arXiv subjects

Ting-Ting Sun

Publications and source records attributed to Ting-Ting Sun.

30 records · Page 2Linked to original sources

arXiv2022

Deconfinement phase transition and quark condensate in compact stars

We investigate systematically the possible deconfinement phase transition from nuclear matter to quark matter in compact stars. The properties of nuclear matter are fixed by expanding its binding energy to the order of $ρ^3$, while those of quark matter are predicted by an equivparticle model. The Maxwell construction is then applied for the quark-hadron mixed phase. By confronting compact star structures with pulsar observations, we obtain several EOSs that are compatible with the latest observations while supporting quark cores inside the most massive stars. It is found that the quark core is rather small and does not emerge for compact stars with $M\lesssim 2M_\odot$. The in-medium quark condensate of the stellar matter in those stars are then extracted within the framework of an equivparticle model, which decreases nonlinearly with density. At larger densities with pure quark matter, the quark condensate is still large and does not necessary decrease with density, indicating significant nonperturbative contributions within the density regions covered by compact stars.

hep-ph↗

arXiv2021

Quark condensate and chiral symmetry restoration in neutron stars

Based on an equivparticle model, we investigate the in-medium quark condensate in neutron stars. Carrying out a Taylor expansion of the nuclear binding energy to the order of $ρ^3$, we obtain a series of EOSs for neutron star matter, which are confronted with the latest nuclear and astrophysical constraints. The in-medium quark condensate is then extracted from the constrained properties of neutron star matter, which decreases non-linearly with density. However, the chiral symmetry is only partially restored with non-vanishing quark condensates, which may vanish at a density that is out of reach for neutron stars.

nucl-th↗

arXiv2021

Searching for single-particle resonances with the Green's function method

Single-particle resonances in the continuum are crucial for studies of exotic nuclei. In this study, the Green's function approach is employed to search for single-particle resonances based on the relativistic-mean-field model. Taking $^{120}$Sn as an example, we identify single-particle resonances and determine the energies and widths directly by probing the extrema of the Green's functions. In contrast to the results found by exploring for the extremum of the density of states proposed in our recent study [Chin. Phys. C, 44:084105 (2020)], which has proven to be very successful, the same resonances as well as very close energies and widths are obtained. By comparing the Green's functions plotted in different coordinate space sizes, we also found that the results very slightly depend on the space size. These findings demonstrate that the approach by exploring for the extremum of the Green's function is also very reliable and effective for identifying resonant states, regardless of whether they are wide or narrow.

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arXiv2021

The equation of state and radial oscillations of neutron stars

We investigate radial oscillations of pure neutron stars and hybrid stars, employing equations of state of nuclear matter from Brueckner-Hartree-Fock theory, and of quark matter from the Dyson-Schwinger quark model, performing a Gibbs construction for the mixed phase in hybrid stars. We calculate the eigenfrequencies and corresponding oscillation functions. Our results for the zero points of the first-order radial oscillation frequencies give the maximum mass of stable neutron stars, consistent with the common criterion $dM/dρ_c=0$. Possible observations of the radial oscillation frequencies could help to learn more about the equation of state, predict the maximum mass of neutron stars more precisely, and indicate the presence of quark matter.

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arXiv2020

Study of single-particle resonant states with Green's function method

The relativistic mean field theory with the Green's function method is taken to study the single-particle resonant states. Different from our previous work [Phys.Rev.C 90,054321(2014)], the resonant states are identified by searching for the poles of Green's function or the extremes of the density of states. This new approach is very effective for all kinds of resonant states, no matter it is broad or narrow. The dependence on the space size for the resonant energies, widths, and the density distributions in the coordinate space has been checked and it is found very stable. Taking $^{120}$Sn as an example, four new broad resonant states $2g_{7/2}$, $2g_{9/2}$, $2h_{11/2}$ and $1j_{13/2}$ are observed, and also the accuracy for the width of the very narrow resonant state $1h_{9/2}$ is highly improved to be $1\times 10^{-8}$ MeV. Besides, our results are very close to those by the complex momentum representation method and the complex scaling method.

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arXiv2020

Evaluation of pion-nucleon sigma term in Dyson-Schwinger equation approach of QCD

We calculate the variation of the chiral condensate in medium with respect to the quark chemical potential and evaluate the pion-nucleon sigma term via the Hellmann-Feynman theorem. The variation of chiral condensate in medium are obtained by solving the truncated Dyson-Schwinger equation for quark propagator at finite chemical potential, with different models for the quark-gluon vertex and gluon propagator. We obtain the value of the sigma term $σ_{πN}$ = 62(1)(2) MeV, where the first represents the systematic error due to our different model for the quark-gluon vertex and gluon propagator and the second represents a statistical error in our linear fitting procedure.

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arXiv2019

Green's function method for the spin and pseudospin symmetries in the single-particle resonant states

We investigate the spin and pseudospin symmetry in the single-particle resonant states by solving the Dirac equation containing a Woods-Saxon potential with Green's function method. Taking double-magic nucleus $^{208}$Pb as an example, three spin doublets $3d$, $2h$, and $1j$ and three pseudospin doublets $3\tilde{p}$, $1\tilde{i}$, and $1\tilde{j}$ are obtained for the single-neutron resonant states. By analyzing the energy splittings, we find that the threshold effect plays an important role in resonant pseudospin doubles. Besides, there is a reversed level structure of pseudospin doublets in the continuum. Differently, all the width splittings of either the spin doublets or the pseudospin doublets are systematically positive and the splittings are very small except $1\tilde{j}$ doublet. Further studies show that the splittings of the energies and widths for the resonant (pseudo)spin doublets are independent. Besides, the similarity properties of the wave functions of the spin and pseudospin doublets still maintain well in resonant states.

