Youngman Kim - Profile on Academia.edu (original) (raw)
Papers by Youngman Kim
Physical Review C, 2018
We study the phase structure of dense hadronic matter including ∆(1232) as well as N (939) based ... more We study the phase structure of dense hadronic matter including ∆(1232) as well as N (939) based on the parity partner structure, where the baryons have their chiral partners with a certain amount of chiral invariant masses. We show that, in symmetric matter, ∆ enters into matter in the density region of about one to four times of normal nuclear matter density, ρB ∼ 1-4ρ0. The onset density of ∆ matter depends on the chiral invariant mass of ∆, m∆0: The lager m∆0, the bigger the onset density. The ∆ matter of ρB ∼ 1-4ρ0 is unstable due to the existence of ∆, and the stable ∆-nucleon matter is realized at about ρB ∼ 4 ρ0, i.e., the phase transition from nuclear matter to ∆-nucleon matter is of first order for small m∆0, and it is of second order for large m∆0. We find that, associated with the phase transition, the chiral condensate changes very rapidly, i.e., the chiral symmetry restoration is accelerated by ∆ matter. As a result of the accelerations, there appear N * (1535) and ∆(1700), which are the chiral partners to N (939) and ∆(1232), in high density matter, signaling the partial chiral symmetry restoration. Furthermore, we find that complete chiral symmetry restoration itself is delayed by ∆ matter. We also calculate the effective masses, pressure and symmetry energy to study how the transition to ∆ matter affects such physical quantities. We observe that the physical quantities change drastically at the transition density.
Physical Review C, 2015
We construct a model to describe dense hadronic matter at zero and finite temperature, based on t... more We construct a model to describe dense hadronic matter at zero and finite temperature, based on the parity doublet model of DeTar and Kunihiro, with including the iso-singlet scalar meson σ as well as ρ and ω mesons. We show that, by including a six-point interaction of σ meson, the model reasonably reproduces the properties of the normal nuclear matter with the chiral invariant nucleon mass m0 in the range from 500 MeV to 900 MeV. Furthermore, we study the phase diagram based on the model, which shows that the value of the chiral condensate drops at the liquid-gas phase transition point and at the chiral phase transition point. We also study asymmetric nuclear matter and find that the first order phase transition for the liquid-gas phase transition disappears in asymmetric matter and that the critical density for the chiral phase transition at non-zero density becomes smaller for larger asymmetry.
Journal of High Energy Physics, 2009
We investigate the hybrid exotic meson with J P C = 1 −+ within the framework of an AdS/QCD model... more We investigate the hybrid exotic meson with J P C = 1 −+ within the framework of an AdS/QCD model. Introducing a holographic field dual to the operator for hybrid exotic meson, we obtain the eigen-value equation for its mass. Fixing all free parameters by QCD observables such as the ρ-meson mass, we predict the masses of the hybrid exotic meson. The results turn out to be 1476 MeV for the ground state, and 2611 MeV for the first excited one. Being compared with the existing experimental data for the π 1 (1400), which is known to be m π 1 = 1351 ± 30 MeV, the present result seems to be qualitative in agreement with it. We also predict the decay constant of π 1 (1400): F π 1 = 10.6 MeV.
We study strange and isospin asymmetric matter in a bottom-up AdS/QCD model. We first consider is... more We study strange and isospin asymmetric matter in a bottom-up AdS/QCD model. We first consider isospin matter, which has served as a good testing ground for nonperturbative QCD, to discuss if the model is suitable to describe QCD with various chemical potentials. We calculate the µ I-dependencies of the masses and decay constants of the pion and the vector-meson. We discuss a possibility of the charged pion condensation in the matter within the bottom-up AdS/QCD model. Then we investigate strange matter in the model. We calculate the deconfinement temperature in strange and isospin asymmetric matter. One of the interesting results of our study is that the critical temperature at a fixed baryon number density increases when strangeness chemical potential is introduced. This suggests that if matter undergoes a transition to strange matter, the critical temperature shows a sudden jump at the transition point.
