arXiv subjects

Chang Ho Hyun

Publications and source records attributed to Chang Ho Hyun.

At least 19 recordsLinked to original sources

arXiv2026

Structure of multi-$Λ$ hypernuclei with a Skyrme-type $ΛΛ$ interaction constrained by data on double-$Λ$ hypernuclei and neutron stars

We investigate multi-$Λ$ hypernuclear systems with Skyrme-type $ΛΛ$ interactions constrained by the data on double-$Λ$ hypernuclei and neutron stars. The roles of the repulsive $p$-wave and density-dependent terms in the $ΛΛ$ interaction are examined by considering the homogeneous hyperonic matter around the normal density and finite multi-$Λ$ hypernuclei within the spherical Hartree-Fock approach. In homogeneous matter, the $Λ$ chemical potential and corresponding $Λ$ drip point depend strongly on the repulsive $p$-wave term, while the effect of density-dependent term is relatively weak in the density range relevant to finite nuclei. In the multi-$Λ$ hypernuclei built on doubly closed stable cores from light to heavy systems, $Λ$ radius, separation energy and single-particle structure show a clear dependence on the repulsive $p$-wave interaction, and this dependence becomes stronger as the number of $Λ$ hyperons increases. A second and distinct effect appears near the $Λ$ drip line: when the last occupied $Λ$ orbit approaches the continuum, the repulsive $p$-wave term shifts the state upward and can produce a weakly bound state with an extended radial distribution. As a result, $Λ$ radius can increase rapidly near the threshold. This threshold effect should be distinguished from the moderate enhancement of the dependence on $p$-wave interaction with increasing number of $Λ$ hyperons. These results indicate that the multi-$Λ$ hypernuclei are particularly useful for isolating the role of $p$-wave $ΛΛ$ interacion around the normal density, whereas the density-dependent term is expected to be more important interaction in the high-density domain relevant to neutron stars.

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arXiv2026

Bayesian analysis of density profile of light dark matter elucidating the properties of dark matter admixed neutron stars in the presence of hyperons

We study the impact of symmetry energy ($S$), hyperons, and dark matter (DM) on structural and oscillatory properties of neutron stars (NSs). Uncertainty from hadronic equation of state for NSs is considered with 15 relativistic mean field models having slope parameter ($L_0$) of $S$ in range $40-120$ MeV. DM admixed NSs (DMANSs) are described with feeble interaction between light DM fermions ($χ$) with hadronic matter in the presence of hyperons via scalar ($η$) and vector ($ξ$) dark mediators. The masses $m_χ$, $m_η$ and $m_ξ$ are related by self-interaction constraints from bullet cluster. DM self-interaction couplings are related to $m_χ$ by relic density constraint. The DM density is taken as an exponential function of baryon density with a free parameter $α$. Uncertainty from DM model is incorporated by exploring the dependence on $m_χ$ and $α$. Several DM search experiments have almost ruled out the existence of massive DM ($\gtrsim$ GeV). Lately, pursuit for sub-GeV DM has attracted significant attention. Therefore, we consider $m_χ<$ 1 GeV and $α\leq$ 0.1 such that the contribution of DM to the total mass of the DMANSs is $<10\%$. Comparing our results with various astrophysical constraints, we find that the HESS J1731-347 and GW170817 data are very important in determining the presence of light DM in NSs in moderate amount, relevant in the range $L_0\lesssim$ 58 MeV. Employing models of DMANSs that satisfy several observational data, we infer with Bayesian analysis, the likely ranges of $m_χ$ and $α$ are almost independent of the underlying hadronic model within 40 MeV $\lesssim$ $L_0$ $<$ 58 MeV. In the absence of DM and with the most probable values of $m_χ$ and $α$ obtained from the Bayesian inference, we calculate the frequencies of non-radial $f$- and $p_1$-modes oscillation of NSs/DMANSs.

