arXiv subjects

Chang Ho Hyun

Publications and source records attributed to Chang Ho Hyun.

At least 37 records · Page 2Linked to original sources

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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arXiv2022

Quasielastic Charged-Current Neutrino-Nucleus Scattering with Nonrelativistic Nuclear Energy Density Functionals

Charged-current neutrino-nucleus scattering is studied in the quasielastic region with the KIDS (Korea-IBS-Daegu-SKKU) nuclear energy density functional. We focus on the uncertainties stemming from the axial mass and the in-medium effective mass of the nucleon. Comparing the result of theory to the state-of-the-art data from MiniBooNE, T2K, and MINER$ν$A, we constrain the axial mass and the effective mass that are compatible with the data. We find that the total cross section is insensitive to the effective mass, so the axial mass could be determined independently of the uncertainty in the effective mass. Differential cross sections at different kinematics are, on the other hand, sensitive to the effective mass as well as the axial mass. Within the uncertainty of the axial mass constrained from the total cross section, dependence on the effective mass is examined. As a result we obtain the axial mass and the effective mass that are consistent with the experimental data.

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arXiv2022

Inclusive electron scattering in the quasielastic region with Korea-IBS-Daegu-SKKU density functional

With the framework of KIDS (Korea-IBS-Daegu-SKKU) density functional model, the isoscalar and isovector effective masses of nucleon and the effect of symmetry energy in nuclear medium are investigated in inclusive $(e,e')$ reaction in quasielastic region. The effective masses are varied in the range $(0.7 \sim 1.0)M$ with free nucleon mass $M$, and the symmetry energy is varied within the uncertainty allowed by nuclear data and neutron star observation. The wave functions of nucleons inside target nucleus are generated by solving Hartree-Fock equation with adjusting equation of state, binding energy and radius of various stable nuclei, and effective mass of nucleon in the KIDS model. With the obtained wave functions, we calculate the differential cross section for the inclusive $(e,e')$ reaction and compare the theoretical results with Bates, Saclay, and SLAC experimental data. Our model describes experimental data better at SLAC-type high incident electron energy than those measured from Bates and Saclay. The influence of the effective mass and symmetry energy appears to be precise on the longitudinal cross section.

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arXiv2021

Neutron skin thickness of $^{48}$Ca, $^{132}$Sn and $^{208}$Pb with KIDS density functional

Neutron skin thickness ($R_{np}$) of the atomic nuclei $^{48}$Ca, $^{132}$Sn and $^{208}$Pb are considered in the KIDS (Korea:IBS-Daegu-Sungkyunkwan) density functional formalism. Model parameters most relevant to $R_{np}$ are constrained from standard nuclear data and neutron star properties determined from modern observations. Mean values of $R_{np}$ are obtained as 0.161, 0.220 and 0.160 fm for $^{48}$Ca, $^{132}$Sn and $^{208}$Pb, respectively, and the corresponding standard deviations are 0.011, 0.020 and 0.021 fm. Correlations between $R_{np}$ of the three nuclei are considered, and we find that $R_{np}$'s are correlated very strongly. We obtain correlation coefficient 0.978 between $R_{np}$ of $^{48}$Ca and $^{208}$Pb, and 0.996 between $R_{np}$ of $^{132}$Sn and $^{208}$Pb.

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arXiv2021

Constraints on the curvature of nuclear symmetry energy from recent astronomical data within the KIDS framework

We investigate the density dependence of the nuclear symmetry energy $S(ρ) $ in the KIDS (Korea-IBS-Daegu-SKKU) framework for the nuclear equation of state (EoS) and energy-density functional (EDF). The aim is to constrain the value of the curvature parameter ($K_{\rm sym}$) based on recent astronomical data. First, assuming a standard saturation point, we calculate bulk nuclear properties within KIDS-EDF for different values of the compression modulus of symmetric nuclear matter ($K_0$) and of the leading-order symmetry energy parameters, i.e., the symmetry energy ($J$) and slope ($L$) at saturation density, each within a broadly accepted range, as well as $K_{\rm sym}$. All of the above EoS parameters are varied independently of each other. The skewness parameter ($Q_{\rm sym}$) is presently kept fixed at 650 MeV. For all EoS parameter sets which describe the selected nuclear data within better than $0.3\%$, we calculate the neutron-star equation of state and mass-radius relation and analyze the results in terms of Pearson correlation coefficients $r$. We find that the value of $K_{\rm sym}$ is strongly correlated with the radius of both a canonical and a massive star ($|r|>0.9$). If we impose that all known astronomical constraints on the neutron star radii must be satisfied, we deduce $-150 < K_{\rm sym}<0$. As a result, the symmetry energy as a function of the density is consistently found to have an inflection point at $ρ_0<ρ<2ρ_0$. We take the opportunity to report that the neutron skin thickness of $^{208}$Pb shows no correlation at all with the neutron star radii ($|r|<0.1$), in contrast with studies which focus on the role of $L$ only.

