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Myung-Ki Cheoun

Publications and source records attributed to Myung-Ki Cheoun.

At least 55 records · Page 3Linked to original sources

Big Bang Nucleosynthesis constraints on the Energy-Momentum Squared Gravity: The $\mathbb{T}^{2}$ model

Scale-independent energy-momentum squared gravity (EMSG) allows different gravitational couplings for different types of sources and has been proven to have interesting implications in cosmology. In this paper, the Big Bang Nucleosynthesis (BBN) formalism and the latest observational constraints on nuclear abundances are being used to put bounds on this class of modified gravity models. Using the tight constraint from BBN on the correction term in the Friedmann equation in EMSG scenario, we report the allowed deviation from the standard cosmic expansion rate.

astro-ph.CO↗

Exploring the Neutrino Mass Hierarchy from Isotopic Ratios of Supernova Nucleosynthesis Products in Presolar Grains

We study the nucleosynthesis in a core-collapse supernova model including newly calculated neutrino-induced reaction rates with both collective and Mikheyev-Smirnov-Wolfenstein (MSW) neutrino-flavor oscillations considered. We show that the measurement of a pair of $^{11}$B/$^{10}$B and $^{138}$La/$^{139}$La or $^6$Li/$^7$Li and $^{138}$La/$^{139}$La in presolar grains that are inferred to have originated from core-collapse supernovae could constrain the neutrino mass hierarchy. The new shell-model and the model of quasi-particle random phase approximation in the estimate of three important neutrino-induced reactions, $ν+^{16}$O, $ν+^{20}$Ne, and $ν+^{138}$Ba are applied in our reaction network. The new rates decrease the calculated $^{7}$Li/$^{6}$Li ratio by a factor of five compared with the previous study. More interestingly, these new rates result in a clear separation of the isotopic ratio of $^{11}$B/$^{10}$B between normal and inverted mass hierarchies in the O/Ne, O/C, and C/He layers where $^{138}$La abundance depends strongly on the mass hierarchy. In these layers, the sensitivity of the calculated abundances of $^{10,11}$B and $^{6,7}$Li to the nuclear reaction uncertainties is also tiny. Therefore, we propose that the $^{11}$B/$^{10}$B vs. $^{138}$La/$^{139}$La and $^6$Li/$^7$Li vs. $^{138}$La/$^{139}$La in type X silicon carbide grains sampled material from C/He layer can be used as a new probe to constrain the neutrino mass hierarchy.

astro-ph.SR↗

Effective Lagrangian for strong and electromagnetic interactions of high-spin resonances

Recent experiments of photon-nucleon and meson-nucleon scatterings have accumulated a lot of data for various meson production processes. One of the purposes of those experiments is to search for the missing resonances which are not discovered until now but whose existence was predicted by hadron models. The analyses of the data requires the development of dynamical coupled-channel models. Since several missing resonances are expected to have spin higher than 3/2, we need to include higher-spin resonances in dynamical coupled-channel models, which enable us to determine the couplings of effective Lagrangians of higher-spin baryons with pseudoscalar mesons or vector mesons. However, hadron models, such as quark models, give predictions only of the decay amplitudes of such baryons. Here we demonstrate the formalism of high-spin resonances and construct the relation between the coupling constants of effective Lagrangians and the partial decay widths that can be predicted by hadron models. This allows us to compare the coupling constants to the hadron model predictions not only in magnitude but in sign as well.

hep-ph↗

Novel features of asymmetric nuclear matter from terrestrial experiments and astrophysical observations of neutron stars

The accurate measurement of neutron skin thickness of $^{208}$Pb by the PREX Collaboration suggests a large value of the nuclear symmetry energy slope parameter, $L$, whereas the smaller $L$ is preferred to account for the small neutron-star radii from NICER observations. To resolve this discrepancy between nuclear experiments and astrophysical observations, new effective interactions have been developed using relativistic mean-field models with the isoscalar- and isovector-meson mixing. We investigate the effects of $δ$-nucleon coupling and $σ$--$δ$ mixing on the ground-state properties of finite nuclei, as well as the characteristics of isospin-asymmetric nuclear matter and neutron stars. Additionally, we explore the role of the quartic $ρ$-meson self-interaction in dense nuclear matter to mitigate the stiff equation of state for neutron stars resulting from the large $δ$-nucleon coupling. It is found that the nuclear symmetry energy undergoes a sudden softening at approximately twice the saturation density of nuclear matter, taking into account the PREX-2 result, the recent NICER observation of PSR J0437$-$4715, and the binary neutron star merger, GW170817.