We study a meson mass splitting due to isospin violation in holographic dense matter. We work in ... more We study a meson mass splitting due to isospin violation in holographic dense matter. We work in a D4/D6/D6 model with two quark flavor branes to consider asymmetric dense matter in holographic QCD. We mainly consider two cases. We first consider m+/m−simmd/mum^+/m^-\sim m_d/m_um+/m−simmd/mu to study the effect of isospin violation on the meson masses. Then, we take m+/m−simms/mqm^+/m^-\sim m_s/m_qm+/m−simms/mq, where mqsim(mu+md)/2m_q\sim(m_u+m_d)/2mqsim(mu+md)/2, to calculate in-medium kaon-like meson masses. In both cases we observe that the mass splitting of charged mesons occurs at low densities due to the asymmetry, while at high densities their masses become degenerate. At intermediate densities, we find an exotic behavior in masses which could be partly understood in a simple picture based on the Pauli exclusion principle.
Journal of the Korean Physical Society, 2015
We study the effects of flavor symmetry breaking on holographic dense matter and compact stars in... more We study the effects of flavor symmetry breaking on holographic dense matter and compact stars in the D4/D6 model. To this end, two light flavors and one intermediate mass flavor are considered. For two light quarks, we investigate how the strong isospin violation affects the properties of holographic dense matter and compact stars. We observe that quark-antiquark condensates are flavor dependent and show interesting behavior near the transition from dense matter with only one flavor to matter with two flavors. An intermediate mass quark is introduced to investigate the role of the third flavor. The mass-radius relations of holographic compact stars with three flavors show that the mass-radius curve changes drastically at a transition density from which the third flavor begins to appear in the matter.
Journal of High Energy Physics, 2011
We solve the Tolman-Oppenheimer-Volkoff equation using an equation of state (EoS) calculated in h... more We solve the Tolman-Oppenheimer-Volkoff equation using an equation of state (EoS) calculated in holographic QCD. The aim is to use compact astrophysical objects like neutron stars as an indicator to test holographic equations of state. We first try an EoS from a dense D4/D8/D8 model. In this case, however, we could not find a stable compact star, a star satisfying pressure-zero condition with a radius R, p(R) = 0, within a reasonable value of the radius. This means that the EoS from the D4/D8/D8 model may not support any stable compact stars or may support one whose radius is very large. This might be due to a deficit of attractive force from a scalar field or two-pion exchange in the D4/D8/D8 model. Then, we consider D4/D6 type models with different number of quark flavors, N f = 1, 2, 3. Though the mass and radius of a holographic star is larger than those of normal neutron stars, the D4/D6 type EoS renders a stable compact star.
EPJ Web of Conferences, 2012
We study asymmetric dense matter in holographic QCD. We construct asymmetric dense matter by cons... more We study asymmetric dense matter in holographic QCD. We construct asymmetric dense matter by considering two quark flavor branes with different quark masses in a D4/D6/D6 model. To calculate the symmetry energy in nuclear matter, we consider two quarks with equal masses and observe that the symmetry energy increases with the total charge showing the stiff dependence. This behavior is universal in the sense that the result is independent of parameters in the model. We also study strange (or hyperon) matter with one light and one intermediate mass quarks. In addition to the vacuum properties of asymmetric matter, we calculate meson masses in asymmetric dense matter and discuss our results in the light of in-medium kaon masses.
Journal of High Energy Physics, 2008
We study the quark number susceptibility, an indicator of QCD phase transition, in the hard wall ... more We study the quark number susceptibility, an indicator of QCD phase transition, in the hard wall and soft wall models of hQCD. We find that the susceptibilities in both models are the same, jumping up at the deconfinement phase transition temperature. We also find that the diffusion constant in the soft wall model is enhanced compared to the one in the hard wall model.
