Toru Kojo
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View article: Thermal Quarks and Polyakov Loops in Two-Color Dense QCD
Thermal Quarks and Polyakov Loops in Two-Color Dense QCD Open
We study confinement and deconfinement in dense two-color QCD by analyzing the dynamics of thermal quarks and gluons. The Polyakov loop is used as a probe of the relevant thermal excitations, distinguishing quark- and hadron-dominated regi…
View article: Thermal quarks and Polyakov loops in two-color dense QCD
Thermal quarks and Polyakov loops in two-color dense QCD Open
We study confinement and deconfinement in dense two color QCD by analyzing the dynamics of thermal quarks and gluons. The Polyakov loop is used as a probe of the relevant thermal excitations, distinguishing quark and hadron dominated regim…
View article: Neutron-quark Stars: Discerning Viable Alternatives for the Higher-density Part of the Equation of State of Compact Stars
Neutron-quark Stars: Discerning Viable Alternatives for the Higher-density Part of the Equation of State of Compact Stars Open
We investigate binary neutron star (BNS) mergers using general-relativistic numerical simulations with hadronic and hybrid equations of state (EOSs), incorporating the latest observations and theoretical constraints. We address two viable …
View article: Tripling Fluctuations and Peaked Sound Speed in Fermionic Matter
Tripling Fluctuations and Peaked Sound Speed in Fermionic Matter Open
A crossover involving three-fermion clusters is relevant to the hadron-quark crossover, which, if occurring in a neutron star, could naturally reproduce the dense-matter equation of state recently deduced from simultaneous observations of …
View article: Quarkyonic solution to the hyperon puzzle
Quarkyonic solution to the hyperon puzzle Open
We show that Quarkyonic Matter can mitigate the hyperon puzzle. The key observation is that the hyperon threshold is shifted to a higher density by a factor of constituent strange quark mass. We illustrate this effect by using the ideal du…
View article: Tripling Fluctuations and Peaked Sound Speed in Fermionic Matter
Tripling Fluctuations and Peaked Sound Speed in Fermionic Matter Open
A crossover involving three-fermion clusters is relevant to the hadron-quark crossover, which, if occurring in a neutron star, could naturally reproduce the dense-matter equation of state recently deduced from simultaneous observations of …
View article: Quarkyonic matter pieces together the hyperon puzzle
Quarkyonic matter pieces together the hyperon puzzle Open
Matter composed of hyperons has been hypothesized to occur in neutron stars at densities slightly above the nuclear saturation density and in many descriptions gives rise to a significant softening in the equation of state (EoS). This soft…
View article: Thermal effects on sound velocity peak and conformality in isospin QCD
Thermal effects on sound velocity peak and conformality in isospin QCD Open
We study thermal effects on equations of state (EOS) in isospin QCD, utilizing a quark-meson model coupled to a Polyakov loop. The quark-meson model is analyzed at one-loop that is the minimal order to include quark substructure constraint…
View article: Parity doublet model for baryon octets: Ground states saturated by good diquarks and the role of bad diquarks for excited states
Parity doublet model for baryon octets: Ground states saturated by good diquarks and the role of bad diquarks for excited states Open
Parity doublet model is an effective chiral model that includes the chiral-variant and -invariant masses of baryons. The chiral-invariant mass has large impacts on the density dependence of models which can be constrained by neutron star o…
View article: Neutron-quark stars: Discerning viable alternatives for the higher-density part of the equation of state of compact stars
Neutron-quark stars: Discerning viable alternatives for the higher-density part of the equation of state of compact stars Open
We investigate binary neutron star (BNS) mergers using general-relativistic numerical simulations with hadronic and hybrid equations of state (EOSs), incorporating the latest observations and theoretical constraints. We address two viable …
View article: Isospin QCD as a Laboratory for Dense QCD
Isospin QCD as a Laboratory for Dense QCD Open
QCD with the isospin chemical potential μI is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscop…
View article: Isospin QCD as a laboratory for dense QCD
Isospin QCD as a laboratory for dense QCD Open
QCD with the isospin chemical potential, $μ_I$, is a useful laboratory to delineate the microphysics in dense QCD. To study the quark-hadron-continuity we use a quark-meson model that interpolates hadronic and quark matter physics at micro…
View article: Theoretical and experimental constraints for the equation of state of dense and hot matter
Theoretical and experimental constraints for the equation of state of dense and hot matter Open
This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effect…
View article: Sound velocity peak and conformality in isospin QCD
Sound velocity peak and conformality in isospin QCD Open
We study zero temperature equations of state (EOS) in isospin QCD within a quark-meson model which is renormalizable and hence eliminates high density artifacts in models with the ultraviolet cutoff (e.g., Nambu-Jona-Lasinio type models mo…
View article: Parity doublet model for baryon octets: ground states saturated by good diquarks and the role of bad diquarks for excited states
Parity doublet model for baryon octets: ground states saturated by good diquarks and the role of bad diquarks for excited states Open
Parity doublet model is an effective chiral model that includes the chiral variant and invariant masses of baryons. The chiral invariant mass has large impacts on the density dependence of models which can be constrained by neutron star ob…