nucl-th↗

Photon vortex generation from nonlinear Compton scattering in Feynman approach

In the present study, we show calculation of nonlinear Compton scattering with circularly polarized photons in a cylindrical coordinate using Feynman diagram to calculate photon vortex generation in intermediate states considering conservation of angular momentum. We take two different vortex wave functions based on Bessel function for the emitted photon and the electron after emission of the photon, which are the eigenstate of z component of the total angular momentum (zTAM) when a particle propagates along z axis. The result shows that when an electron absorbs N photons a photon vortex with a zTAM = N is predominantly radiated, but there are still very small contributions of photons with a zTAM = (N-1) and (N +1) due to the spin flip of the initial electron. This means even when an electron absorbs only a single photon, the electron may emit a photon vortex of a zTAM of 2 h-bar. However, the numerical calculations show that the contribution of the spin flip is four orders of magnitude smaller than that of the dominant radiation. We also discuss the circular polarization for the generated photon vortices.

hep-ph↗

Nuclear Pairing Energy vs Mean Field Energy: Do They Talk To Each Other For Searching The Energy Minimum?

We study the evolution of the total binding energy (TBE) and pairing energy of Pb, Hg and Ar isotopes, as a function of the nuclear deformation. As for the nuclear model, we exploit a deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc), and a deformed Skyrme Hartree-Fock plus BCS model. It is found that the dependence of pairing energy on the deformation is strongly correlated to that of the mean field energy, which is obtained by subtracting the pairing energy from the TBE; in other words, the energy minimum characterized by a large negative mean field energy has a smaller negative pairing energy or, equivalently, a smaller positive pairing gap, while a stronger pairing energy is found in the region away from the minimum of the total energy. Consequently, the two energies show an anti-symmetric feature in their deformation dependence, although the energy scales are very different. Moreover, since the pairing energy has a negative sign with respect to to the pairing gap, the evolution of mean field energy follows closely that of the pairing gap. This implies that the pairing energy (or pairing gap) and the mean field energy talk to each other and work together along the potential energy curve to determine the energy minimum and/or the local minimum.

nucl-th↗

Effect of isoscalar and isovector scalar fields on baryon semileptonic decays in nuclear matter

The precise determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements is very important, because it could be a clue to new physics beyond Standard Theory. This is particular true of $V_{ud}$, because it is the main contribution to the unitary condition of the CKM matrix elements. The level of accuracy for the test of the unitarity involving the element $V_{ud}$ is now of the order of $10^{-4}$. Because the precise data for $V_{ud}$ is usually extracted from super-allowed nuclear $β$ decay, it is quite significant to investigate the breaking of SU(3) flavor symmetry on the weak vector coupling constant in nuclear matter. The purpose of this paper is to investigate how the isoscalar scalar ($σ$) and the isovector scalar ($δ$ or $a_0$) mean-fields affect the weak vector and axial-vector coupling constants for semileptonic baryon (neutron, $Λ$ or $Ξ^-$) decay in asymmetric nuclear matter. To do so, we use the quark-meson coupling (QMC) model, where nuclear matter consists of nucleons including quark degrees of freedom bound by the self-consistent exchange of scalar and vector mesons. We pay careful attention to the center of mass correction to the quark currents in matter. We then find that, for neutron $β$ decay in asymmetric nuclear matter, the defect of the vector coupling constant due to the $δ$ field can be of the order of $10^{-4}$ at the nuclear saturation density, which is the same amount as the level of the current uncertainty in the measurements. It is also interesting that, in neutron-rich matter, there exists a certain low density at which isospin symmetry is restored, that is, the $u$-$d$ quark mass difference vanishes. We conclude that the effect of the isoscalar scalar and the isovector scalar fields should be considered in baryon semileptonic decays in nuclei.