Hadron and Nuclear Physics 09, 2010
We present in this talk a recent investigation on a unified approach within the framework of a ha... more We present in this talk a recent investigation on a unified approach within the framework of a hard-wall model of AdS/QCD. We first study a theoretical inconsistency in existing models. In order to remove this inconsistency, we propose a unified approach in which the mesons and the nucleons are treated on the same footing, the same infrared (IR) cutoff being employed in both fermionic and bosonic sectors. We also suggest a possible way of improving the model by introducing a five-dimensional anomalous dimension.
Journal of High Energy Physics, 2008
We investigate the quark-gluon mixed condensate based on an AdS/QCD model. Introducing a holograp... more We investigate the quark-gluon mixed condensate based on an AdS/QCD model. Introducing a holographic field dual to the operator for the quark-gluon mixed condensate, we obtain the corresponding classical equation of motion. Taking the mixed condensate as an additional free parameter, we show that the present scheme reproduces very well experimental data. A fixed value of the mixed condensate is in good agreement with that of the QCD sum rules.
Journal of High Energy Physics, 2009
We investigate masses and coupling constants of mesons and nucleons within a hard wall model of h... more We investigate masses and coupling constants of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. We first examine an appropriate form of fermionic solutions by restricting the mass coupling for the five dimensional bulk fermions and bosons. We then derive approximated analytic solutions for the nucleons and the corresponding masses in a small mass coupling region. In order to treat meson and nucleon properties on the same footing, we introduce the same infrared (IR) cut in such a way that the meson-nucleon coupling constants, i.e., g πN N and g ρN N are uniquely determined. The first order approximation with respect to a dimensionless expansion parameter, which is valid in the small mass coupling region, explicitly shows difficulties to avoid the IR scale problem of the hard wall model. We discuss possible ways of circumventing these problems.
Journal of High Energy Physics, 2010
We study the quark number susceptibility in holographic QCD with a finite chemical potential or u... more We study the quark number susceptibility in holographic QCD with a finite chemical potential or under an external magnetic field at finite temperature. We first consider the quark number susceptibility with the chemical potential. We observe that approaching T c from high temperature regime, χ q /T 2 develops a peak as we increase the chemical potential, which confirms recent lattice QCD results. We discuss this behavior in connection with the existence of the critical end point in the QCD phase diagram. We also consider the quark number susceptibility under the external magnetic field. We predict that the quark number susceptibility exhibits a blow-up behavior at low temperature as we raise the value of the magnetic field. We finally spell out some limitations of our study.
Journal of High Energy Physics, 2010
We construct a simple holographic QCD model to study nuclear matter to strange matter transition.... more We construct a simple holographic QCD model to study nuclear matter to strange matter transition. The interaction of dense medium and hadrons is taken care of by imposing the force balancing condition for stable D4/D6/D6 configuration. By considering the intermediate and light flavor branes interacting with baryon vertex homogeneously distributed along R 3 space and requesting the energy minimization, we find that there is a well defined transition density as a function of current quark mass. We also find that as density goes up very high, intermediate (or heavy) and light quarks populate equally as expected from the Pauli principle. In this sense, the effect of the Pauli principle is realized as dynamics of D-branes.
Progress of Theoretical Physics, 2011
We study the effect of a finite quark mass on the quark number susceptibility in the framework of... more We study the effect of a finite quark mass on the quark number susceptibility in the framework of holographic QCD. We work in a bottom-up model with a deformed AdS black hole and D3/D7 model to calculate the quark number susceptibility at finite temperature with/without a finite quark chemical potential. As expected the finite quark mass suppresses the quark number susceptibility. We find that at high temperatures T ≥ 600 MeV the quark number susceptibility of light quarks and heavy quarks are almost equal in the bottom-up model. This indicates that the heavy quark like charm contribution to thermodynamics of a QCD-like system may start to become significant at temperatures T ∼ 600 MeV. In D3/D7 model, we focus on the competition between the quark chemical potential, which enhances the quark number susceptibility, and the quark mass that suppresses the susceptibility. We observe that depending on the relative values of the quark mass and the quark chemical potential, the quark number susceptibility shows a diverging or converging behavior. We also calculate the chiral susceptibility in D3/D7 model to support the observation made with the quark number susceptibility.
