arXiv subjects

Lie-Wen Chen

Publications and source records attributed to Lie-Wen Chen.

At least 55 records · Page 3Linked to original sources

arXiv2021

Supernova Preshock Neutronization Burst as a Probe of Non-Standard Neutrino Interactions

Core-collapse supernova (CCSN) provides a unique astrophysical site for studying neutrino-matter interactions. Prior to the shock-breakout neutrino burst during the collapse of the iron core, a preshock $ν_e$ burst arises from the electron capture of nuclei and it is sensitive to the low-energy coherent elastic neutrino-nucleus scattering (CE$ν$NS) which dominates the neutrino opacity. Since the CE$ν$NS depends strongly on the non-standard neutrino interactions (NSI) which are completely beyond the standard model and yet to be determined, the detection of the preshock burst thus provides a clean way to extract the NSI information. Within the spherically symmetric general-relativistic hydrodynamic simulation for the CCSN, we investigate the NSI effects on the preshock burst. We find that the NSI can maximally enhance the peak luminosity of the preshock burst almost by a factor of three, reaching a value comparable with that of the shock-breakout burst. Future detection of the preshock burst will have critical implications on astrophysics, neutrino physics and physics beyond the standard model.

astro-ph.HE↗

arXiv2021

Probing nuclear structure with mean transverse momentum in relativistic isobar collisions

Transverse momentum ($p_{T}$) generation in relativistic heavy ion collisions is sensitive to the initial geometry and the final-state bulk evolution. We demonstrate with hydrodynamic calculations that the mean $p_T$ ratio ($R_{\langle p_{T}\rangle}$) between the highly similar isobar $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions is insensitive to the bulk evolution and remains sensitive to the small difference in the initial nuclear structure (neutron skin and deformation) between the Ru and Zr nuclei.We further find that nuclear deformation can produce an anticorrelation between $R_{\langle p_{T}\rangle}$ and eccentricity (or elliptic flow) in central collisions. These findings suggest that the $R_{\langle p_{T}\rangle}$ between the isobar systems can be used to measure the neutron skin thickness and deformation parameters, which can in turn constrain the nuclear symmetry energy slope parameter.

nucl-th↗

arXiv2021

Bayesian inference of strange star equation of state using the GW170817 and GW190425 data

The observations of compact star inspirals from LIGO/Virgo provide a valuable tool to study the highly uncertain equation of state (EOS) of dense matter at the densities in which the compact stars reside. It is not clear whether the merging stars are neutron stars or quark stars containing self-bound quark matter. In this work, we explore the allowed bag-model-like EOSs by assuming the merging stars are strange quark stars (SQSs) from a Bayesian analysis employing the tidal deformability observational data of the GW170817 and GW190425 binary mergers. We consider two extreme states of strange quark matter, either in nonsuperfluid or color-flavor locked (CFL) and find the results in these two cases essentially reconcile. In particular, our results indicate that the sound speed in the SQS matter is approximately a constant close to the conformal limit of $c/\sqrt{3}$. The universal relations between the mass, the tidal deformability and the compactness are provided for the SQSs. The most probable values of the maximum mass are found to be $M_{\rm TOV}=2.10_{-0.12}^{+0.12}~(2.15_{-0.14}^{+0.16})\,M_{\odot}$ for normal (CFL) SQSs at a $90\%$ confidence level. The corresponding radius and tidal deformability for a $1.4\,M_{\odot}$ star are $R_{\rm 1.4}= 11.50_{-0.55}^{+0.52}~({11.42}_{-0.44}^{+0.52})~\rm km$ and $Λ_{1.4}= {650}_{-190}^{+230}~({630}_{-150}^{+220})$, respectively. We also investigate the possibility of GW190814's secondary component $m_2$ of mass $2.59_{-0.09}^{+0.08}\,M_{\odot}$ being an SQS, and find that it could be a CFL SQS with the pairing gap $Δ$ larger than $244~\rm MeV$ and the effective bag parameter $B_{\rm eff}^{1/4}$ in the range of $170$ to $192$ MeV, at a $90\%$ confidence level.

