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Yongseok Oh

Publications and source records attributed to Yongseok Oh.

At least 37 records · Page 2Linked to original sources
arXiv2018

Impact of medium modification of the nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter

Impact of the in-medium modified nucleon weak and electromagnetic form factors on the neutrino mean free path in dense matter is studied by considering both the weak and electromagnetic interactions of neutrinos with the constituents of the matter. A relativistic mean field model and the quark-meson coupling model are respectively adopted for the in-medium effective nucleon mass and nucleon form factors. We find that the cross sections of neutrino scattering in cold nuclear medium decreases when the in-medium modification of the nucleon weak and electromagnetic form factors are taken into account. This reduction results in the enhancement of the neutrino mean free path, in particular at the baryon density of around a few times of the normal nuclear matter density. The enhancement of the neutrino mean free path is estimated to be about 10--40\% compared with the values obtained without the medium modification of the nucleon form factors, and the enhancement is expected to accelerate the cooling of neutron stars.

nucl-th↗
arXiv2017

Effective interactions of hyperons and mass-radius relation of neutron stars

We examine the role of hyperons in a neutron star based on the relativistic mean field approach. For nuclear matter below 1.5 times the normal nuclear density we constrain the model parameters by using the symmetric nuclear matter properties and theoretical investigations for neutron matter in the literature. We then extend the model to higher densities by including hyperons and isoscalar vector mesons that contain strangeness degree of freedom. We confirm that the $ϕ$ meson induces a $Λ$ repulsive force and hardens the equation of state. The hardening arising from the $ϕ$ meson compensates the softening from the existence of hyperons. The flavor SU(3) and spin-flavor SU(6) relations are examined as well. We found that the coupling constants fitted by neutron matter properties could yield high enough maximum mass of a neutron star and the obtained results satisfy both the mass and radius constraints. The onset of the hyperon direct Urca process in neutron stars is also investigated using our parametrization.

nucl-th↗
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.

nucl-th↗
arXiv2017

Nuclear energy density functional and the nuclear alpha decay

The nuclear $α$ decay of heavy nuclei is investigated based on the nuclear energy density functional, which leads to the $α$ potential inside the parent nucleus in terms of the proton and neutron density profiles of the daughter nucleus. We use the Skyrme force model, Gogny force model, and relativistic mean field model to get the nucleon density profiles inside heavy nuclei. Once the nucleon density profiles are determined, the parameters of the nuclear $α$ potential are fitted to the observed $α$ decay half-lives of heavy nuclei. This approach is then applied to predict unknown $α$ decay half-lives of heavy nuclei. To estimate the $Q$ values of unobserved $α$ decays, we make use of the liquid droplet model.

nucl-th↗
arXiv2017

Decay angular distributions of $K^*$ and $D^*$ vector mesons in pion-nucleon scattering

The production mechanisms of open strangeness ($K^*$) and open charm ($D^*$) vector mesons in $π^- p$ scattering, namely, $π^- +p \to K^{*0} + Λ$ and $π^- + p \to D^{*-} + Λ_c^+$, are investigated within the modified quark-gluon string model. In order to identify the major reaction mechanisms, we consider the subsequent decays of the produced vector mesons into two pseudoscalar mesons, i.e., $K^* \to K + π$ and $D^* \to D + π$. We found that the decay distributions and density matrix elements are sensitive to the production mechanisms and can be used to disentangle the vector trajectory and pseudoscalar trajectory exchange models. Our results for $K^*$ production are compared with the currently available experimental data and the predictions for $D^*$ production processes are presented as well. Our predictions can be tested at the present or planned experimental facilities.