Progress in Particle and Nuclear Physics, 2013
At the dawn of a new theoretical tool based on the AdS/CFT correspondence for nonperturbative asp... more At the dawn of a new theoretical tool based on the AdS/CFT correspondence for nonperturbative aspects of quantum chromodynamics, we give an interim review on the new tool, holographic QCD, with some of its accomplishment. We try to give an A-to-Z picture of the holographic QCD, from string theory to a few selected top-down holographic QCD models with one or two physical applications in each model. We may not attempt to collect diverse results from various holographic QCD model studies.
Physical Review D, 2007
In the framework of a holographic QCD approach we study an influence of matters on the deconfinem... more In the framework of a holographic QCD approach we study an influence of matters on the deconfinement temperature, T c. We first consider quark flavor number (N f) dependence of T c. We observe that T c decreases with N f , which is consistent with a lattice QCD result. We also delve into how the quark number density ρ q affects the value of T c. We find that T c drops with increasing ρ q. In both cases, we confirm that the contributions from quarks are suppressed by 1/N c , as it should be, compared to the ones from a gravitational action (pure Yang-Mills).
Physical Review D, 2008
We study the physics with finite nuclear density in the framework of AdS/QCD with holographic bar... more We study the physics with finite nuclear density in the framework of AdS/QCD with holographic baryon field included. Based on a mean field type approach, we introduce the nucleon density as a bi-fermion condensate of the lowest mode of the baryon field and calculate the density dependence of the chiral condensate and the nucleon mass. We observe that the chiral condensate as well as the mass of nucleon decrease with increasing nuclear density. We also consider the mass splitting of charged vector mesons in iso-spin asymmetric nuclear matter.
Physical Review D, 2002
We describe in-medium properties of hadrons in dense matter near chiral restoration using a Wilso... more We describe in-medium properties of hadrons in dense matter near chiral restoration using a Wilsonian matching to QCD of an effective field theory with hidden local symmetry at the chiral cutoff Λ. We find that chiral symmetry is restored in vector manifestationà la Harada and Yamawaki at a critical matter density nc. We express the critical density in terms of QCD correlators in dense matter at the matching scale. In a manner completely analogous to what happens at the critical N c f and at the critical temperature Tc, the vector meson mass is found to vanish (in the chiral limit) at chiral restoration. This result provides a support for Brown-Rho scaling predicted a decade ago. * We reserve µ for chemical potential. † Note that at the level of the bare Lagrangian, there is no vector-axial-vector mixing discussed for hot matter by Dey, Eletsky and Ioffe [16]. At the matching scale, there are no loop corrections. Mixing occurs through hadronic loops when decimation is made. * * The constants κ and λ will also run such that at µ = µc, κ = λ = 1 while at µ < µc, κ = λ. The running will be small near nc, so we will ignore their running here.
Physical Review C, 2000
Based on schematic two-level models extended to a1-meson degrees of freedom, we investigate possi... more Based on schematic two-level models extended to a1-meson degrees of freedom, we investigate possible mechanisms of chiral restoration in the vector/axialvector channels in cold nuclear matter. In the first part of this article we employ the massive Yang-Mills framework to construct an effective chiral Lagrangian based on low-energy mesonic modes at finite density. The latter are identified through nuclear collective excitations of 'meson'-sobar type such as π ↔ [∆(1232)N −1 ] ≡π, ρ ↔ [N * (1520)N −1 ] ≡ρ, etc.. In a mean-field type treatment the in-medium gauge couplingĝ, the (axial-) vector meson masses andfπ are found to decrease with density indicating the approach towards chiral restoration in the language of in-medium effective fields. In the second part of our analysis we evaluate the (first) in-medium Weinberg sum rule which relates vector and axialvector correlators to the pion decay constant. Using in-medium ρ/a1 spectral functions (computed in the two-level model) also leads to a substantial reduction of the pion decay constant with increasing density.