astro-ph.HE↗

arXiv2021

Comparison of Heavy-Ion Transport Simulations: Mean-field Dynamics in a Box

Within the transport model evaluation project (TMEP) of simulations for heavy-ion collisions, the mean-field response is examined here. Specifically, zero-sound propagation is considered for neutron-proton symmetric matter enclosed in a periodic box, at zero temperature and around normal density. The results of several transport codes belonging to two families (BUU-like and QMD-like) are compared among each other and to exact calculations. For BUU-like codes, employing the test particle method, the results depend on the combination of the number of test particles and the spread of the profile functions that weight integration over space. These parameters can be properly adapted to give a good reproduction of the analytical zero-sound features. QMD-like codes, using molecular dynamics methods, are characterized by large damping effects, attributable to the fluctuations inherent in their phase-space representation. Moreover, for a given nuclear effective interaction, they generally lead to slower density oscillations, as compared to BUU-like codes. The latter problem is mitigated in the more recent lattice formulation of some of the QMD codes. The significance of these results for the description of real heavy-ion collisions is discussed.

nucl-th↗

arXiv2021

Bayesian inference on the isospin splitting of nucleon effective mass from giant resonances in $^{208}$Pb

From a Bayesian analysis of the electric dipole polarizability, the constrained energy of isovector giant dipole resonance, the peak energy of isocalar giant quadrupole resonance and the constrained energy of isocalar giant monopole resonance in $^{208}$Pb, we extract the isoscalar and isovector effective masses in nuclear matter at saturation density $ρ_0$ as $m_{s,0}^{\ast}/m=0.87_{-0.04}^{+0.04}$ and $m_{v,0}^{\ast}/m = 0.78_{-0.05}^{+0.06}$ at $90\%$ confidence level. The obtained constraints on $m_{s,0}^{\ast}$ and $m_{v,0}^{\ast}$ lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry $δ$ at $ρ_0$ as $m_{n-p}^* / m=(0.20^{+0.15}_{-0.14})δ$. In addition, the symmetry energy at the subsaturation density $ρ^{\ast}=0.05~\mathrm{fm}^{-3}$ is determined to be $E_{\mathrm{sym}}(ρ^{\ast})=16.7\pm1.3$ MeV at $90\%$ confidence level.

nucl-th↗

arXiv2020

Probing the neutron skin with ultrarelativistic isobaric collisions

Particle production in ultrarelativistic heavy ion collisions depends on the details of the nucleon density distributions in the colliding nuclei. We demonstrate that the charged hadron multiplicity distributions in isobaric collisions at ultrarelativistic energies provide a novel approach to determine the poorly known neutron density distributions and thus the neutron skin thickness in finite nuclei, which can in turn put stringent constraints on the nuclear symmetry energy.

nucl-th↗

arXiv2020

Nuclear liquid-gas phase transition with machine learning

The machine-learning techniques have shown their capability for studying phase transitions in condensed matter physics. Here, we employ the machine-learning techniques to study the nuclear liquid-gas phase transition. We adopt an unsupervised learning and classify the liquid and gas phases of nuclei directly from the final state raw experimental data of heavy-ion reactions. Based on a confusion scheme which combines the supervised and unsupervised learning, we obtain the limiting temperature of the nuclear liquid-gas phase transition. Its value $9.24\pm0.04~\rm MeV$ is consistent with that obtained by the traditional caloric curve method. Our study explores the paradigm of combining the machine-learning techniques with heavy-ion experimental data, and it is also instructive for studying the phase transition of other uncontrollable systems, like QCD matter.

nucl-th↗

arXiv2020

Nuclear collective dynamics in transport model with the lattice Hamiltonian method