nucl-th↗
arXiv2016

Nuclear isospin asymmetry in $α$ decays of heavy nuclei

The effects of nuclear isospin asymmetry on $α$ decay lifetimes of heavy nuclei are investigated within various phenomenological models of nuclear potential for the $α$ particle. We consider the widely used simple square well potential and Woods-Saxon potential, and modify them by including an isospin asymmetry term. We then suggest a model for the potential of the $α$ particle motivated by a microscopic phenomenological approach of the Skyrme force model, which naturally introduce the isospin dependent form of the nuclear potential for the $α$ particle. The empirical $α$ decay lifetime formula of Viola and Seaborg is also modified to include isospin asymmetry effects. The obtained $α$ decay half-lives are in good agreement with the experimental data and we find that including the nuclear isospin effects somehow improves the theoretical results for $α$ decay half-lives. The implications of these results are discussed and the predictions on the $α$ decay lifetimes of superheavy elements are also presented.

nucl-th↗
arXiv2016

Regge approach to the reaction of $γN \to K^* Λ$

Photoproduction of $K^*$ vector mesons off nucleon is investigated within the Regge framework where the electromagnetic vertex of $γK^*K^*$ fully takes into account the magnetic dipole and electric quadrupole moments of spin-1 $K^*$ vector meson. The $t$-channel $K^*(892)$, $K(494)$ and $κ(800)$ meson exchanges are considered for the analysis of the production mechanism. The experimentally observed rapid decrease of the cross sections for the $γp \to K^{*+} Λ$ reaction beyond the resonance region is well reproduced by the dominance of the exchange of $K$-meson trajectory. The role of the scalar $κ$-meson trajectory is found to be minor in both $γp$ and $γn$ reactions. The cross sections for the $γn \to K^{*0} Λ$ reaction are predicted to be about twice those of the $γp \to K^{*+}Λ$ reaction. The role of the $K^*$ electromagnetic multipoles and the proton anomalous magnetic moment is studied through the total and differential cross sections and spin/parity asymmetries. We suggest the measurement of the photon polarization asymmetry as a tool for identifying the role of the magnetic dipole and electric quadrupole moments of the $K^*$ vector meson.

hep-ph↗
arXiv2015

Non-perturbative collisional energy loss of heavy quarks in quark-gluon plasma

We suggest a new mechanism for the energy loss of fast heavy quarks in quark-gluon plasma. This mechanism is based on pion production caused by the anomalous chromomagnetic quark-gluon-pion interaction induced by strong topological fluctuations of the gluon fields represented by instantons. We found that this mechanism gives a considerable contribution to the collisional energy loss of a heavy quark in quark-gluon plasma, which shows a nontrivial role of nonperturbative phenomena in strongly interacting quark-gluon plasma.

hep-ph↗
arXiv2015

Peculiarities of quasifission reactions in heavy ion collisions

The probability of the formation and decay of a dinuclear system is investigated for a wide range of relative orbital angular momentum values. The mass and angular distributions of the quasifission fragments are studied to understand the reaction mechanisms of the heavy ion collision of $^{78}$Kr(10$A$ MeV) + $^{40}$Ca within dinuclear system model. The quasifission products are found to contribute to the mass-symmetric region of the mass distribution in collisions with a large orbital angular momentum. The analysis of mass and angular distributions of quasifission fragments shows the possibility of the $180^\circ$ rotation of the system so that projectile-like products can be observed in the forward hemisphere with large cross sections, which can explain the phenomenon observed recently in the ISODEC experiment.

nucl-th↗
arXiv2015

Investigation of the $nnΛ$ bound state in pionless effective theory

The possibility of an $nnΛ$ bound state is investigated in the framework of pionless effective field theory at leading order. A system of coupled integral equations are constructed in the spin-isospin basis, of which numerical solutions are investigated. In particular, we make use of the limit cycle behavior, i.e., cyclic singularities of coupled integral equations of the system, which would be associated with the formation of a three-body bound state, so-called the Efimov state, in the unitary limit. Furthermore, we find that, when the sharp momentum cutoff introduced in the integral equations is taken significantly larger than the hard scale of the effective theory, the coupling of a three-body contact interaction becomes cyclically singular indicating the onset of Efimov-like bound state formation. However, the paucity of empirical information to determine the parameters of the theory precludes a definitive conclusion on the existence of such a bound state. As a simple test of the feasibility of the $nnΛ$ bound system in nature, we explore the cutoff dependence of the theory, and uncertainties of the present study are discussed as well.