Physical Review C, 2018
We study the phase structure of dense hadronic matter including ∆(1232) as well as N (939) based ... more We study the phase structure of dense hadronic matter including ∆(1232) as well as N (939) based on the parity partner structure, where the baryons have their chiral partners with a certain amount of chiral invariant masses. We show that, in symmetric matter, ∆ enters into matter in the density region of about one to four times of normal nuclear matter density, ρB ∼ 1-4ρ0. The onset density of ∆ matter depends on the chiral invariant mass of ∆, m∆0: The lager m∆0, the bigger the onset density. The ∆ matter of ρB ∼ 1-4ρ0 is unstable due to the existence of ∆, and the stable ∆-nucleon matter is realized at about ρB ∼ 4 ρ0, i.e., the phase transition from nuclear matter to ∆-nucleon matter is of first order for small m∆0, and it is of second order for large m∆0. We find that, associated with the phase transition, the chiral condensate changes very rapidly, i.e., the chiral symmetry restoration is accelerated by ∆ matter. As a result of the accelerations, there appear N * (1535) and ∆(1700), which are the chiral partners to N (939) and ∆(1232), in high density matter, signaling the partial chiral symmetry restoration. Furthermore, we find that complete chiral symmetry restoration itself is delayed by ∆ matter. We also calculate the effective masses, pressure and symmetry energy to study how the transition to ∆ matter affects such physical quantities. We observe that the physical quantities change drastically at the transition density.
Physical Review C, 2015
We construct a model to describe dense hadronic matter at zero and finite temperature, based on t... more We construct a model to describe dense hadronic matter at zero and finite temperature, based on the parity doublet model of DeTar and Kunihiro, with including the iso-singlet scalar meson σ as well as ρ and ω mesons. We show that, by including a six-point interaction of σ meson, the model reasonably reproduces the properties of the normal nuclear matter with the chiral invariant nucleon mass m0 in the range from 500 MeV to 900 MeV. Furthermore, we study the phase diagram based on the model, which shows that the value of the chiral condensate drops at the liquid-gas phase transition point and at the chiral phase transition point. We also study asymmetric nuclear matter and find that the first order phase transition for the liquid-gas phase transition disappears in asymmetric matter and that the critical density for the chiral phase transition at non-zero density becomes smaller for larger asymmetry.
Journal of High Energy Physics, 2009
We investigate the hybrid exotic meson with J P C = 1 −+ within the framework of an AdS/QCD model... more We investigate the hybrid exotic meson with J P C = 1 −+ within the framework of an AdS/QCD model. Introducing a holographic field dual to the operator for hybrid exotic meson, we obtain the eigen-value equation for its mass. Fixing all free parameters by QCD observables such as the ρ-meson mass, we predict the masses of the hybrid exotic meson. The results turn out to be 1476 MeV for the ground state, and 2611 MeV for the first excited one. Being compared with the existing experimental data for the π 1 (1400), which is known to be m π 1 = 1351 ± 30 MeV, the present result seems to be qualitative in agreement with it. We also predict the decay constant of π 1 (1400): F π 1 = 10.6 MeV.
We study strange and isospin asymmetric matter in a bottom-up AdS/QCD model. We first consider is... more We study strange and isospin asymmetric matter in a bottom-up AdS/QCD model. We first consider isospin matter, which has served as a good testing ground for nonperturbative QCD, to discuss if the model is suitable to describe QCD with various chemical potentials. We calculate the µ I-dependencies of the masses and decay constants of the pion and the vector-meson. We discuss a possibility of the charged pion condensation in the matter within the bottom-up AdS/QCD model. Then we investigate strange matter in the model. We calculate the deconfinement temperature in strange and isospin asymmetric matter. One of the interesting results of our study is that the critical temperature at a fixed baryon number density increases when strangeness chemical potential is introduced. This suggests that if matter undergoes a transition to strange matter, the critical temperature shows a sudden jump at the transition point.