We review the recent progress on studying the nuclear collective dynamics by solving the Boltzmann-Uehling-Uhlenbeck (BUU) equation with the lattice Hamiltonian method treating the collision term by the full-ensemble stochastic collision approach. This lattice BUU (LBUU) method has recently been developed and implemented in a GPU parallel computing technique, and achieves a rather stable nuclear ground-state evolution and high accuracy in evaluating the nucleon-nucleon (NN) collision term. This new LBUU method has been applied to investigate the nuclear isoscalar giant monopole resonances and isovector giant dipole resonances. While the calculations with the LBUU method without the NN collision term (i.e., the lattice Hamiltonian Vlasov method) describe reasonably the excitation energies of nuclear giant resonances, the full LBUU calculations can well reproduce the width of the giant dipole resonance of $^{208}$Pb by including a collisional damping from NN scattering. The observed strong correlation between the width of nuclear giant dipole resonance and the NN elastic cross section suggests that the NN elastic scattering plays an important role in nuclear collective dynamics, and the width of nuclear giant dipole resonance provides a good probe of the in-medium NN elastic cross section.

nucl-th↗

arXiv2020

Constraining the in-medium nucleon-nucleon cross section from the width of nuclear giant dipole resonance

We develop a new lattice Hamiltonian method for solving the Boltzmann-Uehling-Uhlenbeck (BUU) equation. Adopting the stochastic approach to treat the collision term and using the GPU parallel computing to carry out the calculations allows for a rather high accuracy in evaluating the collision term, especially its Pauli blocking, leading thus to a new level of precision in solving the BUU equation. Applying this lattice BUU method to study the width of giant dipole resonance (GDR) in nuclei, where the accurate treatment of the collision term is crucial, we find that the obtained GDR width of $^{208}{\rm Pb}$ shows a strong dependence on the in-medium nucleon-nucleon cross section $σ_{\rm NN}^*$. A very large medium reduction of $σ_{\rm NN}^*$ is needed to reproduce the measured value of the GDR width of $^{208}{\rm Pb}$ at the Research Center for Nuclear Physics in Osaka, Japan.

nucl-th↗

arXiv2020

Enhanced yield ratio of light nuclei in heavy ion collisions with a first-order QCD phase transition

Using a transport model that includes a first-order chiral phase transition between the partonic and the hadronic matter, we study the development of density fluctuations in the matter produced in heavy ion collisions as it undergoes the phase transition, and their time evolution in later hadronic stage of the collisions. Using the coalescence model to describe the production of deuterons and tritons from nucleons at the kinetic freeze out, we find that the yield ratio $ N_\text{t}N_\text{p}/ N_\text{d}^2$, where $N_\text{p}$, $N_\text{d}$, and $N_\text{t}$ are, respectively, the proton, deuteron, and triton numbers, is enhanced if the evolution trajectory of the produced matter in the QCD phase diagram passes through the spinodal region of a first-order chiral phase transition.

nucl-th↗

arXiv2019

Cold dilute nuclear matter with $α$-particle condensation in a generalized nonlinear relativistic mean-field model

We explore the thermodynamic properties of homogeneous cold (zero-temperature) nuclear matter including nucleons and $α$-particle condensation at low densities by using a generalized nonlinear relativistic mean-field (gNL-RMF) model. In the gNL-RMF model, the $α$-particle is included as explicit degree of freedom and treated as point-like particle with its interaction described by meson exchanges and the in-medium effects on the $α$ binding energy is described by density- and temperature-dependent energy shift with the parameters obtained by fitting the experimental Mott density. We find that below the dropping density $n_{\rm{drop}}$ ($\sim 3\times 10^{-3}$ fm$^{-3}$), the zero-temperature symmetric nuclear matter is in the state of pure Bose-Einstein condensate (BEC) of $α$ particles while the neutron-rich nuclear matter is composed of $α$-BEC and neutrons. Above the $n_{\rm{drop}}$, the fraction of $α$-BEC decreases with density and vanishes at the transition density $n_t$ ($\sim 8\times 10^{-3}$ fm$^{-3}$). Above the $n_t$, the nuclear matter becomes pure nucleonic matter. Our results indicate that the empirical parabolic law for the isospin asymmetry dependence of nuclear matter equation of state is heavily violated by the $α$-particle condensation in the zero-temperature dilute nuclear matter, making the conventional definition of the symmetry energy meaningless. We investigate the symmetry energy defined under parabolic approximation for the zero-temperature dilute nuclear matter with $α$-particle condensation, and find it is significantly enhanced compared to the case without clusters and becomes saturated at about $7$ MeV at very low densities ($\lesssim 10^{-3}$ fm$^{-3}$). The critical temperature for $α$-condensation in homogeneous dilute nuclear matter is also discussed.