View article: Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD
Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD Open
We present a model of cold QCD matter that bridges nuclear and quark matter through the duality relation between quarks and baryons. The baryon number and energy densities are expressed as functionals of either the baryon momentum distribu…
View article: Thermal effects on sound velocity peak and conformality in isospin QCD
Thermal effects on sound velocity peak and conformality in isospin QCD Open
We study thermal effects on equations of state (EOS) in isospin QCD, utilizing a quark-meson model coupled to a Polyakov loop. The quark-meson model is analyzed at one-loop that is the minimal order to include quark substructure constraint…
View article: Parity doublet model for baryon octets: Diquark classifications and mass hierarchy based on the quark-line diagram
Parity doublet model for baryon octets: Diquark classifications and mass hierarchy based on the quark-line diagram Open
We construct ${\mathrm{SU}(3)}_{\mathrm{L}}\ensuremath{\bigotimes}{\mathrm{SU}(3)}_{\mathrm{R}}$ invariant parity doublet models within the linear realization of the chiral symmetry. Describing baryons as the superposition of linear repres…
View article: Universality in quasinormal modes of neutron stars with quark-hadron crossover
Universality in quasinormal modes of neutron stars with quark-hadron crossover Open
We examine the gravitational wave frequencies of the fundamental ($f$-) and 1st pressure ($p_1$-) modes excited in the neutron star models constructed with the quark-hadron crossover (QHC) type equations of state (EOS). We find that the $f…
View article: Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD
Momentum Shell in Quarkyonic Matter from Explicit Duality: A Dual Model for Cold, Dense QCD Open
We present a model of cold QCD matter that bridges nuclear and quark matter through the duality relation between quarks and baryons. The baryon number and energy densities are expressed as functionals of either the baryon momentum distribu…
View article: Sound velocity peak and conformality in isospin QCD
Sound velocity peak and conformality in isospin QCD Open
We study zero temperature equations of state (EOS) in isospin QCD within a quark-meson model which is renormalizable and hence eliminates high density artifacts in models with the ultraviolet cutoff (e.g., NJL models). The model exhibits a…
View article: Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter
Theoretical and Experimental Constraints for the Equation of State of Dense and Hot Matter Open
This review aims at providing an extensive discussion of modern constraints relevant for dense and hot strongly interacting matter. It includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effect…
View article: Chiral Restoration of Nucleons in Neutron Star Matter: Studies Based on a Parity Doublet Model
Chiral Restoration of Nucleons in Neutron Star Matter: Studies Based on a Parity Doublet Model Open
We review the chiral variant and invariant components of nucleon masses and the consequence of their existence on the chiral restoration in extreme conditions, particularly in neutron star matter. We consider a model of linear realization …
View article: Merger and Postmerger of Binary Neutron Stars with a Quark-Hadron Crossover Equation of State
Merger and Postmerger of Binary Neutron Stars with a Quark-Hadron Crossover Equation of State Open
Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOS) are studied for the first time. In contrast to EOS with purely hadronic matter or with a first-order quark-h…
View article: Meson resonance gas in a relativistic quark model: scalar vs vector confinement and semishort range correlations
Meson resonance gas in a relativistic quark model: scalar vs vector confinement and semishort range correlations Open
Smooth transitions from hadronic matter to hot and dense matter of quantum chromodynamics accompany continuous transformations in effective degrees of freedom. The microscopic descriptions should include relativistic quarks interacting ins…
View article: Chiral condensates for neutron stars in hadron-quark crossover; from a parity doublet nucleon model to an NJL quark model
Chiral condensates for neutron stars in hadron-quark crossover; from a parity doublet nucleon model to an NJL quark model Open
In this contribution, we summarize our recent studies on the chiral invariant mass and the chiral condensates in neutron star matter. We construct a unified equations of state assuming the crossover phase transition from hadronic matter de…
View article: Impacts of anomaly on nuclear and neutron star equation of state based on a parity doublet model
Impacts of anomaly on nuclear and neutron star equation of state based on a parity doublet model Open
We examine the role of the $U(1)_A$ anomaly in a parity doublet model of nucleons which include the chiral variant and invariant masses. Our model expresses the $U(1)_A$ anomaly by the Kobayashi-Maskawa-'t\,Hooft (KMT) interaction in the m…
View article: Implications of NICER for Neutron Star Matter: The QHC21 Equation of State
Implications of NICER for Neutron Star Matter: The QHC21 Equation of State Open
The recent NICER measurement of the radius of the neutron star PSR J0740+6620, and the inferred small variation of radii from 1.4 to 2.1 M ⊙ , reveal key features of the equation of state of neutron star matter. The pressure rises rapidly …
View article: Equation of state in neutron stars and supernovae
Equation of state in neutron stars and supernovae Open
Neutron stars and supernovae provide cosmic laboratories of highly compressed matter at supra nuclear saturation density which is beyond the reach of terrestrial experiments. The properties of dense matter is extracted by combining the kno…