nucl-th↗
arXiv2015

$\bar{K} + N \to K + Ξ$ reaction and $S=-1$ hyperon resonances

The $\bar{K} + N \to K + Ξ$ reaction is studied for center-of-momentum energies ranging from threshold to 3 GeV in an effective Lagrangian approach that includes the hyperon $s$- and $u$-channel contributions as well as a phenomenological contact amplitude. The latter accounts for the rescattering term in the scattering equation and possible short-range dynamics not included explicitly in the model. Existing data are well reproduced and three above-the-threshold resonances were found to be required to describe the data, namely, the $Λ(1890)$, $Σ(2030)$, and $Σ(2250)$. For the latter resonance we have assumed the spin-parity of $J^P=5/2^-$ and a mass of 2265 MeV. The $Σ(2030)$ resonance is crucial in achieving a good reproduction of not only the measured total and differential cross sections, but also the recoil polarization asymmetry. More precise data are required before a more definitive statement can be made about the other two resonances, in particular, about the $Σ(2250)$ resonance that is introduced to describe a small bump structure observed in the total cross section of $K^- + p \to K^+ + Ξ^-$. The present analysis also reveals a peculiar behavior of the total cross section data in the threshold energy region in $K^- + p \to K^+ + Ξ^-$, where the $P$- and $D$-waves dominate instead of the usual $S$-wave. Predictions for the target-recoil asymmetries of the $\bar{K} + N \to K + Ξ$ reaction are also presented.

nucl-th↗
arXiv2015

A study of the almost sequential mechanism of true ternary fission

We consider the collinear ternary fission which is a sequential ternary decay with a very short time between the ruptures of two necks connecting the middle cluster of the ternary nuclear system and outer fragments. In particular, we consider the case where the Coulomb field of the first massive fragment separated during the first step of the fission produces a lower pre-scission barrier in the second step of the residual part of the ternary system. In this case, we obtain a probability of about $10^{-3}$ for the yield of massive clusters such as \nuclide[70]{Ni}, \nuclide[80-82]{Ge}, \nuclide[86]{Se}, and \nuclide[94]{Kr} in the ternary fission of \nuclide[252]{Cf}. These products appear together with the clusters having mass numbers of $A = 132$--$140$. The results show that the yield of a heavy cluster such as \nuclide[68-70]{Ni} would be followed by a product of $A = 138$--$148$ with a large probability as observed in the experimental data obtained with the FOBOS spectrometer at the Joint Institute for Nuclear Research. The third product is not observed. The landscape of the potential energy surface shows that the configuration of the Ni + Ca + Sn decay channel is lower about 12 MeV than that of the Ca + Ni + Sn channel. This leads to the fact, that the yield of Ni and Sn is large. The analysis on the dependence of the velocity of the middle fragment on mass numbers of the outer products leads to the conclusion that, in the collinear tripartition channel of \nuclide[252]{Cf}, the middle cluster has a very small velocity, which does not allow it to be found in experiments.

nucl-th↗
arXiv2014

${}^{\ \ \ 6}_{ΛΛ} He$ in cluster effective field theory

The hypernucleus $\nuclide[6][ΛΛ]{He}$ is studied as a three-body ($ΛΛα$) cluster system in cluster effective field theory at leading order. We find that the three-body contact interaction exhibits the limit cycle when the cutoff in the integral equations is sent to the asymptotic limit, and thus it should be promoted to leading order. We also derive a determination equation of the limit cycle which reproduces the numerically obtained limit cycle. We then study the correlations between the double $Λ$ separation energy $B_{ΛΛ}^{}$ of $\nuclide[6][ΛΛ]{He}$ and the scattering length $a_{ΛΛ}^{}$ of the $S$-wave $ΛΛ$ scattering. The role of the scale in this approach is also discussed.

nucl-th↗
arXiv2014

Dense baryonic matter in conformally-compensated hidden local symmetry: Vector manifestation and chiral symmetry restoration

