arXiv subjects

Hiroaki Abuki

Publications and source records attributed to Hiroaki Abuki.

At least 19 recordsLinked to original sources

arXiv2026

Kaon gravitational form factors and mechanical structure in a three-flavor NJL model

We investigate the gravitational form factors (GFFs) of the kaon in a proper-time-regularized three-flavor Nambu--Jona-Lasinio model. We treat the kaon as a light--strange pseudoscalar bound state and evaluate its energy--momentum-tensor matrix element using a dressed quark--graviton vertex. By retaining the interaction-induced contact contribution alongside the quark triangle diagrams, we preserve the gravitational Ward--Takahashi identity and ensure the conservation of the total energy--momentum tensor. We determine the light- and strange-quark contributions to the kaon GFFs, contrast them with the corresponding pion results, and extract the associated pressure and shear-force distributions, together with the Breit-frame and transverse light-front mass radii. Explicit flavor-symmetry breaking dictates that the strange sector carries a larger share of the kaon momentum and mechanical response. Consequently, compared to the pion, the kaon exhibits a less negative $D$-term and more compact mechanical distributions, featuring enhanced central pressure and shear. We further show that a Ward--Takahashi-identity-preserving reduction of the $C$-term projection is essential for maintaining the pion low-energy theorem in proper-time regularization.

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arXiv2025

Gravitational form factors of the baryon octet in holographic QCD

The gravitational form factors (GFFs) of the baryon octet, including hyperons, are investigated in a bottom-up holographic QCD model that explicitly incorporates the SU(3) flavor symmetry breaking through the strange quark mass. We fit the model parameters to reproduce the empirical masses of the baryon octet and examine the dependence of GFFs on the probe momentum. Our numerical results show distinct differences in the GFFs across the baryon octet. The computed GFFs are found to be in reasonable agreement with available lattice QCD results for the non-strange/nucleon sector. We also calculate the gravitational radii of the baryon octet and find that they decrease with increasing strangeness, indicating that heavier hyperons are more compact.

hep-ph↗

arXiv2021

Transport properties in magnetized compact stars

Transport properties of dense quark matter are discussed in the strong magnetic field, B. B dependence as well as density dependence of the Hall conductivity is discussed in the inhomogeneous chiral phase. Anomalous Hall effect is intrinsic to the inhomogeneous chiral phase and resembles the one in Weyl semimetals in condensed matter physics. Some theoretical aspects inherent in anomalous Hall effect are revealed.

hep-ph↗

arXiv2020

Transport properties in magnetized compact stars

Transport properties of dense QCD matter is discussed. Using the Kubo formula for conductivity, we discuss some topological aspects of quark matter during chiral transition. The close relation to Weyl semimetal is pointed out and anomalous Hall effect is demonstrated to be possible there. In particular, it is shown that the spectral asymmetry of the quasi-particles plays an important role for the Hall conductivity in the magnetic field.

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arXiv2018

Dual chiral density waves in nuclear matter

We study inhomogeneous chiral phases in nuclear matter using a hadronic model with the parity doublet structure. With an extended ansatz for the dual chiral density wave off the chiral limit, we numerically determine the phase structure. A new type of dual chiral density wave where the condensate has nonvanishing space average is confirmed and it comes to occupy a wide range of low density region as the chiral invariant mass parameter is lowered.

hep-ph↗

arXiv2018

Chiral crystallization in an external magnetic background - Chiral spiral versus Real kink crystal -

We study how an external magnetic field modifies the chiral phase structure of QCD, in particular the phases characterized by inhomogeneous chiral condensates. The magnetic field can be systematically incorporated into a generalized Ginzburg-Landau framework, and it turns out to induce a model independent universal coupling between the magnetic field and the axial isospin current. The resulting effect is found to be drastic especially in the chiral limit; no matter how small the magnetic intensity is, the tricritical Lifshitz point is totally washed out, and the real kink crystal is replaced by a magnetically induced chiral spiral. The current quark mass, on the other hand, has an opposite effect, protecting the chiral critical point from the magnetically induced chiral spiral. But once the magnetic intensity exceeds a critical value, the critical point no longer exists. We draw a semiquantitative conclusion that the critical point disappears for $\sqrt{eB}\geq 50$ MeV.