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arXiv2026

Analysis of elastic $α$-$^{12}$C scattering with global optimization in the cluster effective field theory

We analyze the elastic $α$-$^{12}$C scattering including the contribution of resonance states below the $p$-$^{15}$N breakup threshold energy. We use the cluster effective field theory in which scattering amplitude is expanded in terms of the effective range expansion parameters for the angular momentum states from $l=0$ to $l=6$. The amplitude contains 37 parameters, which are determined by fitting to 11 392 differential cross section data points of the elastic $α$-$^{12}$C scattering. To optimize the fitting process, we implement the differential evolution (DE) algorithm, which performs a global search over the high-dimensional parameter space and consistently converges to the same minimum $χ^{2}$ value across independent runs, suggesting proximity to the global minimum within the explored domain. In parallel, the Markov chain Monte Carlo (MCMC) method is used to crosscheck the DE results and to estimate the parameter uncertainties. The best fit yields $χ^{2}/N\!\simeq\!6.2$ for the elastic scattering data. Using the determined 37 parameters, we calculate the differential cross sections and the phase shifts of the elastic $α$-$^{12}$C scattering and compare the results with experimental data and those of an $R$-matrix analysis. Our result of the cross section agrees with the experimental data as accurately as an $R$-matrix analysis. The results demonstrate that the cluster effective field theory, combined with global optimization and uncertainty quantification based on DE-MCMC methods, provides a reliable and systematic framework for applications to low energy phenomena relevant to stellar evolution and nucleosynthesis.

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arXiv2026

Constraining the $ΛΛ$ interaction with terrestrial and astronomical data

Terrestrial double-$Λ$ hypernuclear data and astronomical observations of neutron stars provide complementary constraints on the $ΛΛ$ interaction. In this work, we investigate the $ΛΛ$ interaction within a Skyrme energy density functional framework based on the KIDS (Korea-IBS-Daegu-SKKU) models. We employ a Skyrme-type $ΛΛ$ interaction that includes the standard $s$- and $p$-wave terms, as well as a density-dependent term that effectively represents an $NΛΛ$ three-body force. The $s$-wave terms are constrained using data on double-$Λ$ hypernuclei supplemented by pseudodata obtained from core + $2Λ$ three-body model calculations including heavier hypernuclei. We show that the data on heavier systems are essential to simultaneously constrain the two $s$-wave parameters. We further explore the impact of the $p$-wave and $NΛΛ$ components on the neutron-star properties and find that appropriate repulsive contributions of these terms yield consistency with current neutron-star mass-radius observations. These results indicate that the present framework provides phenomenologically acceptable equations of state for dense $(N,Λ)$ matter over a wide range of densities and highlight the importance of future experimental data on heavier double-$Λ$ hypernuclei.

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arXiv2025

$f$ and $p$ mode oscillation of proto-neutron stars with systematic variation of the nucleon effective mass

We develop equation of state (EoS) of proto-neutron stars (PNSs) at various stages of evolution by varying entropy per baryon $S$, using the Korea-IBS-Daegu-SKKU density functional model. With finite values for both temperature and density, we systematically investigate the influence of nucleon effective mass on EoS of PNSs, for different values of isoscalar effective mass $μ_S^*$. For high entropy values, we aim to replicate conditions of failed core-collapse supernovae forming black holes. At each stage of evolution, structural and non-radial oscillation (fundamental $f$-mode and first pressure $p_1$-mode) properties are computed under isentropic conditions by varying $μ_S^*$. We focus on the effects of $S$ and $μ_S^*$ on oscillation frequencies $f_f$ and $f_{p_1}$ adopting complete general relativistic formalism and Cowling approximation. Thermal effects reduce the values of $f_f$ and $f_{p_1}$ of PNSs compared to those of cold NSs, consequently detection of the former gets facilitated. For high-mass PNSs, this reduction is more pronounced for $f_{p_1}$ than $f_f$. Moreover, lower values of $μ_S^*$ reduce $f_f$ and $f_{p_1}$ further. Universality of mass-scaled angular frequency ($ω_fM$) with compactness ($C$) and tidal deformability ($Λ$) are obtained as non-linear fits that shift upwards (downwards) in $ω_fM-C$ ($ω_fM-Λ$) plane for increasing values of $S$. For fixed $S$, the universality is also retained for variation of $μ_S^*$. $S$ shows stronger correlation than $μ_S^*$ with structural and oscillation properties of (P)NSs. Strength of correlation of $S$ is more prominent with $f_{p_1}$ than $f_f$ while the trend is opposite for $μ_S^*$. These findings suggest that detection of oscillation frequencies by upcoming GW detectors, could potentially indicate the evolutionary stage of a star during its transition from supernova to cold NS.