We find that, when the dilaton is implemented as a (pseudo-)Nambu-Goldstone boson using a conformal compensator or "conformon" in a hidden gauge symmetric Lagrangian written to $O(p^4)$ from which baryons arise as solitons, namely, skyrmions, the vector manifestation and chiral symmetry restoration at high density predicted in hidden local symmetry theory --- which is consistent with Brown-Rho scaling --- are lost or sent to infinite density. It is shown that they can be restored if in medium the behavior of the $ω$ field is taken to deviate from that of the $ρ$ meson in such a way that the flavor $U(2)$ symmetry is strongly broken at increasing density. The hitherto unexposed crucial role of the $ω$ meson in the structure of elementary baryon and multibaryon systems is uncovered in this work. In the state of half-skyrmions to which the skyrmions transform at a density $n_{1/2}^{} \gtrsim n_0^{}$ (where $n_0^{}$ is the normal nuclear matter density), characterized by the vanishing (space averaged) quark condensate but nonzero pion decay constant, the nucleon mass remains more or less constant at a value $\gtrsim$ 60 \% of the vacuum value indicating a large component of the nucleon mass that is not associated with the spontaneous breaking of chiral symmetry. We discuss its connection to the chiral-invariant mass $m_0^{}$ that figures in the parity-doublet baryon model.

hep-ph↗
arXiv2014

Four-quark structure of the excited states of heavy mesons

We propose a four-quark structure for some of the excited states of heavy mesons containing a single charm or bottom quark. The four-quark wave functions are constructed based on a diquark-antidiquark form under the constraint that they form an antitriplet $\bar{\bf{3}}_f$ in $\mbox{SU(3)}_f$, which seems to be realized in some of the excited states listed in Particle Data Group. Depending on the structure of antidiquark, we construct two possible models for its wave functions: Model I) the antidiquark is symmetric in flavor ($\bar{\bf{6}}_f$) and antisymmetric in color ($\bf{3}_c$) and Model II) the antidiquark is antisymmetric in flavor ($\bf{3}_f$) and symmetric in color ($\bar{\bf{6}}_c$). To test phenomenological relevance of these wave functions, we calculate the mass differences among the excited states of spin $J=0,1,2$ using color-spin interactions. The four-quark wave functions based on Model~I is found to reproduce the observed mass of the excited states of heavy mesons. Also, our four-quark model provides an interesting phenomenology relating to the decay widths of the excited states. To further pursue the possibility of the four-quark structure, we make a few predictions for open charm and open bottom states that may be discovered in future experiments. Most of them are expected to have broad widths, which would make them difficult to be identified experimentally. However, one resonance with $J=1$ containing bottom and strange quarks is expected to appear as a sharp peak with its mass around $B^{\bar s}_{1N} \sim 5753$~MeV. Confirmation of the existence of such states in future experiments will shed light on our understanding of the structure of heavy meson excited states.

hep-ph↗
arXiv2014

Production cross section of neutron-rich isotopes with radioactive and stable beams

The production cross section of neutron-rich isotopes of Ca, Zn, Te, Xe, and Pt are predicted in the diffusive multi-nucleon transfer reactions with stable and radioactive beams. With these isotopes one can treat the neutron shell evolution beyond N = 28, 50, 82, and 126. Because of the small cross sections, the production of nuclei near the neutron drip line requires the optimal choice of reaction partners and bombarding energies.

nucl-th↗
arXiv2014

Skyrmions with vector mesons revisited

In order to develop a model that can describe both a single baryon and multi-baryon systems on the same footing, we re-investigate the Skyrme model in a chiral Lagrangian derived from the hidden local symmetry (HLS) up to $O(p^4)$ including the homogeneous Wess-Zumino terms. We use the master formulas that connect the parameters of the HLS Lagrangian and a class of holographic QCD models, which provides a controllable way to determine the low-energy constants of the Lagrangian once the pion decay constant and the vector meson mass are given. Therefore, this model allows us to study the role of vector mesons in the skyrmion structure. We find that the $ρ$ and $ω$ vector mesons have different roles in the skyrmion structure and that the $ω$ meson has an important role in the properties of the nucleon.

hep-ph↗