hep-ph↗

Electromagnetic $|G_E/G_M|$ ratios of hyperons at large timelike $q^2$

In recent years, it has become possible to measure not only the magnitude of the electric ($G_E$) and magnetic ($G_M$) form factors of spin $\frac{1}{2}$ baryons, but also to measure the relative phases of those quantities in the timelike kinematic region. Aiming to interpret present $|G_E/G_M|$ data on hyperons of the baryon octet, as well as to predict future data, we present model calculations of that ratio for large invariant 4-momentum square $q^2$ in the timelike region ($q^2>0$). Without any further parameter fitting,we extend to the timelike region a covariant quark model previously developed to describe the kinematic spacelike region ($q^2 \le 0$) of the baryon octet form factors. The model takes into account both the effects of valence quarks and the excitations of the meson cloud which dresses the baryons. This application to the timelike region assumes an approximation based on unitarity and analyticity that is valid only in the large $q^2$ region. Using the recent data from BESIII we establish the regime of validity of this approximation. We report here that our results for the effective form factor (combination of $|G_E|$ and $|G_M|$) are in good agreement with the data already for $q^2$ values above 15 GeV$^2$. In addition, a more conservative onset of the validity of the approximation is provided by the newly available $|G_E/G_M|$ data which suggest that our predictions may be compared against data for $q^2 \ge $ 20 GeV$^2$. This is expected in the near future, when the range of the present measurements is expanded to the 20--50 GeV$^2$ region.

hep-ph↗

Deciphering Super El Niño: Development of a Novel Predictive Model Integrating Local and Global Climatic Signals

In recent years, extreme weather events have surged, highlighting the urgent need for action on the climate emergency. The year 2023 saw record-breaking global temperatures, unprecedented heatwaves in Europe, devastating floods in Asia, and severe wildfires in North America and Australia. Super El Niño events, known for their profound impact on global weather, play a critical role in these changes, causing severe economic and environmental damage. This study presents a novel predictive model that integrates systematically local and global climatic signals to forecast Super El Niño events, introducing the Super El Niño Index (SEI), which value of 80 or higher defines a Super El Niño event. Our analysis shows that the SEI accurately reflects past Super El Niño events, including those from 1982-83, 1997-98, and 2015-16, with SEI values for these periods containing 80 within the 2-sigma standard deviation. Using data up to 2022, our model predicted an SEI of around 80 for 2023, indicating a Super El Niño for the 2023-24 period. Recent observations confirm that the 2023-24 El Niño is among the five strongest recorded Super El Niño events in history. An analysis of SEI trends from 1982 to 2023 reveals a gradual increase, with recent El Niño events consistently exceeding SEI values of 70. This trend suggests that El Niño events are increasingly approaching Super El Niño intensity, potentially due to more favorable conditions in the equatorial Pacific. This increase in SEI values and the frequency of stronger El Niño events may be attributed to the ongoing effects of global warming. These findings emphasize the need for heightened preparedness and strategic planning to mitigate the impacts of future Super El Niño events, which are likely to become more frequent in the coming decades.

physics.ao-ph↗

Nuclear mass table in deformed relativistic Hartree-Bogoliubov theory in continuum, II: Even-$Z$ nuclei

The mass table in the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional has been established for even-$Z$ nuclei with $8\le Z\le120$, extended from the previous work for even-even nuclei [Zhang $\it{et.~al.}$ (DRHBc Mass Table Collaboration), At. Data Nucl. Data Tables 144, 101488 (2022)]. The calculated binding energies, two-nucleon and one-neutron separation energies, root-mean-square (rms) radii of neutron, proton, matter, and charge distributions, quadrupole deformations, and neutron and proton Fermi surfaces are tabulated and compared with available experimental data. A total of 4829 even-$Z$ nuclei are predicted to be bound, with an rms deviation of 1.477 MeV from the 1244 mass data. Good agreement with the available experimental odd-even mass differences, $α$ decay energies, and charge radii is also achieved. The description accuracy for nuclear masses and nucleon separation energies as well as the prediction for drip lines is compared with the results obtained from other relativistic and nonrelativistic density functional. The comparison shows that the DRHBc theory with PC-PK1 provides an excellent microscopic description for the masses of even-$Z$ nuclei. The systematics of the nucleon separation energies, odd-even mass differences, pairing energies, two-nucleon gaps, $α$ decay energies, rms radii, quadrupole deformations, potential energy curves, neutron density distributions, and neutron mean-field potentials are discussed.