nucl-th↗

arXiv2019

Ruling out the supersoft high-density symmetry energy from the discovery of PSR J0740+6620 with mass $2.14^{+0.10}_{-0.09}M_\odot$

Using the very recently reported mass $2.14^{+0.10}_{-0.09}M_\odot$ of PSR J0740+6620 together with the data of finite nuclei and the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, we show that the symmetry energy $E_{\rm sym}(n)$ cannot be supersoft so that it becomes negative at suprasaturation densities in neutron stars (NSs) and thus may make the NS have a pure neutron matter core. This is in contrast to the fact that using the mass $2.01 \pm 0.04 M_\odot$ of PSR J0348+0432 as the NS maximum mass cannot rule out the supersoft high-density $E_{\rm sym}(n)$. Furthermore, we find the stiffer high-density $E_{\rm sym}(n)$ based on the existence of $2.14M_\odot$ NSs leads to a strong constraint of $Λ_{1.4} \ge 348^{+88}_{-51}$ for the dimensionless tidal deformability of the canonical $1.4M_\odot$ NS.

nucl-th↗

arXiv2019

Comparison of heavy-ion transport simulations: Collision integral with pions and $Δ$ resonances in a box

We compare ten transport codes for a system confined in a box, aiming at improved handling of the production of $Δ$ resonances and pions, which is indispensable for constraining high-density symmetry energy from observables such as the $π^-/π^+$ yield ratio in heavy-ion collisions. The system in a box is initialized with nucleons at saturation density and at 60 MeV temperature. The reactions $NN\leftrightarrow NΔ$ and $Δ\leftrightarrow Nπ$ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. In the results of the numbers of $Δ$ and $π$, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of collisions and decays, that take place in the same time step. Better agreements are seen in the reaction rates and the number ratios among the isospin species of $Δ$ and $π$. These are, however, affected by the correlations, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in transport calculations. The uncertainty in the transport-code predictions of the $π^-/π^+$ ratio for the system initialized at n/p = 1.5, after letting the existing $Δ$ resonances decay, is found to be within a few percent, which is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.

nucl-th↗

arXiv2019

Pairing effects on neutron matter equation of state and symmetry energy at subsaturation densities

Within the framework of BCS theory and Skyrme-Hartree-Fock model, we employ various microscopic pairing gaps and effective pairing interactions to study pairing effects on the equation of state (EOS) of neutron matter and the symmetry energy at subsaturation densities. We find pairing effects may have considerable contributions to the EOS of neutron matter at very low densities ($\lesssim 0.02~\rm{fm}^{-3}$), while only have a small impact on the symmetry energy at subsatruation densities. In addition, the reliability of the parabolic approximation for the isospin asymmetry dependence of nuclear matter EOS with pairing correlations included is also discussed.

nucl-th↗

arXiv2019

Neutron Skin in CsI and Low-Energy Effective Weak Mixing Angle from COHERENT Data

Both the neutron skin thickness $ΔR_{np}$ of atomic nuclei and the low-energy neutrino-nucleon ($νN$) interactions are of fundamental importance in nuclear and particle physics, astrophysics as well as new physics beyond the standard model (SM) but largely uncertain currently, and the coherent elastic neutrino-nucleus scattering (CE$ν$NS) provides a clean way to extract their information. New physics beyond the SM may cause effectively a shift of the SM weak mixing angle $θ_W$ in low-energy $νN$ interactions, leading to an effective weak mixing angle $θ^*_W$. By analyzing the CE$ν$NS data of the COHERENT experiment, we find that while a one-parameter fit to the COHERENT data by varying $ΔR_{np}$ produces $ΔR^{\rm{CsI}}_{np} \simeq 0.68^{+0.91}_{-1.13}$ fm for CsI with an unrealistically large central value by fixing $\sin^2 θ^*_W$ at the low-energy SM value of $\sin^2θ_W^{\rm{SM}} = 0.23857$, a two-dimensional fit by varying $ΔR_{np}$ and $\sin^2 θ^*_W$ leads to a strong positive correlation between $ΔR_{np}$ and $\sin^2 θ^*_W$ with significantly smaller central values of $ΔR^{\rm {CsI}}_{np} \simeq 0.24_{-2.03}^{+2.30}$ fm and $\sin^2 θ^*_W = 0.21_{-0.10}^{+0.13}$. Although the uncertainty is too large to claim a determination of $ΔR^{\rm{CsI}}_{np}$ and $\sin^2 θ^*_W$, the present study suggests that the multi-dimensional fit is important in future analyses of high-precision CE$ν$NS data. The implication of the possible deviation of $\sin^2 θ^*_W$ from $\sin^2θ_W^{\rm{SM}}$ on new physics beyond the SM is also discussed.