hep-ph↗

arXiv2018

A novel Dual Chiral Density Wave in nuclear matter based on a parity doublet structure

We study the Dual Chiral Density Wave (DCDW) in nuclear matter using a hadronic model with the parity doublet structure. We first extend the ordinary DCDW ansatz so as to incorporate the effect of an explicit chiral symmetry breaking. Then via numerically evaluating and minimizing the effective potential, we determine the phase structure. We find, in addition to the ordinary DCDW phase where the space average of the chiral condensate vanishes, a new DCDW phase (sDCDW) with a nonvanishing space average depending on the value of the chiral invariant mass parameter.

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arXiv2015

Inhomogeneous chiral phases in two-flavor quark matter

We present a systematic study of the phase structure of QCD in a generalized Ginzburg-Landau framework. We find, going up in density, a strongly interacting matter might go through the "pion crystal", an exotic inhomogeneous chiral phase before reaching the full restoration of symmetry.

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arXiv2013

Fate of chiral critical point under the strong isospin asymmetry

We study the influence of the isospin asymmetry on the phase structure of strongly interacting quark matter near the critical point (CP) using a Ginzburg-Landau approach. The effect is found to be drastic, not only bringing about the shift of the location of the CP, but resulting in a rich phase structure in the vicinity of the CP. In particular, new tricritical and triple points emerge as soon as the isospin density becomes finite. Moreover, we find the CP being washed out from the phase diagram due to the stabilization of a homogeneous charged pion condensate when the isospin chemical potential exceeds a critical value. We derive a model-independent universal relation between the critical isospin chemical potential and the chiral condensate at the CP. We also study the effect of the $\mathrm{U}(1)_\mathrm{A}$ anomaly on the phase transition to the pion condensate in the vicinity of chiral crossover.

hep-ph↗

arXiv2012

Chiral multicritical points driven by isospin density in the Ginzburg-Landau approach

We study how a chiral tricritical point (TCP) on QCD phase diagram is affected by the imbalance of up and down quark densities (isospin density), using the generalized Ginzburg-Landau (GL) approach. The resulting phase diagram near TCP shows a rich fine structure which includes inhomogeneities of both the chiral and the charged pion condensations. It turns out that the TCP splits into multicritical points.

hep-ph↗

arXiv2012

Ginzburg-Landau approach to inhomogeneous chiral phases of QCD

We study the inhomogeneous chiral condensates in the proximity of the chiral tricritical point (TCP) of two-flavor QCD. Deriving the Ginzburg-Landau (GL) functional up to the eighth order in the order parameter and its spatial derivative, we explore off the TCP and find that critical curves are bent by non-linear effects. In the newly extend GL coupling space, we find the TCP being realized as a multicritical point where five independent critical lines meet up. We also present general analyses for the energies associated with several higher dimensional crystal structures.

hep-ph↗

arXiv2012

Splitting of the chiral critical point and realization of solitonic pion condensate driven by isospin density

We study the influence of the isospin asymmetry on the phase structure of strongly interacting quark matter near the tricritical point (TCP) using a generalized Ginzburg-Landau approach. The effect has proven to be so drastic, not only bringing about the shift of the location of TCP, but resulting in a rich fine structure at the vicinity of TCP. In particular, we find that an arbitrary small perturbation due to isospin density lifts the degeneracy of TCP making it split into four independent multicritical points. Accordingly, the homogeneous pion condensate and its solitonic counterpart come to occupy large domains in the Ginzburg-Landau coupling space.

hep-ph↗

arXiv2012

Crystalline chiral condensates off the tricritical point in a generalized Ginzburg-Landau approach

We present an extensive study on inhomogeneous chiral condensates in QCD at finite density in the chiral limit using a generalized Ginzburg-Landau (GL) approach. Performing analyses on higher harmonics of one-dimensionally (1D) modulated condensates, we numerically confirm the previous claim that the solitonic chiral condensate characterized by Jacobi's elliptic function is the most favorable structure in 1D modulations. We then investigate the possibility of realization of several multidimensional modulations within the same framework. We also study the phase structure far away from the tricritical point by extending the GL functional expanded up to the eighth order in the order parameter and its spatial derivative. On the same basis, we explore a new regime in the extended GL parameter space and find that the Lifshitz point is the point where five critical lines meet at once. In particular, the existence of an intriguing triple point is demonstrated, and its trajectory consists of one of those critical lines.

hep-ph↗

arXiv2012

How does color neutrality affect collective modes in color superconductors?