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arXiv2021

Quasi-elastic electron scattering with KIDS nuclear energy density functional

Isoscalar and isovector effective masses of the nucleon in nuclear medium are explored in the quasi-elastic electron scattering of nuclei with KIDS (Korea-IBS-Daegu-SKKU) density functional model. Effective masses are varied in the range (0.7 ~ 1.0)$M$ where $M$ is the mass of the nucleon in free space. Parameters in the KIDS functional are adjusted to nuclear matter equation of state, energy and radius of selected nuclei, and effective mass of nucleons. Hartree-Fock equation is solved to obtain the wave functions of the nucleon in target nuclei, and they are plugged in the calculation of electron-nucleus scattering cross sections at the energies of incident electrons 300 MeV ~ 2.5 GeV. Theoretical prediction agrees well with measurement. Dependence on the effective mass is evident: cross section tends to increase with small isoscalar effective masses. However, effect of isovector effective mass is negligible. Spectroscopic factors are estimated for the protons in the outermost shells of $^{16}$O, $^{40}$Ca, and $^{208}$Pb. Results are consistent with the values in the literature.

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arXiv2021

Constraining the density dependence of the symmetry energy with nuclear data and astronomical observations in the KIDS framework

The KIDS framework for the nuclear equation of state (EoS) and energy density functional (EDF) offers the possibility to explore symmetry-energy (SE) parameters such as J (value at saturation density), L (slope), Ksym (curvature) and so on independently of each other and of assumptions about the effective mass. Here we examine the performance of EoSs with different SE parameters in reproducing nuclear properties and astronomical observations in an effort to constrain especially L and Ksym or the droplet-model counterpart Ktau. Assuming a standard EoS for symmetric matter, we explore several points on the hyperplane of (J,L,Ksym or Ktau) values. For each point, the corresponding EDF parameters and a pairing parameter are obtained for applications in spherical even-even nuclei. This is the first application of KIDS EDFs with pairing correlations. The EoSs are tested successively on properties of closed-shell nuclei, along the Sn isotopic chain, and on astronomical observations, in a step-by-step process of elimination and correction. A small regime of best-performing parameters is determined. The results strongly suggest that Ksym is negative and no lower than -200MeV, that Ktau lies between roughly -400 and -300MeV and that L lies between 40 and 65MeV with L<55MeV more likely. Correlations between symmetry-energy parameters are critically discussed. Predictions for the position of the neutron drip line and the neutron skin thickness of selected nuclei are reported. They are only weakly affected by the choice of effective mass values. Parts of the drip line can be sensitive to the SE parameters. The results underscore the role of Ktau and of precise astronomical input. Better constraints are possible with precise fits to nuclear energies and, in the future, more-precise input from astronomy.

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arXiv2021

KIDS density functional for deformed nuclei: Examples of the even-even Nd isotopes

Background: A global description of the ground-state properties of nuclei in a wide mass range in a unified manner is desirable not only for understanding exotic nuclei but for providing nuclear data for applications. Purpose: We demonstrate the KIDS functional describes the ground states appropriately with respect to the existing data and predictions for a possible application of the functional to all the nuclei by taking Nd isotopes as examples. Method: The Kohn-Sham-Bogoliubov equation is solved for the Nd isotopes with the neutron numbers ranging from 60 to 160 by employing the KIDS functionals constructed to satisfy both neutron-matter equation of state or neutron star observation and selected nuclear data. Results: Considering the nuclear deformation improves the description of the binding energies and radii. We find that the discrepancy from the experimental data is more significant for neutron-rich/deficient isotopes and this can be made isotope independent by changing the slope parameter of the symmetry energy. Conclusions: The KIDS functional is applied to the mid-shell nuclei for the first time. The onset and evolution of deformation are nicely described for the Nd isotopes. The KIDS functional is competent to a global fitting for a better description of nuclear properties in the nuclear chart.

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arXiv2020

Compression modulus and symmetry energy of nuclear matter with KIDS density functional

Equation of state of dense nuclear matter is explored in the KIDS density functional theory. Parameters of the equation of state which are coefficients of the energy density expanded in powers of $(ρ- ρ_0)/3ρ_0$ where $ρ$ is the nuclear matter density and $ρ_0$ is its density at saturation are constrained by using both nuclear data and the mass-radius relation of the neutron star determined from the modern astronomy. We find that the combination of both data can reduce the uncertainty in the equation of state parameters significantly. We confirm that the newly constrained parameters reproduce the basic properties of spherical magic nuclei with high accuracy. Neutron drip lines, on the other hand, show non-negligible dependence on the uncertainty of the nuclear symmetry energy.