hep-ph↗

arXiv2019

Relativistic self-energy decomposition of nuclear symmetry energy and equation of state of neutron matter within QCD sum rules

Abstract (abridged edition): Properties of the relativistic nucleon self-energy decomposition of the symmetry energy as well as the equation of state (EOS) of pure neutron matter (PNM) are explored systematically within the QCD sum rules (QCDSR). Our results in the present work have demonstrated that the QCDSR approach can be used to explore the properties of asymmetric nuclear matter (ANM) in a quantitative manner, at least in lower density region. The QCDSR approach establishes a bridge connecting the EOS of ANM and the non-perturbative QCD vacuum, and thus provides a useful way to understand the properties of dense nucleonic matter from non-perturbative QCD vacuum. These studies are helpful to investigate the QCD origins about the uncertainties of nucleonic matter properties, e.g., the uncertainties of the symmetry energy. On the other hand, the exact knowledge on the EOS of ANM extracted from experiments, observations and model-independent calculations is also very useful for understanding the quark/gluon condensates in nuclear medium, which can provide important information on the chiral symmetry restoration phase transition in nuclear matter as well as the in-medium effects of hadron properties.

nucl-th↗

arXiv2019

Equation of state of dense matter in the multimessenger era

While the equation of state (EOS) of symmetric nuclear matter (SNM) at suprasaturation densities has been relatively well constrained from heavy-ion collisions, the EOS of high-density neutron-rich matter is still largely uncertain due to the poorly known high-density behavior of the symmetry energy. Using the constraints on the EOS of SNM at suprasaturation densities from heavy-ion collisions together with the data of finite nuclei and the existence of $2M_\odot$ neutron stars from electromagnetic (EM) observations, we show that the high-density symmetry energy cannot be too soft, which leads to lower bounds on dimensionless tidal deformability of $Λ_{1.4} \ge 193$ and radius of $R_{1.4} \ge 11.1$ km for $1.4M_\odot$ neutron star. Furthermore, we find that the recent constraint of $Λ_{1.4} \le 580$ from the gravitational wave signal GW170817 detected from the binary neutron star merger by the LIGO and Virgo Collaborations rules out too stiff high-density symmetry energy, leading to an upper limit of $R_{1.4} \le 13.3$ km. All these terrestrial nuclear experiments and astrophysical observations based on strong, EM and gravitational measurements together put stringent constraints on the high-density symmetry energy and the EOS of SNM, pure neutron matter and neutron star matter.

nucl-th↗

arXiv2019

Nuclear collective dynamics in the lattice Hamiltonian Vlasov method

The lattice Hamiltonian method is developed for solving the Vlasov equation with nuclear mean-field based on the Skyrme pseudopotential up to next-to-next-to-next-to leading order. The ground states of nuclei are obtained through varying the total energy with respect to the density distribution of nucleons. Owing to the self-consistent treatment of initial nuclear ground state and the exact energy conservation in the lattice Hamiltonian method, the present framework of solving the Vlasov equation exhibits very stable nuclear ground state evolution. As a first application of the new lattice Hamiltonian Vlasov method, we explore the iso-scalar giant monopole and iso-vector giant dipole modes of finite nuclei. The obtained results are shown to be comparable to that from random-phase approximation and consistent with the experimental data, indicating the capability of the present method in dealing with the long-time near-equilibrium nuclear dynamics.

nucl-th↗