arXiv subjects

Bao Yuan Sun

Publications and source records attributed to Bao Yuan Sun.

At least 19 recordsLinked to original sources

arXiv2026

Single- and Double-$Λ$ Hypernuclear Correlations Calibrate $ΛΛ$ Interaction Energies

Double-$Λ$ hypernuclei are essential for probing the $ΛΛ$ interaction in the double-strangeness $S=-2$ sector, yet the scarcity of experimental data severely limits systematic predictions. We present an evaluation framework based on nuclear many-body theory that exploits the intrinsic structural similarity between single-$Λ$ and double-$Λ$ systems to transfer empirical constraints from the well-mapped $S = -1$ sector to the $S = -2$ sector. By analyzing theoretical deviations of binding energies in light single- and double-$Λ$ hypernuclei, we identify a robust linear correlation between two sectors. This correlation enables a statistical evaluation of double-$Λ$ separation energies ($B_{ΛΛ}$) and $ΛΛ$ interaction energies ($ΔB_{ΛΛ}$) for heavier double-$Λ$ hypernuclei, by drawing on a wealth of empirical data from the single-$Λ$ sector with quantified uncertainties. Our results show that evaluated $ΔB_{ΛΛ}$ values, while consistent with existing data, are systematically larger than direct relativistic density functional predictions constrained only by the NAGARA event. This discrepancy suggests that standard mean-field-based extrapolations may underestimate $ΛΛ$ correlations and other many-body effects, motivating an evaluation-based correction that offers crucial benchmarks for future $S = -2$ experiments at facilities such as HIAF and J-PARC.

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arXiv2025

Limits on dark matter existence in neutron stars from recent astrophysical observations and mass correlation analysis

Dark matter admixed neutron stars (DANSs) serve as a specific astrophysical laboratory for probing the features of dark matter (DM) and have emerged as a promising candidate for interpreting recent astrophysical observations (e.g., by NICER and LIGO/Virgo). Accurately constraining the internal DM content of DANSs is therefore of critical importance. In this work, we construct the equations of state (EoS) for DANS matter by employing twelve nuclear matter (NM) models within the covariant density functional (CDF) theory and a self-interacting fermionic model for DM. Using these EoSs as input, we solve the two-fluid Tolman-Oppenheimer-Volkov (TOV) equations to systematically investigate the influence of DM on the global properties of neutron stars (NSs). By incorporating recent observational constraints on NS properties, the maximum DM mass fraction $f_χ^{\mathrm{max}}$ in DANSs is determined for each NM EoS model. Our analysis reveals a strong linear correlation (Pearson coefficient $r=0.98$) between $f_χ^{\mathrm{max}}$ and the maximum mass of a pure NS, $M_{\rm{NS}}^{\mathrm{max}}$, described by $f_χ^{\mathrm{max}} = 0.22 M_{\mathrm{NS}}^{\mathrm{max}} - 0.44$. Leveraging this correlation and the observed NS maximum mass distribution, $P(M_{\text{NS}}^{\max} \mid \text{EM})$, we derive the probability distribution function (PDF) for the maximum DM mass, $P(M_χ^{\max} \mid \text{EM})$, in DANSs. We find that at the 68\% confidence level, $M_χ^{\mathrm{max}}=0.150^{+0.070}_{-0.051}\ M_{\odot}$. This quantitative constraint on the DM mass provides a critical prior for interpreting potential observational signatures of DANSs, such as anomalous tidal deformabilities and distinctive gravitational-wave signals.

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arXiv2025

Impact of $Ξ$-Hypernuclear Constraints on Relativistic Equation of State and Properties of Hyperon Stars