nucl-th↗

Gamow-Teller strength distributions of 18O and well-deformed nuclei 24,26Mg by deformed QRPA

We investigate the Gamow-Teller (GT) transition strength distributions of {strongly} deformed nuclei, $^{24,26}$Mg, as well as of $^{18}$O. The calculations are performed within a deformed quasi-particle random phase approximation (DQRPA) which explicitly includes the deformation degree of freedom in the Skyrme-Hartree-Fock (SHF) and RPA calculations. The residual particle-particle ($p-p$) interaction as well as the particle-hole ($p-h$) interaction are extracted from Brückner $G$-matrix calculations. The {residual interaction} dependence of the low-lying GT strength of these strongly deformed nuclei is examined by changing the strength of the residual $p-p$ and $p-h$ interactions. We have found that the low-lying GT peaks are quite similar in energy to those found in {spherical} $N=Z$ and $N=Z+2$ nuclei near magic shells, but the configurations {of $^{24,26}$Mg are largely mixed by} the pairing correlations and the deformation. Our results are compared to the experimental GT $(\pm)$ transition data by ($t$, $^3$He) and ($^{3}$He, $t$) reactions, {and found to reproduce the main features of GT strength distributions.

nucl-th↗

Nuclear shape evolution of neutron-deficient Au and kink structure of Pb isotopes

Recent experiments using advanced laser spectroscopy technique revealed that the charge radii of neutron-deficient gold (Au) isotopes exhibit significant changes in ground state deformation: odd-even shape staggering in the $N = 98 \sim 100$ region and abrupt change of charge radii from $N =$ 108. In this study, we examine the abnormal shape evolution of the nuclear charge radii. To understand the nuclear structure underlying this phenomenon, we exploit the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). The significant change in mean-squared charge radii ($δ{< r^2 >}$) turns out to originate from nuclear shape transitions between prolate deformation and small oblate deformation due to the shape coexistence possibility. We elucidate the nuclear shape evolution by analyzing the evolution of occupation probability for single-particle states. In addition, the abrupt kink structure in the nuclear charge radius of lead (Pb) isotopes near the $N =$ 126 shell is also investigated and reproduced quite well.

nucl-th↗

Symmetry Energy from Two-Nucleon Separation Energies of Pb and Ca Isotopes

We investigate the symmetry energy in relation with the two-proton and two-neutron separation energies using different nuclear mass data. For this aim, we exploit the deformed relativistic Hartree-Bogoliubov theory in the continuum (DRHBc), FRDM2012 and AME2020 data. First, we study the two-proton and two-neutron separation energies in Pb and Ca isotopes by subtracting the contribution of Coulomb energy. They show a strong correlation with neutron number as well as with the neutron skin thickness. By taking the relative difference of both separation energies, we derive the symmetry energy from Ca and Pb isotopes. Since the nuclear surface contributes to the symmetry energy, we deduce the volume symmetry energy by subtracting the surface contribution using several mass models. The obtained symmetry energy coefficient, $a_{sym}$, is 20.0 $\sim $ 22.7 MeV for Pb isotopes and 18.7 $\sim$ 19.3 MeV for Ca isotopes from the DRHBc mass table data, while the results from other mass tables are 19.6 $\sim$ 22.1 (20.7 $\sim$ 22.3) MeV for Pb isotopes and 18.9 $\sim$ 19.0 (19.6 $\sim$ 19.7) MeV for Ca isotopes from AME2020 (FRDM2012) data. The volume contribution to the asymmetry coefficient, $a_{sym}^v$, which depends on the ratio of the surface to the volume energy coefficients, $a_s / a_v$, is also provided for each mass model. Since the ratio $a_s / a_v$ is neither determined by nuclear theory, nor by experimental data, we have investigated $a_{sym}^v$ by using the ratio $a_s / a_v$ as a free parameter, and have obtained $a_{sym}^v = $ 27.0 MeV, almost irrespective of nuclear model and isotopic chain, with the ratio $a_s / a_v$ constrained as $a_s / a_v = 1.10 \sim 1.13$.

nucl-th↗

Residual Tensor Force Effects on the Gamow-Teller states in Magic Nuclei, 48Ca, 90Zr, 132Sn, and 208Pb