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arXiv2020

Neutron star equation of state and tidal deformability with nuclear energy density functionals

Neutron star is the ultimate testing place for the physics of dense nuclear matter. Before the detection of gravitational waves from the merger of binary neutron stars, various nuclear equations of state have been used to estimate the macroscopic properties of neutron stars, such as masses and radii, based on the electromagnetic observations. However, recent observations on the tidal deformability of neutron star from the gravitational waves GW170817 opened a new era of multi-messenger astronomy and astrophysics, and many theoretical works have been extended to estimate the tidal deformability of neutron stars. In this article, we review our recent works on the application of nuclear energy density functionals to the properties of neutron stars including tidal deformability. We found that many nuclear energy density functionals, including new KIDS (Korea: IBS-Daegu-Sungkyunkwan) model, satisfy both constraints from current electromagnetic and gravitational wave observations. We discuss future possibilities of constraining nuclear matter equation of state from ground-based experiments and multi-messenger observations.

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arXiv2020

Neutrino-Deuteron Reactions at Solar Neutrino Energies in Pionless Effective Field Theory with Dibaryon Fields

We study breakup of the deuteron induced by neutrinos in the neutral $νd\to νnp$, $\barν d\to \barν np$ and the charged $\barν d\to e^+ n n$, $νd\to e^- pp$ processes. Pionless effective field theory with dibaryon fields is used to calculate the total cross sections for neutrino energies $E_ν$ from threshold to 20 MeV. Amplitudes are expanded up to next-to-leading order, and the partial wave is truncated at $P$-waves. The Coulomb interaction between two protons is included nonperturbatively in the reaction amplitudes, and an analytic expression of the amplitudes is obtained. The contribution of the next-to-leading order to the total cross section is in the range of 5.2$-$9.9\% in magnitude, and that of the $P$-wave is 2.4$-$2.8\% at $E_ν= 20$ MeV. Uncertainty arising from an axial isovector low-energy constant is estimated to be on the order of 1\%.

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arXiv2019

From homogeneous matter to finite nuclei: Role of the effective mass

Recent astronomical observations, nuclear-reaction experiments, and microscopic calculations have placed new constraints on the nuclear equation of state (EoS) and revealed that most nuclear structure models fail to satisfy those constraints upon extrapolation to infinite matter. A reverse procedure for imposing EoS constraints on nuclear structure has been elusive. Here we present for the first time a method to generate a microscopic energy density functional (EDF) for nuclei from a given immutable EoS. The method takes advantage of a natural Ansatz for homogeneous nuclear matter, the Kohn-Sham framework, and the Skyrme formalism. We apply it to the realistic nuclear EoS of Akmal-Pandharipande-Ravenhall and describe successfully closed-(sub)shell nuclei. In the process, we provide predictions for the neutron skin thickness of nuclei based directly on the given EoS. Crucially, bulk and static nuclear properties are found practically independent of the assumed effective mass value - a unique result in bridging EDF of finite and homogeneous systems in general.

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arXiv2019

Analysis of nuclear structure in a converging expansion scheme

In the framework of the KIDS generalized energy density functional (EDF), the nuclear equation of state (EoS) is expressed as an expansion in powers of the Fermi momentum or the cubic root of the density ($ρ^{1/3}$). Although an optimal number of converging terms was obtained in specific cases of fits to empirical data and pseudodata, the degree of convergence remains to be examined not only for homogeneous matter but also for finite nuclei. One goal of the present work is to validate the minimal and optimal number of EoS parameters required for the description of homogeneous nuclear matter over a wide range of densities relevant for astrophysical applications. The major goal is to examine the validity of the adopted expansion scheme for an accurate description of finite nuclei. To this end we vary the values of the high-order derivatives of the EoS, namely the skewness of the energy of symmetric nuclear matter and the kurtosis of the symmetry energy, at saturation and examine the relative importance of each term in $ρ^{1/3}$ expansion for homogeneous matter. For given sets of EoS parameters determined in this way, we define equivalent Skyrme-type functionals and examine the convergence in the description of finite nuclei focusing on the masses and charge radii of closed-shell nuclei. The EoS of symmetric nuclear matter is found to be efficiently parameterized with only 3 parameters and the symmetry energy (or the energy of pure neutron matter) with 4 parameters when the EoS is expanded in the power series of the Fermi momentum. Higher-order EoS parameters do not produce any improvement, in practice, in the description of nuclear ground-state energies and charge radii, which means that they cannot be constrained by bulk properties of nuclei.