Significant uncertainties persist in describing the equation of state and internal structure of hyperon stars due to the limited understanding of the mechanisms underlying hyperon interactions. Constraining the interaction parameter space through a combination of the latest astronomical observations and hypernuclear physics experiments is therefore essential. In this study, we incorporate experimental constraints from $Ξ$ hypernuclear physics on top of $Λ$ hyperons considered in \citet{Sun2023APJ942.55}. Specifically, based on updated measurements of hyperon separation energies from $Ξ$ hypernuclear experiments, sets of $ΞN$ effective interactions are constructed and a linear correlation between their scalar ($σ$) and vector ($ω$) coupling strength ratios is proposed as a constraint derived from $Ξ$ hypernuclear physics. Together with experimental correlations and astronomical observational data, four types of analyses are performed to constrain hyperon-nucleon interactions and the properties of hyperon stars. Compared to the vector $ω$ meson-hyperon coupling, the introduction of linear correlations in hypernuclear physics imposes a more substantial constraint on the scalar $σ$ meson-hyperon coupling, significantly enhancing its coupling strength and thereby ensuring the stiffness of the equation of state, highlighting the crucial role of hypernuclear studies in solving the hyperon puzzle problem. Consequently, a maximum mass of around $2M_{\odot}$ can be achieved with all five interactions considered in this study under the combined constraints from astronomical observations and nuclear physics. With more reliably estimated hyperon-nucleon contributions, the uncertainties in both the fractions and the threshold densities at which hyperons appear inside neutron stars are notably reduced, along with those in the mass-radius predictions.

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arXiv2025

Impact of pion tensor force on alpha clustering in $^{20}$Ne

The nuclear clustering, as a quantum phase transition phenomenon governed by strong interactions, exhibits characteristics that are highly sensitive to the specific features of nuclear forces. Here, we examine how nuclear deformation and tensor forces influence $α$-cluster formation in light nuclei. The axially deformed relativistic Hartree-Fock-Bogoliubov model is utilized to investigate the clustering structure of the $^{20}$Ne nucleus, at both the ground state and the excited state with a superdeformed prolate. The nuclear binding energies and the canonical single particle levels are obtained at different quadruple deformation, and the role of tensor force embedded in the Fock diagram of $π$-pseudovector ($π$-PV) coupling is revealed. It is shown that the level branches from the degenerated spherical orbits at the deformed prolate case are enlarged due to the extra contribution from pion-exchanged tensor force. Correspondingly, the excitation energy in this superdeformed prolate state is reduced due to the noncentral tensor interaction, leading to a predicted value which is much closer to the referred threshold for the $2α$ decay mode of $^{20}$Ne. Possible $α$-clustering configurations in $^{20}$Ne are then characterized by examining the nucleonic localization function. Although the contribution to the ground state is relatively small, the density profile and nucleonic localization are significantly changed by the pion tensor force for the superdeformed prolate excited state, as further evidenced by characterising the level mixing in the spherical basis components. The results reveal the extra role of the tensor force, correlated to the evolved single-particle levels with nuclear deformation, in the formation and stability of nuclear clustering.

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arXiv2024

Density-dependent relativistic mean-field model for $ Ξ^{-} $ hypernuclei

In hypernuclear systems, interactions involving nucleons and hyperons are intricately influenced by the surrounding particles, particularly by the density and the isospin feature of the nuclear medium. In this work, the relativistic mean-field (RMF) theory is adopted to describe the structure of several typical $Ξ^{-}$ hypernuclei. New sets of $ΞN$ effective interactions, by taking a density-dependent meson-nucleon/hyperon coupling perspective, are developed by fitting experimental data on the $Ξ^{-}$ hyperon $1s$ and $1p$ state separation energy of $^{15}_{Ξ^{-}}$C as well as the $1p$ state separation energy of $^{13}_{Ξ^{-}}$B. The density-dependent behavior of meson-hyperon coupling strengths sensitively affects the description of hyperon single-particle levels. In fact, the density-dependent meson-baryon coupling strengths introduce additional rearrangement contributions to the hyperon self-energy. Correspondingly, detailed forms of density dependence in these coupling strengths and different considerations of meson-baryon coupling channels will impact the hyperon single-particle properties within hypernuclei. Especially with the additional inclusion of the isovector scalar $ δ$ meson, the significant enhancement of rearrangement terms in the effective interaction DD-ME$δ$ impacts the shape of the hyperon potential and alters the characteristics of the isovector channel dynamics balance in the effective nuclear force. Relevant research underscores the importance of precisely accounting for in-medium effects in hyperon-nucleon interactions and incorporating a more comprehensive set of meson-exchange degrees of freedom in effective nuclear forces, offering a potential solution for more self-consistently describing the featured hyperon single-particle behavior of various hypernuclei and for reducing uncertainties in theoretical descriptions.