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arXiv2019

Continuum Skyrme-Hartree-Fock-Bogoliubov theory with Green's function method for odd-$A$ nuclei

To study the exotic odd nuclear systems, the self-consistent continuum Skyrme-Hartree-Fock-Bogoliubov theory formulated with Green's function technique is extended to include blocking effects with the equal filling approximation. Detailed formula are presented.To perform the integrals of the Green's function properly, the contour paths $C_{\rm b}^{-}$ and $C_{\rm b}^{+}$ introduced for the blocking effects should include the blocked quasi-particle state but can not intrude into the continuum area. By comparing with the box-discretized calculations, the great advantages of the Green's function method in describing the extended density distributions, resonant states, and the couplings with the continuum in exotic nuclei are shown. Finally, taking the neutron-rich odd nucleus $^{159}$Sn as an example, the halo structure is investigated by blocking the quasi-particle state $1p_{1/2}$. It is found that it is mainly the weakly bound states near the Fermi surface that contribute a lot for the extended density distributions at large coordinate space.

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arXiv2019

Strangeness and $Δ$ resonance in compact stars with relativistic-mean-field models

We explore the effects of strangeness and $Δ$ resonance in baryonic matter and compact stars within the relativistic-mean-field (RMF) models. The covariant density functional PKDD is adopted for $N$-$N$ interaction, parameters fixed based on finite hypernuclei and neutron stars are taken for the hyperon-meson couplings, and the universal baryon-meson coupling scheme is adopted for the $Δ$-meson couplings. In light of the recent observations of GW170817 with the dimensionless combined tidal deformability $197 \leq \barΛ\leq 720$, we find it is essential to include the $Δ$ resonances in compact stars, and small $Δ$-$ρ$ coupling $g_{ρΔ}$ is favored if the mass $2.27{}_{-0.15}^{+0.17}\ M_\odot$ of PSR J2215+5135 is confirmed.

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arXiv2018

Interface effects of strange quark matter with density dependent quark masses

We study the interface effects in strangelets adopting mean-field approximation (MFA). Based on an equivparticle model, the linear confinement and leading-order perturbative interactions are included with density-dependent quark masses. By increasing the confinement strength, the surface tension and curvature term of strange quark matter (SQM) become larger, while the perturbative interaction does the opposite. For those parameters constrained according to the 2$M_\odot$ strange star, the surface tension is $\sim$2.4 MeV/fm${}^2$, while unstable SQM indicates a slightly larger surface tension. The obtained results are then compared with those predicted by the multiple reflection expansion (MRE) method. In contrast to the bag model case, it is found that MRE method overestimates the surface tension and underestimates the curvature term. To reproduce our results, the density of states in the MRE approach should be modified by proper damping factors.

hep-ph↗

arXiv2017

Massive neutron stars and $Λ$-hypernuclei in relativistic mean field models

Based on relativistic mean field (RMF) models, we study finite $Λ$-hypernuclei and massive neutron stars. The effective $N$-$N$ interactions PK1 and TM1 are adopted, while the $N$-$Λ$ interactions are constrained by reproducing the binding energy of $Λ$-hyperon at $1s$ orbit of $^{40}_Λ$Ca. It is found that the $Λ$-meson couplings follow a simple relation, indicating a fixed $Λ$ potential well for symmetric nuclear matter at saturation densities, i.e., around $V_Λ = -29.786$ MeV. With those interactions, a large mass range of $Λ$-hypernuclei can be well described. Furthermore, the masses of PSR J1614-2230 and PSR J0348+0432 can be attained adopting the $Λ$-meson couplings $g_{σΛ}/g_{σN}\gtrsim 0.73$, $g_{ωΛ}/g_{ωN}\gtrsim 0.80$ for PK1 and $g_{σΛ}/g_{σN}\gtrsim 0.81$, $g_{ωΛ}/g_{ωN}\gtrsim 0.90$ for TM1, respectively. This resolves the Hyperon Puzzle without introducing any additional degrees of freedom.

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arXiv2017

Green's function relativistic mean field theory for $Λ$ hypernuclei

The relativistic mean-field theory with Green's function method is extended to study $Λ$ hypernuclei. Taking hypernucleus $^{61}_Λ$Ca as an example, the single-particle resonant states for $Λ$ hyperons are investigated by analyzing density of states and the corresponding energies and widths are given. Different behaviors are observed for the resonant states, i.e., the distributions of the very narrow $1f_{5/2}$ and $1f_{7/2}$ states are very similar as bound states while that of the wide $1g_{7/2}$ and $1g_{9/2}$ states are like scattering states. Besides, the impurity effect of $Λ$ hyperons on the single-neutron resonant states are investigated. For most of the resonant states, both the energies and widths decrease with adding more $Λ$ hyperons due to the attractive $ΛN$ interaction. Finally, the energy level structure of $Λ$ hyperons in the Ca hypernucleus isotopes with mass number $A=53-73$ are studied, obvious shell structure and small spin-orbit splitting are found for the single-$Λ$ spectrum.

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