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arXiv2025

Non-radial oscillations of hadronic neutron stars, quark stars, and hybrid stars : Calculation of $f$, $p$, and $g$ mode frequencies

The composition and equation of state (EoS) of dense matter relevant to compact stars are quite inconclusive. However, certain observational constraints on the structural properties of compact stars help us constrain the EoS to a fair extent. Moreover, gravitational asteroseismology gives a notion of the composition and EoS of compact stars. The next generation gravitational wave (GW) detectors are likely to detect several oscillation mode frequencies of the GWs. In this work we compute the fundamental ($f$) and the first pressure ($p_1$) mode frequencies ($f_f$ and $f_{p1}$, respectively) with different compositions viz., hadronic, quark, and hybrid star (HS) matter. For HSs, we also study the gravity ($g$) mode frequency ($f_g$). For each phase we also study the correlation between the oscillation frequencies of 1.4 $M_{\odot}$ and 2.01 $M_{\odot}$ compact stars with other different properties. We find that various possible composition of compact stars substantially affects the oscillation frequencies. However, the mass-scaled angular $f$ mode frequency ($ω_f M$) varies universally with compactness ($C$) for all hadronic, quark and hybrid stars. The $f$ mode frequency ($f_{f_{1.4}}$) of the canonical 1.4 $M_{\odot}$ compact star, obtained with different composition, is quite correlated with the canonical radius ($R_{1.4}$) and tidal deformability ($Λ_{1.4}$) while $f_{p_{1.4}}$ is well correlated with slope parameter of the symmetry energy. We also show that $f_{g_{1.4}}$ of the HSs varies almost linearly with $Λ_{1.4}$. Should $g$ modes be detected, they could not only support the existence of HSs, but $f_g$ could be useful to understand the strength of quark repulsion in HSs.

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arXiv2025

Influence of the effective mass on the properties of nuclear matter at finite density and temperature

Significance of the chiral symmetry restoration is studied by considering the role of the modification of the nucleon mass in nuclear medium at finite density and temperature. Using the Korea-IBS-Daegu-SKKU density functional theory, we can create models that have an identical nuclear matter equation of state but different isoscalar and isovector effective masses at zero temperature. Effect of the effective mass becomes transparent at non-zero temperatures, and it becomes more important as temperature increases. Role of the effective mass is examined thoroughly by calculating the dependence of thermodynamic variables such as free energy, internal energy, entropy, pressure and chemical potential on density, temperature and proton fraction. We find that sensitivity to the isoscalar effective mass is several times larger than that of the isovector effective mass, so the uncertainties arising from the effective mass are dominated by the isoscalar effective mass. In the analysis of the relative uncertainty, we obtain that the maximum uncertainty is less than 2% for free energy, internal energy and chemical potential, but it amounts to 20% for pressure. Entropy shows a behavior completely different from the other four variables that the uncertainty is about 40% at the saturation density and increases monotonically as density increases. Effect of the uncertainty to properties of physical systems is investigated with the proto-neutron star. It is shown that temperature depends strongly on the effective mass at a given density and substantial swelling of the radius occurs due to the finite temperature. Equation of state is stiffer with smaller isoscalar effective mass, so the effect of the effective mass appears clearly in the mass-radius relation of the proto-neutron star, larger radius corresponding to smaller effective mass.

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arXiv2024

Correlation between alpha-decay half-lives and symmetry energy

We study the alpha-decay half-lives of 84 <= Z <= 92 even-even nuclei in the semiclassical WKB approximation framework using the density-dependent cluster model and the density distribution described by various Korea-IBS-Daegu-SKKU (KIDS) models. Main goal of this work is to find a correlation between the alpha-decay half-lives and the stiffness of the symmtery energy. Parameters of KIDS model are determined to reproduce the nuclear data (energy and charge radii of 40Ca, 48Ca and 208Pb) and the neutron star observations including constraints by NICER, tidal deformability from GW170817, and the maximum mass limit of neutron star observations. We use the KIDS models (A-D) which have distinctive values for the parameters controlling the stiffness of the nuclear matter equation of state. We find that the alpha-decay half-lives increase systematically from KIDS-A model to KIDS-D model. This implies a correlation between the alpha-decay half-lives and the symmetry energy. We find that the correlation can be understood from the dependence of the particle distribution in the core and the surface region on the symmetry energy.