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arXiv2024

Charmed hypernuclei within density-dependent relativistic mean-field theory

The charmed $ Λ_{c}^{+} $ hypernuclei are investigated within the framework of the density-dependent relativistic mean-field (DDRMF) theory. Starting from the empirical hyperon potential in symmetric nuclear matter, obtained through microscopic first-principle calculations, two sets of $Λ_c N$ effective interactions were derived by fitting the potentials with minimal uncertainty (Fermi momentum $k_{F,n} = 1.05~\rm{fm}^{-1}$) and near saturation density ($k_{F,n} = 1.35~\rm{fm}^{-1}$). These DDRMF models were then used to explore the $Λ_{c} N$ effective interaction uncertainties on the description of hypernuclear bulk and single-particle properties. A systematic investigation was conducted on the existence of bound $Λ_{c}^{+}$ hypernuclei. The dominant factors affecting the existence and stability of hypernuclei were analyzed from the perspective of the $Λ_{c}^{+}$ potential. It is found that the hyperon potential is not only influenced by the Coulomb repulsion, but by an extra contribution from the rearrangement terms due to the density dependence of the meson-baryon coupling strengths. Therefore, the rearrangement term significantly impacts the stability description for light hypernuclei, while for heavier hypernuclei, the contribution from Coulomb repulsion becomes increasingly significant and eventually dominant. The discussion then delves into the bulk and single-particle properties of charmed hypernuclei using these models. It is found that even when different models yield similar hyperon potentials for nuclear matter, different treatments of nuclear medium effects could lead to disparities in the theoretical description of hypernuclear structures. This study indicates that constraints on the $ Λ_{c} N $ interaction at finite densities are crucial for the study of $ Λ_{c}^{+} $ hypernuclear structures.

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arXiv2023

Density-dependent relativistic mean field approach and its application to single-$Λ$ hypernuclei in Oxygen isotopes

The in-medium feature of nuclear force which includes both nucleon-nucleon ($NN$) and hyperon-nucleon ($ΛN$) interactions impacts the description of single-$Λ$ hypernuclei. With the alternated mass number or isospin of hypernuclei, such effects could be unveiled by analyzing systematical evolution of the bulk and single-particle properties. From a density-dependent meson-nucleon/hyperon coupling perspective, a new $ΛN$ effective interaction in the covariant density functional (CDF) theory, namely DD-LZ1-$\Lambda1$, is obtained by fitting the experimental data of $Λ$ separation energies for several single-$Λ$ hypernuclei. It is then adopted to study the structure and transition properties of single-$Λ$ hypernuclei in Oxygen isotopes, comparing with several selected CDF Lagrangians. Discrepancy is observed explicitly in the isospin evolution of $\Lambda1p$ spin-orbit splitting with various effective interactions, ascribed to their divergence of the meson-hyperon coupling strengths with increasing density. In particular, the density-dependent CDFs introduce an extra contribution to enhance the isospin dependence of the splitting, which is originated from the rearrangement terms of $Λ$ self-energies. In addition, the characteristics of hypernuclear radii are studied along the isotopic chain. Owing to the impurity effect of $Λ$ hyperon, a size shrinkage is observed in the matter radii of hypernuclei as compared to their cores of normal nuclei, while its magnitude is elucidated further to correlate with the incompressibility of nuclear matter. Besides, there exists a sizable model-dependent trend that $Λ$ hyperon radii evolve with the neutron number, which is decided partly by the in-medium $NN$ interactions as well as the core polarization effects.