We study a meson mass splitting due to isospin violation in holographic dense matter. We work in ... more We study a meson mass splitting due to isospin violation in holographic dense matter. We work in a D4/D6/D6 model with two quark flavor branes to consider asymmetric dense matter in holographic QCD. We mainly consider two cases. We first consider m+/m−simmd/mum^+/m^-\sim m_d/m_um+/m−simmd/mu to study the effect of isospin violation on the meson masses. Then, we take m+/m−simms/mqm^+/m^-\sim m_s/m_qm+/m−simms/mq, where mqsim(mu+md)/2m_q\sim(m_u+m_d)/2mqsim(mu+md)/2, to calculate in-medium kaon-like meson masses. In both cases we observe that the mass splitting of charged mesons occurs at low densities due to the asymmetry, while at high densities their masses become degenerate. At intermediate densities, we find an exotic behavior in masses which could be partly understood in a simple picture based on the Pauli exclusion principle.
Journal of the Korean Physical Society, 2015
We study the effects of flavor symmetry breaking on holographic dense matter and compact stars in... more We study the effects of flavor symmetry breaking on holographic dense matter and compact stars in the D4/D6 model. To this end, two light flavors and one intermediate mass flavor are considered. For two light quarks, we investigate how the strong isospin violation affects the properties of holographic dense matter and compact stars. We observe that quark-antiquark condensates are flavor dependent and show interesting behavior near the transition from dense matter with only one flavor to matter with two flavors. An intermediate mass quark is introduced to investigate the role of the third flavor. The mass-radius relations of holographic compact stars with three flavors show that the mass-radius curve changes drastically at a transition density from which the third flavor begins to appear in the matter.
Journal of High Energy Physics, 2011
We solve the Tolman-Oppenheimer-Volkoff equation using an equation of state (EoS) calculated in h... more We solve the Tolman-Oppenheimer-Volkoff equation using an equation of state (EoS) calculated in holographic QCD. The aim is to use compact astrophysical objects like neutron stars as an indicator to test holographic equations of state. We first try an EoS from a dense D4/D8/D8 model. In this case, however, we could not find a stable compact star, a star satisfying pressure-zero condition with a radius R, p(R) = 0, within a reasonable value of the radius. This means that the EoS from the D4/D8/D8 model may not support any stable compact stars or may support one whose radius is very large. This might be due to a deficit of attractive force from a scalar field or two-pion exchange in the D4/D8/D8 model. Then, we consider D4/D6 type models with different number of quark flavors, N f = 1, 2, 3. Though the mass and radius of a holographic star is larger than those of normal neutron stars, the D4/D6 type EoS renders a stable compact star.
EPJ Web of Conferences, 2012
We study asymmetric dense matter in holographic QCD. We construct asymmetric dense matter by cons... more We study asymmetric dense matter in holographic QCD. We construct asymmetric dense matter by considering two quark flavor branes with different quark masses in a D4/D6/D6 model. To calculate the symmetry energy in nuclear matter, we consider two quarks with equal masses and observe that the symmetry energy increases with the total charge showing the stiff dependence. This behavior is universal in the sense that the result is independent of parameters in the model. We also study strange (or hyperon) matter with one light and one intermediate mass quarks. In addition to the vacuum properties of asymmetric matter, we calculate meson masses in asymmetric dense matter and discuss our results in the light of in-medium kaon masses.
Journal of High Energy Physics, 2008
We study the quark number susceptibility, an indicator of QCD phase transition, in the hard wall ... more We study the quark number susceptibility, an indicator of QCD phase transition, in the hard wall and soft wall models of hQCD. We find that the susceptibilities in both models are the same, jumping up at the deconfinement phase transition temperature. We also find that the diffusion constant in the soft wall model is enhanced compared to the one in the hard wall model.