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arXiv2024

Effect of neutrino electromagnetic properties on the quasielastic neutral-current neutrino-nucleus scattering

In the quasielastic region, we investigate the effect of neutrino electromagnetic properties constrained from the recent experiments on the electroweak neutral current reaction process of the neutrino-$^{12}$C scattering. For a relativistic description of the nuclear dynamics, we employ the relativistic mean-field model, which has been proven to describe the data nicely in the quasielastic region. In the present work, we analyze the influence beyond the Standard Model by considering the neutrino magnetic and electric dipole form factors and charge radius on the neutrino electroweak interactions within $^{12}$C. To this end, we use the values of the neutrino charge radius and the magnetic moment at the squared four momentum transfer $Q^2=0$ obtained from the recent experiments and calculate the neutrino differential cross section of the neutrino-$^{12}$C scattering. We find that the effect of the charge radius and the electric dipole form factor is very small, but the role of the magnetic dipole form factor is sensitive to $Q^2$ and becomes sizable at small momentum transfer.

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arXiv2024

Hadron-quark phase transition in the neutron star with vector MIT bag model and Korea-IBS-Daegu-SKKU functional

Employing the Korea-IBS-Daegu-SKKU (KIDS) density functional for the hadron phase and the MIT bag model with vector (vBag) model for the quark phase, we obtain hadron-quark phase transition in neutron stars considering Maxwell construction. The structural properties of the resultant hybrid stars are computed for three different values of bag constant ($B$) in the range $B^{1/4}=$(145$-$160 MeV). We study the effects of symmetry energy ($J$) on the hybrid star properties with the different KIDS model and found that $J$ has important influence not only on the transition properties like the transition mass, transition radius and jump in density due to phase transition, but also on the stability of the hybrid stars. The vector repulsion of the quark phase via the parameter $G_V$ has profound influence in obtaining reasonable hybrid star configurations, consistent with the recent astrophysical constraints on the structural properties of compact stars. Within the aforesaid range of $B$, the value of $G_V$ is constrained to be 0.3 $\lesssim G_V \lesssim$ 0.4 in order to obtain reasonable hybrid star configurations.

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arXiv2024

Folding potential with modern nuclear density functionals and application to 16O+208Pb reaction

Double folding potential is constructed using the M3Y interaction and the matter densities of the projectile and target nuclei obtained from four microscopic energy density functional (EDF) models. The elastic scattering cross sections for the 16O+208Pb system are calculated using the optical model with the double folding potentials of the four EDF models. We focus on the correlation between the matter densities and the behavior the double folding potential and the elastic scattering cross sections. First, the matter and charge densities are examined by comparing the results of the four EDF models. There is a slight difference in the density in the internal region, but it is negligible in the outer region. Next, we calculate the double folding potential with the matter densities obtained from the four EDF models. Differences between the models are negligible in the outer region, but the potential depth in the internal region shows model dependence, which can be understood from the behavior of matter densities in the internal region. Another point is that the double folding potential is shown to be weakly dependent on the incident energy. Finally, the elastic scattering cross sections have no significant model dependence except for the slight difference in the backward angle.

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arXiv2023

$ΛΛ$ Interaction in a Nuclear Density Functional Theory and Hyperon Puzzle of the Neutron Star

A Skyrme-type effective potential is determined to describe the interaction between $Λ$ hyperons in nuclear medium. Experimental data of the binding energies of the double-$Λ$ ($ΛΛ$) nuclei with mass numbers $A=10$--$13$ are used to fit the parameters of the $ΛΛ$ interaction. As a result of the fitting, we obtain eight different sets of the $ΛΛ$ interaction parameters, which reproduces the input data within 5\% deviation from the experimental data on average. The eight $ΛΛ$ interactions are plugged in the calculation of the heavier $ΛΛ$ nuclei and the neutron star equation of state to explore the issue of hyperon puzzle. We found that the $ΛΛ$ interaction, specifically, p-wave interaction makes the equation of state stiff enough that the maximum mass of the neutron star can be as large as, or above $2\;M_\odot$.