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arXiv2022

Unified neutron star EOSs and neutron star structures in RMF models

In the framework of Thomas-Fermi approximation, we study systematically the EOSs and microscopic structures of neutron star matter in a vast density range with $n_\mathrm{b}\approx 10^{-10}$-2 $\mathrm{fm}^{-3}$, where various covariant density functionals are adopted, i.e., those with nonlinear self couplings (NL3, PK1, TM1, GM1, MTVTC) and density-dependent couplings (DD-LZ1, DDME-X, PKDD, DD-ME2, DD2, TW99). It is found that the EOSs generally coincide with each other at $n_\mathrm{b}\lesssim 10^{-4}$ fm${}^{-3}$ and 0.1 fm${}^{-3}\lesssim n_\mathrm{b} \lesssim 0.3$ fm${}^{-3}$, while in other density regions they are sensitive to the effective interactions between nucleons. By adopting functionals with larger slope of symmetry energy $L$, the curvature parameter $K_\mathrm{sym}$ and neutron drip density generally increase, while the droplet size, proton number of nucleus, core-crust transition density, and onset density of non-spherical nuclei decrease. All functionals predict neutron stars with maximum masses exceeding the two-solar-mass limit, while those of DD2, DD-LZ1, DD-ME2, and DDME-X predict optimum neutron star radii according to the observational constraints. Nevertheless, the corresponding skewness coefficients $J$ are much lager than expected, while only the functionals MTVTC and TW99 meet the start-of-art constraints on $J$. More accurate measurements on the radius of PSR J0740+6620 and the maximum mass of neutron stars are thus essential to identify the functional that satisfies all constraints from nuclear physics and astrophysical observations. Approximate linear correlations between neutron stars' radii at $M=1.4 M_{\odot}$ and $2 M_{\odot}$, the slope $L$ and curvature parameter $K_\mathrm{sym}$ of symmetry energy are observed as well, which is mainly attributed to the curvature-slope correlations in the functionals adopted here.

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arXiv2022

Quenched Λ spin-orbit splitting by relativistic Fock diagram in single-Λ hypernuclei

We extend the relativistic Hartree-Fock (RHF) theory to study the structure of single-$Λ$ hypernuclei. The density dependence is taken in both meson-nucleon and meson-hyperon coupling strengths, and the induced $Λ$-nucleon ($ΛN$) effective interactions are determined by fitting $Λ$ separation energies to the experimental data for several single-$Λ$ hypernuclei. The equilibrium of nuclear dynamics described by the RHF model in normal atomic nuclei, namely, the balance between nuclear attractive and repulsive interactions, is then found to be drastically changed in single-$Λ$ hypernuclei, revealing a different role of Fock terms via $Λ$ hyperon from the nucleon exchange. Since only one hyperon exists in a single-$Λ$ hypernucleus, the overwhelmed $ΛN$ and $ΛΛ$ attractions via the Hartree than the $ΛΛ$ repulsion from the Fock terms require an alternation of meson-hyperon coupling strengths in RHF to rebalance the effective nuclear force with the strangeness degree of freedom, leading to an improved description of $Λ$ Dirac mass and correspondingly a systematically reduced $σ$-$Λ$ coupling strength $g_{σΛ}$ in current models as compared to those relativistic mean-field (RMF) approaches without Fock terms. As a result, the effective $Λ$ spin-orbit coupling potential in the ground state of hypernuclei is suppressed, and these RHF models predict correspondingly a quenching effect in $Λ$ spin-orbit splitting in comparison with the RMF cases. Furthermore, the $Λ$ spin-orbit splitting could decrease efficiently by evolving the hyperon-relevant couplings $g_{σΛ}$ and $g_{ωΛ}$ simultaneously, where to reconcile with the empirical value the RHF models address a larger parameter space of meson-hyperon couplings.

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arXiv2022

Unified nuclear matter EOSs constrained by the in-medium balance in density-dependent covariant density functionals

Considering the effects of charge screening, we propose a new numerical recipe within the framework of Thomas-Fermi approximation, where the properties of nuclear matter throughout a vast density range can be obtained self-consistently. Assuming spherical and cylindrical approximations for the Wigner-Seitz cell, typical nuclear matter structures (droplet, rod, slab, tube, bubble, and uniform) are observed. We then investigate the EOSs and microscopic structures of nuclear matter with both fixed proton fractions and $β$-equilibration, where two covariant density functionals DD-LZ1 and DD-ME2 are adopted. Despite the smaller slope $L$ of symmetry energy obtained with the functional DD-LZ1, the curvature parameter $K_\mathrm{sym}$ is much larger than that of DD-ME2, which is attributed to the peculiar density-dependent behavior of meson-nucleon couplings guided by the restoration of pseudo-spin symmetry around the Fermi levels in finite nuclei. Consequently, different mass-radius relations of neutron stars are predicted by the two functionals. Different microscopic structures of nonuniform nuclear matter are obtained as well, which are expected to affect various physical processes in neutron star properties and evolutions.