Hadron and Nuclear Physics 09, 2010
We present in this talk a recent investigation on a unified approach within the framework of a ha... more We present in this talk a recent investigation on a unified approach within the framework of a hard-wall model of AdS/QCD. We first study a theoretical inconsistency in existing models. In order to remove this inconsistency, we propose a unified approach in which the mesons and the nucleons are treated on the same footing, the same infrared (IR) cutoff being employed in both fermionic and bosonic sectors. We also suggest a possible way of improving the model by introducing a five-dimensional anomalous dimension.
Journal of High Energy Physics, 2008
We investigate the quark-gluon mixed condensate based on an AdS/QCD model. Introducing a holograp... more We investigate the quark-gluon mixed condensate based on an AdS/QCD model. Introducing a holographic field dual to the operator for the quark-gluon mixed condensate, we obtain the corresponding classical equation of motion. Taking the mixed condensate as an additional free parameter, we show that the present scheme reproduces very well experimental data. A fixed value of the mixed condensate is in good agreement with that of the QCD sum rules.
Journal of High Energy Physics, 2009
We investigate masses and coupling constants of mesons and nucleons within a hard wall model of h... more We investigate masses and coupling constants of mesons and nucleons within a hard wall model of holographic QCD in a unified approach. We first examine an appropriate form of fermionic solutions by restricting the mass coupling for the five dimensional bulk fermions and bosons. We then derive approximated analytic solutions for the nucleons and the corresponding masses in a small mass coupling region. In order to treat meson and nucleon properties on the same footing, we introduce the same infrared (IR) cut in such a way that the meson-nucleon coupling constants, i.e., g πN N and g ρN N are uniquely determined. The first order approximation with respect to a dimensionless expansion parameter, which is valid in the small mass coupling region, explicitly shows difficulties to avoid the IR scale problem of the hard wall model. We discuss possible ways of circumventing these problems.
Journal of High Energy Physics, 2010
We study the quark number susceptibility in holographic QCD with a finite chemical potential or u... more We study the quark number susceptibility in holographic QCD with a finite chemical potential or under an external magnetic field at finite temperature. We first consider the quark number susceptibility with the chemical potential. We observe that approaching T c from high temperature regime, χ q /T 2 develops a peak as we increase the chemical potential, which confirms recent lattice QCD results. We discuss this behavior in connection with the existence of the critical end point in the QCD phase diagram. We also consider the quark number susceptibility under the external magnetic field. We predict that the quark number susceptibility exhibits a blow-up behavior at low temperature as we raise the value of the magnetic field. We finally spell out some limitations of our study.
Journal of High Energy Physics, 2010
We construct a simple holographic QCD model to study nuclear matter to strange matter transition.... more We construct a simple holographic QCD model to study nuclear matter to strange matter transition. The interaction of dense medium and hadrons is taken care of by imposing the force balancing condition for stable D4/D6/D6 configuration. By considering the intermediate and light flavor branes interacting with baryon vertex homogeneously distributed along R 3 space and requesting the energy minimization, we find that there is a well defined transition density as a function of current quark mass. We also find that as density goes up very high, intermediate (or heavy) and light quarks populate equally as expected from the Pauli principle. In this sense, the effect of the Pauli principle is realized as dynamics of D-branes.
Progress of Theoretical Physics, 2011
We study the effect of a finite quark mass on the quark number susceptibility in the framework of... more We study the effect of a finite quark mass on the quark number susceptibility in the framework of holographic QCD. We work in a bottom-up model with a deformed AdS black hole and D3/D7 model to calculate the quark number susceptibility at finite temperature with/without a finite quark chemical potential. As expected the finite quark mass suppresses the quark number susceptibility. We find that at high temperatures T ≥ 600 MeV the quark number susceptibility of light quarks and heavy quarks are almost equal in the bottom-up model. This indicates that the heavy quark like charm contribution to thermodynamics of a QCD-like system may start to become significant at temperatures T ∼ 600 MeV. In D3/D7 model, we focus on the competition between the quark chemical potential, which enhances the quark number susceptibility, and the quark mass that suppresses the susceptibility. We observe that depending on the relative values of the quark mass and the quark chemical potential, the quark number susceptibility shows a diverging or converging behavior. We also calculate the chiral susceptibility in D3/D7 model to support the observation made with the quark number susceptibility.