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arXiv2018

Tidal Deformability of Neutron Stars with Realistic Nuclear Energy Density Functionals

We investigate the constraints on the mass and radius of neutron stars by considering the tidal deformability in the merge of neutron star binaries. In order to extract the most reliable range of uncertainty from theory, we employ models based upon the Skyrme force and density functional theory and select models that are consistent with empirical data of finite nuclei, measured properties of nuclear matter around the saturation density, and observation of the maximum mass of neutron stars. From the selected models, we calculate the Love number $k_2$, dimensionless tidal deformability $Λ$, and mass-weighted deformability $\tildeΛ$ in the binary system. We find that all the models considered in this work give $\tildeΛ$ less than 800 which is the upper limit obtained from the measurement of GW170817. However, the model dependence of tidal deformability is manifest such that our results on the tidal deformability exhibit critical sensitivity to the size of neutron stars.

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arXiv2017

Density dependence of the nuclear energy-density functional

The explicit density (rho) dependence in the coupling coefficients of the non-relativistic nuclear energy-density functional (EDF) encodes effects of three-nucleon forces and dynamical correlations. The necessity for a coupling coefficient in the form of a small fractional power of rho is empirical and the power often chosen arbitrarily. Consequently, precision-oriented parameterisations risk overfitting and loss of predictive power. Observing that the Fermi momentum kF~rho^1/3 is a key variable in Fermi systems, we examine if a power hierarchy in kF can be inferred from the properties of homogeneous matter in a domain of densities which is relevant for nuclear structure and neutron stars. For later applications we want to determine an EDF that is of good quality but not overtrained. We fit polynomial and other functions of rho^1/3 to existing microscopic calculations of the energy of symmetric and pure neutron matter and analyze the fits. We select a form and parameter set which we found robust and examine the parameters' naturalness and the resulting extrapolations. A statistical analysis confirms that low-order terms like rho^1/3 and rho^2/3 are the most relevant ones. It also hints at a different power hierarchy for symmetric vs. pure neutron matter, supporting the need for more than one rho^a terms in non-relativistic EDFs. The EDF we propose accommodates adopted properties of nuclear matter near saturation. Importantly, its extrapolation to dilute or asymmetric matter reproduces a range of existing microscopic results, to which it has not been fitted. It also predicts neutron-star properties consistent with observations. The coefficients display naturalness. Once determined for homogeneous matter, EDFs of the present form can be mapped onto Skyrme-type ones for use in nuclei. The statistical analysis can be extended to higher orders and for different ab initio calculations.

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arXiv2017

Spin polarization observables of the deuteron photodisintegration at low energies in pionless effective field theory

Spin polarization observables of the deuteron photodisintegration at low energies are studied in a pionless effective field theory up to next-to-next-to-leading order (NNLO). The total and differential cross sections, induced neutron polarization $P_{y'}$, and tensor analyzing powers $T_{20}$ and $T_{22}$ of the process are calculated at photon energies from the breakup threshold to 20~MeV. We find that the NNLO corrections in the cross sections and $P_{y'}$ converge well whereas they turn out to be important contributions in $T_{20}$ and $T_{22}$. We discuss the discrepancy between theory and experiment in $P_{y'}$ still persisting as well as an implication of our result to the first measurement of $T_{20}$ at low energies in the HIGS facility.

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arXiv2017

Nuclear Energy Density Functional for KIDS

The density functional theory (DFT) is based on the existence and uniqueness of a universal functional $E[ρ]$, which determines the dependence of the total energy on single-particle density distributions. However, DFT says nothing about the form of the functional. Our strategy is to first look at what we know, from independent considerations, about the analytical density dependence of the energy of nuclear matter and then, for practical applications, to obtain an appropriate density-dependent effective interaction by reverse engineering. In a previous work on homogeneous matter, we identified the most essential terms to include in our "KIDS" functional, named after the early-stage participating institutes. We now present first results for finite nuclei, namely the energies and radii of $^{16,28}$O, $^{40,60}$Ca.

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arXiv2017

Nuclear Equation of State and Neutron Star Cooling

We investigate the cooling of neutron stars with relativistic and non-relativistic models of dense nuclear matter. We focus on the effects of uncertainties originated from the nuclear models, the composition of elements in the envelope region, and the formation of superfluidity in the core and the crust of neutron stars. Discovery of $2 M_\odot$ neutron stars PSR J1614-2230 and PSR J0343+0432 has triggered the revival of stiff nuclear equation of state at high densities. In the mean time, observation of a neutron star in Cassiopeia A for more than 10 years has provided us with very accurate data for the thermal evolution of neutron stars. Both mass and temperature of neutron stars depend critically on the equation of state of nuclear matter, so we first search for nuclear models that satisfy the constraints from mass and temperature simultaneously within a reasonable range. With selected models, we explore the effects of element composition in the evenlope region, and the existence of superfluidity in the core and the crust of neutron stars. Due to uncertainty in the composition of particles in the envelope region we obtain a range of cooling curves that can cover substantial region of observation data.

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