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arXiv2019

Critical parameters of liquid-gas phase transition in thermal symmetric and asymmetric nuclear matter

The properties of critical parameters and phase diagram structure of liquid-gas phase transition are investigated in thermal symmetric and asymmetric nuclear matter with the covariant density functional (CDF) theory. Although uncertainty remains in predicting the critical parameters such as the critical temperature and pressure from various CDF functionals, several correlations are explored numerically and verified to be approximately linear between them. These correlations become worse when nuclear matter is more isospin asymmetric, resulting mainly from the effects induced by symmetry energy. By looking over the isospin dependence of the critical temperature, the role of the symmetry energy in LG transition properties of asymmetric matter is realized. The change of critical temperature with isospin asymmetry is found to be correlated well with and as a consequence could be constrained by the density slope of symmetry energy at saturation density. Then, the structure of phase diagram of thermal nuclear matter is analyzed carefully. It is revealed that the contribution from symmetry energy dominates the size of liquid-gas phase coexistence area. Moreover, the specific pattern of the phase diagram could be determined by the critical temperature at non-zero isospin asymmetry, illustrated from the correlations of the temperature with pressures at several characteristic points, paving the possible way to further explore the structure of liquid-gas phase diagram of thermal nuclear matter.

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arXiv2019

Applicability of Relativistic Point-Coupling Models to Neutron Star Physics

Comparing with a wide range of covariant energy density functional models based on the finite-range meson-exchange representation, the relativistic mean-field models with the zero-range contact interaction, namely the relativistic point-coupling models, are still infrequent to be utilized in establishing nuclear equation of state (EoS) and investigating neutron star properties, although comprehensive applications and achievements of them in describing many nuclear properties both in ground and exited states are mature. In this work, the EoS of neutron star matter is established constructively in the framework of the relativistic point-coupling models to study neutron star physics. Taking two selected functionals DD-PC1 and PC-PK1 as examples, nuclear symmetry energies and several neutron star properties including proton fractions, mass-radius relations, the core-crust transition density, the fraction of crustal moment of inertia and dimensionless tidal deformabilities are discussed. A suppression of pressure of neutron star matter found in the functional PC-PK1 at high densities results in the difficulty of its prediction when approaching to the maximum mass of neutron stars. In addition, the divergences between two selected functionals in describing neutron star quantities mentioned above are still large, ascribing to the less constrained behavior of these functionals at high densities. Then it is expected that the constraints on the dense matter EoS from precise and massive modern astronomical observations, such as the tidal-deformabilities taken from gravitational-wave events, would be essential to improve the parameterizing of the relativistic point-coupling models.

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arXiv2018

Correlated structure of nuclear symmetry energy from covariant nucleon self-energy

Based on the Hugenholtz-Van Hove theorem, the symmetry energy $J$ and its density slope parameter $L$ are decomposed in terms of the nucleon self-energies within the covariant density functional (CDF) theory. It is found that two structural connections between the different ingredients of $J$ and $L$ construct the fundamental correlation between $L$ and $J$ in the relativistic covariant framework, while the additional contribution from the isovector scalar channel of nucleon-nucleon interaction and those from the second-order symmetry self-energies lead to a deviation, especially the latter limits severely its correlation coefficient and confidence level. In addition, the relationship between the Landau mass $M_L^*$ and the Dirac mass $M_D^*$ is approximated to a reliable linear correlation, which is demonstrate to be sensitive to the momentum dependence of the nucleon self-energies.

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arXiv2018

Moments of inertia of neutron stars in relativistic mean field theory: the role of the isovector scalar channel

With the inclusion of the isovector scalar channel in the meson-nucleon couplings, taking DD-ME$δ$ as an effective interaction, the moments of inertia of neutron stars possessing various stellar masses are studied within the density dependent relativistic mean field (RMF) theory. The isovector scalar channel contributes to the softening of the neutron-star matter equation of state (EOS) and therefore the reduction of the maximum mass and radius of neutron stars. Smaller values of the total moment of inertia $I$ and the crustal moment of inertia $Δ{I}$ are then obtained in DD-ME$δ$ via numerical procedure in comparison with those in other selected RMF functionals. In addition, the involvement of the isovector scalar channel lowers the thickness of the neutron star crust and its mass fraction as well. The sensitivity to both the crustal mass and stellar radius causes the crustal moment of inertia to be more obviously reduced than the total one, eventually leading to a suppression on the fraction of crustal moment of inertia $Δ{I}/I$ in DD-ME$δ$. The results indicate the crustal moment of inertia as a more sensitive probe of the neutron-star matter EOS than the total one, and demonstrate that the isovector scalar meson-nucleon couplings in the RMF theory could exert influence over the physics of pulsar glitches.