Progress in Particle and Nuclear Physics, 2013
At the dawn of a new theoretical tool based on the AdS/CFT correspondence for nonperturbative asp... more At the dawn of a new theoretical tool based on the AdS/CFT correspondence for nonperturbative aspects of quantum chromodynamics, we give an interim review on the new tool, holographic QCD, with some of its accomplishment. We try to give an A-to-Z picture of the holographic QCD, from string theory to a few selected top-down holographic QCD models with one or two physical applications in each model. We may not attempt to collect diverse results from various holographic QCD model studies.
Physical Review D, 2007
In the framework of a holographic QCD approach we study an influence of matters on the deconfinem... more In the framework of a holographic QCD approach we study an influence of matters on the deconfinement temperature, T c. We first consider quark flavor number (N f) dependence of T c. We observe that T c decreases with N f , which is consistent with a lattice QCD result. We also delve into how the quark number density ρ q affects the value of T c. We find that T c drops with increasing ρ q. In both cases, we confirm that the contributions from quarks are suppressed by 1/N c , as it should be, compared to the ones from a gravitational action (pure Yang-Mills).
Physical Review D, 2008
We study the physics with finite nuclear density in the framework of AdS/QCD with holographic bar... more We study the physics with finite nuclear density in the framework of AdS/QCD with holographic baryon field included. Based on a mean field type approach, we introduce the nucleon density as a bi-fermion condensate of the lowest mode of the baryon field and calculate the density dependence of the chiral condensate and the nucleon mass. We observe that the chiral condensate as well as the mass of nucleon decrease with increasing nuclear density. We also consider the mass splitting of charged vector mesons in iso-spin asymmetric nuclear matter.
Physical Review D, 2002
We describe in-medium properties of hadrons in dense matter near chiral restoration using a Wilso... more We describe in-medium properties of hadrons in dense matter near chiral restoration using a Wilsonian matching to QCD of an effective field theory with hidden local symmetry at the chiral cutoff Λ. We find that chiral symmetry is restored in vector manifestationà la Harada and Yamawaki at a critical matter density nc. We express the critical density in terms of QCD correlators in dense matter at the matching scale. In a manner completely analogous to what happens at the critical N c f and at the critical temperature Tc, the vector meson mass is found to vanish (in the chiral limit) at chiral restoration. This result provides a support for Brown-Rho scaling predicted a decade ago. * We reserve µ for chemical potential. † Note that at the level of the bare Lagrangian, there is no vector-axial-vector mixing discussed for hot matter by Dey, Eletsky and Ioffe [16]. At the matching scale, there are no loop corrections. Mixing occurs through hadronic loops when decimation is made. * * The constants κ and λ will also run such that at µ = µc, κ = λ = 1 while at µ < µc, κ = λ. The running will be small near nc, so we will ignore their running here.
Physical Review C, 2000
Based on schematic two-level models extended to a1-meson degrees of freedom, we investigate possi... more Based on schematic two-level models extended to a1-meson degrees of freedom, we investigate possible mechanisms of chiral restoration in the vector/axialvector channels in cold nuclear matter. In the first part of this article we employ the massive Yang-Mills framework to construct an effective chiral Lagrangian based on low-energy mesonic modes at finite density. The latter are identified through nuclear collective excitations of 'meson'-sobar type such as π ↔ [∆(1232)N −1 ] ≡π, ρ ↔ [N * (1520)N −1 ] ≡ρ, etc.. In a mean-field type treatment the in-medium gauge couplingĝ, the (axial-) vector meson masses andfπ are found to decrease with density indicating the approach towards chiral restoration in the language of in-medium effective fields. In the second part of our analysis we evaluate the (first) in-medium Weinberg sum rule which relates vector and axialvector correlators to the pion decay constant. Using in-medium ρ/a1 spectral functions (computed in the two-level model) also leads to a substantial reduction of the pion decay constant with increasing density.