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arXiv2023

Effects of Symmetry Energy on the Equation of State for Hybrid Neutron Stars

In this paper, the implications of the symmetry energy on the hadron and quark phase transitions in the compact star, including the properties of the possible configurations of the quark-hadron hybrid stars, are investigated in the frameworks of the energy-density functional (EDF) models and the flavor SU(2) Nambu--Jona-Lasinio (NJL) model with the help of the Schwinger's covariant proper-time regularization (PTR) scheme. In this {theoretical setup}, the equations of states (EoSs) of hadronic matter for various values of symmetry energies obtained from the EDF models are employed to describe the hadronic matter, and the {flavor} SU(2) NJL model with various repulsive-vector interaction strengths are used to describe the quark matter. We then observe the obtained EoS in the mass-radius properties of the hybrid star configurations for various vector interactions and nuclear symmetry energies by solving the Tolman-Oppenheimer-Volkoff equation. We obtain that the critical density at which the phase transition occurs varies over the density (3.6--6.7)$ρ_0$ depending on the symmetry energy and the strength of the vector coupling $G_v$. The maximum mass of the neutron star (NS) is susceptible to $G_v$. When there is no repulsive force, the NS maximum mass is only about $1.5M_\odot$, but it becomes larger than $2.0M_\odot$ when the vector coupling constant is about half of the {attractive} scalar coupling constant. Surprisingly, the presence of the quark matter does not affect the canonical mass of NS ($1.4M_\odot$), so observing the canonical mass of NSs can provide unique constraints to the EoS of hadronic matter at high densities.

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arXiv2023

Neutrino propagation in the neutron star with uncertainties from nuclear, hadron, and particle physics

In the present work, we investigate the neutral-current neutrino-nucleon scattering in the nuclear medium using various energy-density functional (EDF) models such as the KIDS (Korea-IBS-Daegu-SKKU) and SLy4, together with the quark-meson coupling (QMC) model for the nucleon form factors at finite density. The differential cross section (DCS) and neutrino mean free path (NMFP) are computed numerically, considering the density-dependent nucleon form factors (DDFF) and neutrino structural properties such as the neutrino magnetic moment (NMM) and its electric charge radius (NCR). It turns out that the DDFF decreases the scattering cross-section, while the NCR increases it considerably. The effect of the NMM turns out to be almost negligible. We also observe that the value of the neutron effective mass is of importance in the neutron-star cooling process, indicating that for the neutron effective mass larger than the mass in free space, the neutrino can interact with matter at densities $ρ\gtrsim 1.5 ρ_0$ in the neutron star with radius 13 km.

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arXiv2023

Nuclear mass table in density functional approach inspired by neutron-star observations

Background: Nuclear energy-density functional (EDF) approach has been widely used to describe nuclear-matter equations of state (EoS) and properties of finite nuclei. Recent advancements in neutron-star (NS) observations have put constraints on the nuclear EoS. The Korea-IBS-Daegu-SKKU (KIDS) functional has been then developed to satisfy the NS observations and applied to homogeneous nuclear matter and spherical nuclei. Purpose: We examine the performance of the KIDS functional by calculating the masses and charge radii of even-even nuclei towards the drip lines. Method: The Kohn-Sham-Bogoliubov equation is solved by taking into account the axial deformation. Results: The root-mean-square deviation of the binding energy and the charge radius for the KIDS functional is 4.5--5.1 MeV and 0.03--0.04 fm, which is comparable to that for existing EDFs. The emergence and development of nuclear deformation in open-shell nuclei are well described. The location of the neutron drip line is according to the nuclear-matter parameter characterizing the low-mass NS. Conclusions: The NS-observation-inspired EDF offers a reasonable reproduction of the structures of finite nuclei. A future global optimization including more nuclear data will give better accuracy and high predictive power of neutron-rich nuclei.