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arXiv2018

Nuclear fourth-order symmetry energy and its effects on neutron star properties in the relativistic Hartree-Fock theory

Adopting the density dependent relativistic mean-field (RMF) and relativistic Hartree-Fock (RHF) approaches, the properties of the nuclear fourth-order symmetry energy $S_4$ are studied within the covariant density functional (CDF) theory. It is found that the fourth-order symmetry energies are suppressed in RHF at both saturation and supranuclear densities, where the extra contribution from the Fock terms is demonstrated, specifically via the isoscalar meson-nucleon coupling channels. The reservation of $S_4$ and higher-order symmetry energies in the nuclear equation of state then affects essentially the prediction of neutron star properties, which is illustrated in the quantities such as the proton fraction, the core-crust transition density as well as the fraction of crustal moment of inertia. Since the Fock terms enhance the density dependence of the thermodynamical potential, the RHF calculations predict systematically smaller values of density, proton fraction and pressure at the core-crust transition boundary of neutron stars than density dependent RMF ones. In addition, a linear anti-correlation between the core-crust transition density $ρ_t$ and the density slope of symmetry energy $L$ is found which is then utilized to constrain the core-crust transition density as $ρ_t\thicksim[0.069, 0.098]~\rm{fm}^{-3}$ with the recent empirical information on $L$. The study clarifies the important role of the fourth-order symmetry energy in determining the properties of nuclear matter at extreme isospin or density conditions.

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arXiv2017

Relativistic interpretation on the nature of nuclear tensor force

The spin-dependent nature of the nuclear tensor force is studied in details within the relativistic Hartree-Fock approach. The relativistic formalism for the tensor force is supplemented with an additional Lorentz-invariant tensor formalism in $σ$-scalar channel, so as to take into account almost fully the nature of the tensor force brought about by the Fock diagrams in realistic nuclei. Specifically, the tensor sum rules are tested for the spin and pseudo-spin partners with/without nodes, to further understand the tensor force nature within relativistic model. It is shown that the interference between two components of nucleon spinors brings distinct violations on the tensor sum rules in realistic nuclei , which is mainly due to the opposite sign on $κ$ quantities of the upper and lower components as well as the nodal difference. Even though, the sum rules can be precisely reproduced if taking the same radial wave functions for the spin/pseudo-spin partners in addition to neglecting the lower/upper components, revealing clearly the nature of tensor force.

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arXiv2015

The Nuclear Tensor Interaction in Covariant Energy Density Functional

The origin of the nuclear tensor interaction in the covariant energy density functional (EDF) is presented in this work, associated with the Fock diagrams of Lorentz scalar and vector couplings. With this newly obtained relativistic formalism of the nuclear tensor interaction, more distinct tensor effects are found in the Fock diagrams of the Lorentz scalar and vector couplings, as compared to the Lorentz pseudo-vector and tensor channels. A unified and self-consistent treatment on both the nuclear tensor and spin-orbit interactions, which dominate the spin-dependent features of the nuclear force, is then achieved by the relativistic models. Moreover, careful analysis on the tensor strengths indicates the reliability of the nuclear tensor interaction in the covariant EDF for exploring the nuclear structure, excitation and decay modes.

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arXiv2014

Isospin coupling-channel decomposition of nuclear symmetry energy in covariant density functional theory

The isospin coupling-channel decomposition of the potential energy density functional is carried out within the covariant density functional theory, and their isospin and density dependence in particular the influence on the symmetry energy is studied. It is found that both isospin-singlet and isospin-triplet components of the potential energy play the dominant role in deciding the symmetry energy, especially when the Fock diagram is introduced. The results illustrate a quite different mechanism to the origin of the symmetry energy from the microscopic Brueckner-Hartree-Fock theory, and demonstrate the importance of the Fork diagram in the CDF theory, especially from the isoscalar mesons, in the isospin properties of the in-medium nuclear force at high density.

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