Relativistic Mean Field Research Articles

Tensor and isovector–isoscalar terms of relativistic mean field model: Impacts on neutron-skin thickness, charge radius, and nuclear matter

The origin of the neutron skin thickness, measured by the CREX and PREX collaborations as thin for 40Ca and thick for 28Pb, remains a mystery. We investigate the effects of tensor and nonlinear isovector–isoscalar terms in a relativistic mean-field model (RMF) on the properties of finite nuclei and nuclear matter. Tensor couplings are crucial for better quality binding energies of finite nuclei and charge radii for relatively heavy nuclei. However, for light nuclei, the tensor terms cannot improve the compatibility of charge radius predictions by the RMF model with experimental data. We find that parameter sets with a larger nonlinear isovector–isoscalar parameter, particularly η2ρ = 0.028, agree better with experimental data for Δrnp across light, medium, and heavy isotope chains. Using PT28, we calculate Δrnp for 208Pb as 0.214 fm, J as 33.078, and L as 58.426. Δrnp for 208Pb obtained using PT28 is consistent with the PREX-II data. Moreover, the corresponding values of J and L agree with the low L constraints. Meanwhile, the canonical mass radius predicted by PT28 aligns with the mass and radius data from the NICER collaboration. The combination of tensor and nonlinear isovector–isoscalar couplings in the RMF model provides accurate predictions for finite nuclei binding energies and relatively heavy nuclei charge radii, resulting in relatively thick Δrnp values for 208Pb without substantial L values.

Alpha clustering in 41, 45, 49Ca* nuclei formed in neutron induced reactions

The light neutron-rich nuclei play a vital role in nucleosynthesis process and the extent of alpha (α) clustering significantly influence the astrophysical rates. Thus, it is significant to explore the α clustering in these nuclei and in the present work, we have studied the α clustering in 41,45,49Ca* nuclei formed in neutron induced reactions within the dynamical cluster decay model (DCM). The results present that with progression towards neutron-rich 45Ca* and 49Ca* nuclei, there is a significant decrease in the α-cluster preformation factor P0. The inclusion of relativistic mean field theory (RMFT) based microscopic temperature-dependent binding energies (T.B.E.) within DCM, give relatively enhanced α-cluster preformation factor for 41,45,49Ca* nuclei compared to the case of macroscopic T.B.E. based upon Davidson mass formula. The cross-section associated with α-cluster emission depicts strong isospin dependence and falls off significantly with increasing neutron number of Ca* nuclei. Further, for the first time, we inculcate the microscopic nuclear potential constructed via folding the standard Fermi form fitted RMFT cluster densities and M3Y nucleon-nucleon interaction within the DCM. The neutron skin thickness of the Ar cluster, complementary to α-cluster, is varied and its effect upon the nuclear interaction potential and α-cluster preformation factor is analysed. The results present that with growing neutron skin of Ar cluster, the α-cluster preformation factor decreases. It explores a strong correlation among the neutron skin thickness and α-cluster preformation factor in light mass 41,45,49Ca* nuclear systems.

Influence of the tetraneutron on the EoS under core-collapse supernova and heavy-ion collision conditions

Context. Recently, a resonant state of four neutrons (tetraneutron) with an energy of E4n = 2.37 ± 0.38(stat) ± 0.44(sys) MeV and a width of Γ = 1.75 ± 0.22(stat) ± 0.30(sys) MeV was reported. Aims. In this work, we analyze the effect of including such an exotic state on the yields of other light clusters; these clusters not only form in astrophysical sites, such as core-collapse supernovae and neutron star (NS) mergers, but also in heavy-ion collisions. Methods. To this aim, we used a relativistic mean-field (RMF) formalism, where we consider in-medium effects in a two-fold way – that is, via the couplings of the clusters to the mesons, and via a binding energy shift – to compute the low-density equation of state (EoS) for nuclear matter at finite temperature and fixed proton fraction. We consider five light clusters – namely deuterons, tritons, helions, α-particles, and 6He – immersed in a gas of protons and neutrons, and we calculate their abundances and chemical equilibrium constants with and without the tetraneutron. We also analyze how the associated energy of the tetraneutron would influence such results. Results. We find that the low-temperature, neutron-rich systems are the ones most affected by the presence of the tetraneutron, making NSs excellent environments for their formation. Moreover, its presence in strongly asymmetric matter may increase the proton and α-particle fractions considerably. This may have an influence on the dissolution of the accretion disk of the merger of two NSs.