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arXiv2022

Neutron skin of $^{27}$Al with Skyrme and Korea-IBS-Daegu-SKKU density functionals

Recent measurement of the parity-violating (PV) asymmetry in the elastic electron scattering on $^{27}$Al target evokes the interest in the distribution of the neutron in the nucleus. In this work, we calculate the neutron skin thickness ($R_{np}$) of $^{27}$Al with nonrelativistic nuclear structure models. We focus on the role of the effective mass, symmetry energy and pairing force. Models are selected to have effective masses in the range $(0.58-1.05)M$ where $M$ is the nucleon mass in free space, and stiffness of the symmetry energy is varied by choosing the slope of the symmetry energy in the range 9.4 -- 100.5 MeV. Effect of pairing force is investigated by calculating $R_{np}$ with and without pairing, and using two different forms of the pairing force. With nine models, we obtain $R_{np} = 0.001 - 0.014$ fm. The result is independent of the effective mass, symmetry energy, and the form of pairing force. However, $R_{np}$ is negative when the pairing force is switched off, so the pairing force plays an essential role to make $R_{np}$ positive and constrained in a narrow range. We also calculate the PV asymmetry ($A_{\rm pv}$) in the elastic electron-$^{27}$Al scattering in the Born approximation at the kinematics of the Qweak experiment. We obtain a very narrow-ranged result $A_{\rm pv} = $ (2.07 -- 2.09) $\times 10^{-6}$. The result is consistent with the experiment and insensitive to the effective mass, symmetry energy and pairing force.

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arXiv2022

Effect of nucleon effective mass and symmetry energy on the neutrino mean free path in a neutron star

The Korea-IBS-Daegu-SKKU energy density functional (KIDS-EDF) models, constructed from the perturbative expansion of the energy density in nuclear matter, have been successfully and widely applied in describing the properties of finite nuclei and infinite nuclear matter. In the present work, we extend the applications of the KIDS-EDF models to investigate the implications of the nucleon effective mass and nuclear symmetry energy for the properties of neutron stars (NSs) and neutrino interaction with the NS constituent matter in the linear response approximation (LRA). At fixed neutrino energy and momentum transfer, we analyze the total differential cross section of neutrino, the neutrino mean free path (NMFP), and the NS mass-radius (M-R) relations. Remarkable results are given by the KIDS0-m*87 and SLy4 models, in which $M_n^* /M \lesssim 1$, and their NMFPs are quite higher in comparison with those obtained from the KIDS0, KIDS-A, and KIDS-B models, which result in $M_n^*/M \gtrsim 1$. For the KIDS0, KIDS-A, and KIDS-B models, we obtain $λ\lesssim R_{\textrm{NS}}$, indicating that these models could predict the slow NS cooling and neutrino trapping in NSs. In contrast, the KIDS0-m*87 and SLy4 models yield $λ\gtrsim R_{\textrm{NS}}$ and thus we expect faster NS cooling and a small possibility of neutrino trapping within NSs. We also calculate the NMFP as a function of the neutrino energy and the nuclear matter density and find that the NMFP decreases as the density and neutrino energy increase, which is consistent with the result obtained in the Brussels-Montreal Skyrme (BSk17 and BSk18) models at saturation density.

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arXiv2022

Effects of Many-body Interactions in Hypernuclei with Korea-IBS-Daegu-SKKU Functionals

We investigate the properties of $Λ$ hyperon in $Λ$-hypernuclei using an effective nuclear density functional theory which is based on the low-energy effective field theory. It expands the energy density in the power of Fermi momentum, and consequently has multiple density dependence for the effective many-body interactions. Starting from the effective density functional for nucleons, we determine the parameters for the two- and many-body $Λ$-$N$ interactions added to the nucleon energy density functional by fitting to $Λ$-hypernuclear data. The experimental data consist of the energy levels of a $Λ$ hyperon in the $p$-, and $d$-states as well as $s$-state of $Λ$-hypernuclei in the mass range from $_Λ^{16}$O to $_Λ^{208}$Pb. The results turn out to properly explain the data relevant to hypernuclei owing to the effective many-body interaction apart from a few data in light hypernuclei. This hyperon functional is applied to study the $Λ$ hyperon binding energy of the neutron-rich $^{124-136}_Λ$Sn isotopes which are under consideration for the measurement at J-PARC. Our results are shown to be insensitive to the density dependence of symmetry energy. We also examine the nuclear matter including $Λ$ hyperon. We note that the hyperon threshold density depends on the nuclear matter properties.

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