We revisit the issue of color neutrality in effective model descriptions of dense quark matter based on global color symmetry. While the equilibrium thermodynamics of such models is now well understood, we examine the collective modes, focusing on the fluctuations of the order parameter. We point out that the constraint of color neutrality must be carefully generalized in order to obtain physically consistent and well-defined results. Particularly important is that the collective modes associated with order parameter fluctuations couple to charge density fluctuations in the neutral medium. We start by proving explicitly that, in contrast to claims made previously in literature, Nambu-Goldstone bosons of spontaneously broken global color symmetry remain exactly massless even after imposing the color neutrality constraint. As the next step, we make the argument general by using effective field theory. We then employ the high-density approximation to calculate the couplings in the effective Lagrangian and thus the Nambu-Goldstone boson dispersion relations.

hep-ph↗

arXiv2010

Transport coefficients of causal dissipative relativistic hydrodynamics in quenched lattice simulations

Transport coefficients of causal dissipative relativistic fluid dynamics (CDR) are studied in quenched lattice simulations. CDR describes the behavior of relativistic non-Newtonian fluids in which the relaxation time appears as a new transport coefficient besides the shear and bulk viscosities. It was recently shown that these coefficients can be given by the temporal-correlation functions of the energy-momentum tensors as in the case of the Green-Kubo-Nakano formula. By using the new formula in CDR, we study the transport coefficients with lattice simulations in pure SU(3) gauge theory. After defining the energy-momentum tensor on the lattice, we extract a ratio of the shear viscosity to the relaxation time which is given only in terms of the static correlation functions. The simulations are performed on $24^3 \times 4$--16 lattices with $β_{_{\rm LAT}} = 6.0$, which corresponds to the temperature range of $0.5 \simle T/T_c \simle 1.8$, where $T_c$ is the critical temperature.

hep-lat↗

arXiv2010

BEC-BCS crossover driven by the axial anomaly in the NJL model

We study the QCD phase structure in the three-flavor Nambu--Jona-Lasinio model, incorporating the chiral-diquark interplay due to the axial anomaly. We demonstrate that for a certain range of model parameters, the low temperature critical point predicted by a Ginzburg-Landau analysis appears in the phase diagram. In addition, we show that the axial anomaly presents a new scenario for a possible BEC-BCS crossover in the color-flavor locked phase of QCD.

hep-ph↗

arXiv2010

The NJL model of dense three-flavor matter with axial anomaly: the low temperature critical point and BEC-BCS diquark crossover

We study the QCD phase structure in the three-flavor Nambu-Jona-Lasinio model, incorporating the interplay between the chiral and diquark condensates induced by the axial anomaly. We demonstrate that for an appropriate range of parameters of the model, the interplay leads to the low temperature critical point in the phase structure predicted by a previous Ginzburg-Landau analysis. We also show that a Bose-Einstein condensate (BEC) of diquark molecules emerges in the intermediate density region, and as a result, a BEC-BCS crossover is realized with increasing quark chemical potential.

hep-ph↗

arXiv2009

Pion condensation in a dense neutrino gas

We argue that using an equilibrated gas of neutrinos it is possible to probe the phase diagram of QCD for finite isospin and small baryon chemical potentials. We discuss this region of the phase diagram in detail and demonstrate that for large enough neutrino densities a Bose-Einstein condensate of positively charged pions arises. Moreover, we show that for nonzero neutrino density the degeneracy in the lifetimes and masses of the charged pions is lifted.

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