomaly can be described by the pion and scalar meson masses, respectively, through matching with the underlying QCD. By considering the decomposition of the energy momentum tensor of nucleon, we examine the role of the scale anomaly contributions in the pressure inside the nucleon. As a result, the gluonic scale anomaly is found to dominate the confining pressure. Compared to the result based on the conventional chiral perturbation theory in the chiral limit, our result for the total pressure is capable of qualitatively improving the alignment with lattice QCD observations. Moreover, the pressure from the gluonic scale anomaly is widely distributed in position space, leading to its substantial contribution to the D-term.

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arXiv2025

Gravitational form factors of the nucleon in the Skyrme model based on scale-invariant chiral perturbation theory

We investigate the role of the QCD scale anomaly in the gravitational form factors of the nucleon -- particularly the $D(t)$ form factor -- as well as the associated stress distribution and internal forces, using a Skyrme model based on the scale-invariant chiral perturbation theory. A distinctive feature of this model is the inclusion of both the pion and the scalar meson, which respectively capture the effects of the current quark mass and gluonic quantum contributions to the scale anomaly. By varying the mass of the scalar meson, we evaluate the sensitivity of the gluonic scale anomaly to the nucleon properties. We find that the gluonic scale anomaly plays a crucial role in satisfying the stability conditions of the nucleon and provides an internal confining force. Moreover, we also evaluate the momentum-transfer dependence of $D(t)$, which closely reproduces the lattice QCD results. With an appropriate choice of the anomalous dimension associated with the quark mass, its forward-limit value (i.e., the D-term) also matches the lattice data well.

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arXiv2025

Axionlike particle-assisted supercooling chiral phase transition in QCD: Identifying Coleman-Weinberg type-chiral phase transition in QCD-like scenarios

We propose a new scenario to realize the Coleman-Weinberg (CW) type chiral phase transition in the QCD thermal history. This scenario predicts a heavy axionlike particle (ALP) with mass $\sim$ 5 MeV, consistently with the current experimental and cosmological bounds. The chiral phase transition is evaluated by monitoring ordinary QCD setup in a view of a two-flavor Nambu-Jona-Lasinio model including a simplified meson fluctuation contribution. The present work thus can open a new window to search for the ALP associated with the QCD phase transition epoch of the thermal history. The new QCD cosmological scenario potentially predicts rich epochs around the QCD scale: a mini-inflation; a nonperturbative preheating and/or reheating, which can provide characteristic gravitational wave and primordial black hole productions. This proposal is based on a generic classification of the order of the chiral phase transition at the level of the mean field approximation in view of the scale violation classes: the soft-scale breaking term and the CW-type scale anomaly term, in or off the medium with or without chemical potentials. On this theoretical ground, we also revisit existing scenarios which undergo the supercooling chiral phase transition, such as nearly scale-invariant QCD and QCD with a large baryon chemical potential.

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arXiv2025

Implications of electromagnetic scale anomaly to QCD chiral phase transition in smaller quark mass regime: $T_{\mathrm{pc}}$ does not drop with eB

The decrease of the chiral pseudocritical temperature $T_{\mathrm{pc}}$ with an applied strong magnetic field has been extensively investigated by various QCD low-energy effective models and lattice QCD at physical point. We find that this decreasing feature may not hold in the case with a weak magnetic field and still depends on quark masses: when the quark masses get smaller, $T_{\mathrm{pc}}$ turns to increase with the weak magnetic field. This happens due to the significant electromagnetic-scale anomaly contribution in the thermomagnetic medium. We demonstrate this salient feature by employing the Nambu-Jona-Lasinio model with 2 + 1 quark flavors including the electromagnetic-scale anomaly contribution. We observe that at $(m_{0c}, m_{sc}) \simeq (2, 20) \mathrm{MeV}$ for the isospin symmetric mass for up and down quarks, $m_0$, and the strange quark mass, $m_s$, $T_{\mathrm{pc}}$ decreases with the magnetic field if the quark masses exceed the critical values, and increases as the quark masses become smaller. Related cosmological implications, arising when the supercooled electroweak phase transition or dark QCD cosmological phase transition is considered along with a primordial magnetic field, are also briefly addressed.

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arXiv2025

Functional renormalization group study of a four-fermion model with $CP$ violation

We perform a functional renormalization group analysis of a four-fermion model with $CP$ and $P$ violation to explore the nonperturbative infrared dynamics of quantum chromodynamics (QCD) within the Wilsonian renormalization group framework, particularly in the context of spontaneous $CP$-violation models. Our analysis of the fixed-point structure reveals that, in the large-$N_c$ limit, the $CP$-violating $\barθ$ parameter is dynamically induced and approaches $π\cdot (N_f/2)$ (where $N_f$ is the number of flavors) as the system enters the chirally broken phase. This behavior arises due to criticality and the large anomalous dimensions of the $U(1)_A$-violating four-fermion couplings. Furthermore, this trend appears to persist beyond the leading large-$N_c$ approximation, provided that the infrared dynamics of QCD remains dominated by the scalar condensate of the quark bilinear, as expected. Notably, our findings highlight that $CP$-violating four-fermion interactions, which are perturbatively irrelevant, can become relevant in the chirally broken phase through nonperturbative effects, with potential implications for spontaneous $CP$-violation scenarios.