We investigate the tensor force (TF) effect %in the residual interaction on the Gamow-Teller (GT) transitions in four magic nuclei, $^{48}$Ca, $^{90}$Zr, $^{132}$Sn and $^{208}$Pb. The TF is taken into account by using the Brückner $G$-matrix theory with the charge-dependent (CD) Bonn potential as the residual interaction of charge-exchange quasiparticle random phase approximation (QRPA). We found that particle-particle ($p-p$) tensor interaction does not affect the GT transitions because of the closed shell nature in the nuclei, but repulsive particle-hole ($p-h$) residual interaction for the $p-h$ configuration of spin-orbit partners dominates the high-lying giant GT states for all of the nuclei. It is also shown that appreciable GT strengths are shifted to lower energy region by the attractive $p-h$ TF for the same $j_π=j_ν$ configuration, and produce the low-lying GT peak about 2.5 MeV in $^{48}$Ca. Simultaneously, in $^{90}$Zr and $^{132}$Sn, the low-energy strength appears as a lower energy shoulder near the main GT peak. On the other hand, the shift of the low-lying GT state is not seen clearly for $^{208}$Pb because of the strong spin-orbit splitting of high $j$ orbits, which dominates the GT strength.

nucl-th↗

Suppression of the elastic scattering cross section for 17Ne + 208Pb system

We investigated the elastic scattering, inelastic scattering, breakup reaction, and total fusion reactions of 17Ne + 208Pb system using the optical model (OM) and a coupled channel (CC) approaches. The aim of this study is to elucidate the suppress of the elastic cross-section that is invisible in proton-rich nuclei such as 8B and 17F projectiles but appears in neutron-rich nuclei such as 11Li and 11Be projectiles. The results revealed that this suppression was caused mainly by the nuclear interaction between the projectile and target nucleus rather than the strong Coulomb interaction observed in neutron-rich nuclei and the contributions of Coulomb excitation interaction due to two low-lying E2 resonance states are relatively small. From the simultaneous chi-square analysis of the 17Ne + 208Pb system, we can infer a strong suppression effect in the elastic scattering cross-section due to the nuclear interaction between the projectile and target nucleus, rather than the Coulomb interaction as observed in neutron-rich nuclei. Also, the contribution of the direct reaction, comprising the inelastic scattering and breakup reaction cross-sections, accounted for almost half of the total reaction. Finally, we perform the CC calculation using the parameters obtained from our OM calculation but our CC calculations could not explain the 15O production cross section.

nucl-th↗

Effects of center-of-mass correction and nucleon anomalous magnetic moments on nuclear charge radii

Effects of the center-of-mass correction together with the nucleon electromagnetic form factors on the nuclear charge radius are systematically studied with a relativistic Hartree-Bogoliubov model. Both one- and two-body parts of the CM correction are taken into account. It is found that the one- and two-body CM corrections, and the spin-orbit effect originating from the nucleon anomalous magnetic moments are all of the same order in magnitude, and that they give sizable impacts on the charge radius from light to heavy nuclei.

nucl-th↗

Odd-even shape staggering and kink structure of charge radii of Hg isotopes by the deformed relativistic Hartree-Bogoliubov theory in continuum

We examined the shape staggering of relative charge radii in $^{180 - 186}$Hg isotopes, which was first measured in 1977 and recently confirmed using advanced spectroscopy techniques. To understand the nuclear structure underlying this phenomenon, we employed the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc). Our analysis revealed that the shape staggering can be attributed to nuclear shape transition in the Hg isotopes. Specifically, we demonstrated that prolate shapes of $^{181,183,185}$Hg lead to an increase in the charge radii compared to oblate shapes of $^{180,182,184,186}$Hg isotopes. We explained the nuclear shape staggering in terms of the evolution of occupation probability (OP) of $ν1 i_{13/2}$, $ν1 h_{9/2}$, $π1 h_{9/2}$, and $π3 s_{1/2}$ states. Additionally, we clarified the kink structure of the charge radii in the Hg isotopes near $N = 126$ magic shell does not come from the change of the OP of $π1 h_{9/2}$ state, but mainly by the increase of the OPs of $ν1 i_{11/2}$ and $ν2 g_{9/2}$ states.

nucl-th↗

$ΛΛ$ 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 $2\;M_\odot$.

nucl-th↗