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arXiv2025

First-order CP phase transition in two-flavor QCD at $θ= π$ under electromagnetic scale anomaly via a Nambu-Jona-Lasinio description

We discuss the thermal CP phase transition in QCD at $θ=π$ under a weak magnetic field background, where the electromagnetic scale anomaly gets significant. To explicitize, we work on a two-flavor Nambu-Jona-Lasinio model at $θ=π$ in the mean field approximation, including the electromagnetic-scale anomaly term. We find that the thermal CP phase transition becomes first order and the strength of the first order gets more prominent as the magnetic field increases. The associated potential barrier is thermally created by the electromagnetic scale anomaly and gives rise to criticality due to the induced potential of a non-perturbative form $\sim \frac{|eB|^3}{f_π} \frac{|P|}{P^2 + m_0^2}$, where $eB$ denotes the magnetic field strength; $P$ the CP order parameter, and $m_0$ the isospin-symmetric current-quark mass.

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arXiv2024

The effect of charm quark on chiral phase transition in $N_f=2+1+1$ holographic QCD

We investigate the effect of charm quark on the chiral phase transition of light quarks at finite temperature based on the four-flavor soft-wall holographic QCD model. In the massless limit, we find that the thermal chiral phase transition is of the second order in the four-quark flavor system. In the case with the massive charm quark and the massless light and strange quarks, the order of the phase transition changes to the first order. This is due to the quark flavor symmetry breaking which is associated with the violation of the $U(1)$ axial symmetry. Once the light and strange quarks get massive, the explicit chiral symmetry breaking becomes eminent, then the crossover phase transition is realized at the physical quark masses. We also map the order of the phase transition on a phase diagram in the quark mass plane where the light- and strange-quark masses are degenerate but differ from the value of the charm quark mass. This phase diagram is an extension of the conventional Columbia plot to the four-quark flavor system. The critical exponents related to the chiral phase transition are also addressed.

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arXiv2024

Effect of quark anomalous magnetic moment on neutral dense quark matter under magnetic field

We discuss the effect of the quark anomalous magnetic moment (AMM) on the neutral dense quark matter under magnetic fields based on the Nambu-Jona-Lasinio (NJL) model at finite baryon density. To address its correlation with the chiral symmetry, we consider a simplified situation: the model includes the two-quark flavors under constant magnetic fields, and incorporates the effective interaction of the quark AMM linked to the spontaneous chiral symmetry breaking. We then examine the equation of state (EoS) in cases with and without magnetization for anatomizing the thermodynamic quantities. Without the magnetization, a small magnetic field stiffens the EoS, but with increasing the magnetic field, the EoS tends to soften. The stiffness of the EoS is found to be influenced by the magnetic effect on the critical chemical potential of the chiral phase transition and the quark number density at this critical point. As a result, the mass and radius of the neutral dense quark matter increase with the small magnetic field but turn to decrease as the magnetic field further increases. By including the quark AMM, the critical chemical potential is decreased and the quark number density takes a smaller value. Thus, for the stronger magnetic fields, the quark AMM suppresses the softening effect of the magnetic field on the EoS, leading to increased mass and radius compared to when the quark AMM is absent. In contrast, for the small magnetic field, the contribution of the quark AMM to the EoS is marginal. When the magnetization is taken into account, the magnetic effect on the stiffness of the EoS is overshadowed by the contribution of the magnetization, and the significance of the quark AMM also becomes invisible in the mass-radius relation.

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arXiv2024

Sound velocity peak induced by the chiral partner in dense two-color QCD

Recently, the peak structure of the sound velocity was observed in the lattice simulation of two-color and two-flavor QCD at the finite quark chemical potential. The comparison with the chiral perturbation theory (ChPT) result was undertaken, however, the ChPT failed in reproducing the peak structure. In this study, to extend the ChPT framework, we incorporate contributions of the $σ$ meson, that is identified as the chiral partner of pions, on top of the low-energy pion dynamics by using the linear sigma model (LSM). Based on the LSM we derive analytic expressions of the thermodynamic quantities as well as the sound velocity within a mean-field approximation. As a result, we find that those quantities are provided by sums of the ChPT results and corrections, where the latter is characterized by a mass difference between the chiral partners, the $σ$ meson and pion. The chiral partner contributions are found to yield a peak in the sound velocity successfully. We furthermore show that the sound velocity peak emerges only when $m_σ>\sqrt{3}m_π$ and $μ_q > m_π$, with $m_{σ(π)}$ and $μ_q$ being the $σ$ meson (pion) mass and the quark chemical potential, respectively. The correlation between the sound velocity peak and the sign of the trace anomaly is also addressed.

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arXiv2024

Impact of local CP-odd domain in hot QCD on axionic domain-wall interpretation for NANOGrav 15-year Data

We argue that the axionic domain-wall with a QCD bias may be incompatible with the NANOGrav 15-year data on a stochastic gravitational wave (GW) background, when the domain wall network collapses in the hot-QCD induced local CP-odd domain. This is due to the drastic suppression of the QCD bias set by the QCD topological susceptibility in the presence of the CP-odd domain with nonzero $θ$ parameter of order one which the QCD sphaleron could generate. We quantify the effect on the GW signals by working on a low-energy effective model of Nambu-Jona-Lasinio type in the mean field approximation. We find that only at $θ=π$, the QCD bias tends to get significantly large enough due to the criticality of the thermal CP restoration, which would, however, give too big signal strengths to be consistent with the NANOGrav 15-year data and would also be subject to the strength of the phase transition at the criticality.

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