Density-dependent relativistic mean field approach and its application to single-Λ hypernuclei in oxygen hyperisotopes* *Supported by the Fundamental Research Funds for the Central Universities, Lanzhou University (lzujbky-2022-sp02, lzujbky-2023-stlt01), the National Natural Science Foundation of China (11875152, 12275111), and the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34000000)

The in-medium feature of nuclear force, which includes both nucleon-nucleon () and hyperon-nucleon () interactions, impacts the description of single-Λ hypernuclei. With the alternated mass number or isospin of hypernuclei, such effects may be unveiled by analyzing the systematic evolution of the bulk and single-particle properties. From a density-dependent meson-nucleon/hyperon coupling perspective, a new effective interaction in the covariant density functional (CDF) theory, namely, DD-LZ1-, is obtained by fitting the experimental data of Λ separation energies for several single-Λ hypernuclei. It is then used to study the structure and transition properties of single-Λ hypernuclei in oxygen hyperisotopes, in comparison with those determined using several selected CDF Lagrangians. A discrepancy is explicitly observed in the isospin evolution of spin-orbit splitting with various effective interactions, which is attributed to the divergence of the meson-hyperon coupling strengths with increasing density. In particular, the density-dependent CDFs introduce an extra contribution to reduce the value but enhance the isospin dependence of the splitting, which originates 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 the Λ hyperon, a size shrinkage is observed in the matter radii of hypernuclei compared with the cores of normal nuclei, and its magnitude is further elucidated to correlate with the incompressibility of nuclear matter. Moreover, there is a sizable model-dependent trend in which the Λ hyperon radii evolve with neutron number, which is decided partly by the in-medium interactions and core polarization effects.

Quarkyonic matter and quarkyonic stars in an extended relativistic mean field model

Quarkyonic matter and quarkyonic stars in an extended relativistic mean field model

Meson-Exchange Currents in Quasielastic Electron Scattering in a Generalized Superscaling Approach

We introduce a method for consistently incorporating meson-exchange currents (MEC) within the superscaling analysis with relativistic effective mass, featuring a new scaling variable, ψ*, and single-nucleon cross-sections derived from the relativistic mean field (RMF) model of nuclear matter. The single-nucleon prefactor is obtained from the 1p1h matrix element of the one-body current, combined with the two-body current, averaged over a momentum distribution of Fermi kind. The approach is applied to selected quasielastic cross-sectional data on 12C. The results reveal a departure from scaling behavior, yet, intriguingly, the data collapse into a discernible band that is parametrized using a simple function of ψ*. This calculation, as developed, is not intended to provide pinpoint precision in extracting nuclear responses. Instead, it offers a global description of the quasielastic data with a considerable level of uncertainty. However, this approach effectively captures the overall trends of the quasielastic data beyond the Fermi gas model with a minimal number of parameters. The model incorporates partially transverse enhancement of the response, as embedded within the relativistic mean field framework. However, it does not account for enhancements attributed to the combined effects of tensor correlations and MEC, given that the initial RMF model lacks these correlations. A potential avenue for improvement involves starting with a correlated Fermi gas model to incorporate additional enhancements into single-nucleon responses. This study serves as a practical demonstration of implementing such corrections.

Probing the impact of WIMP dark matter on universal relations, GW170817 posterior, and radial oscillations

ABSTRACT In this study, we investigate the impact of weakly interacting massive particles (WIMPs) dark matter (DM) on C–Λ universal relations, GW170817 posterior, and radial oscillations of neutron stars (NSs) by considering the interactions of uniformly trapped neutralinos as a DM candidate with the hadronic matter through the exchange of the Higgs boson within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM). The hadronic equation of state (EOS) is modelled using the relativistic mean-field (RMF) formalism with IOPB-I, G3, and quark–meson coupling (QMC)-RMF series parameter sets. The presence of DM softens the EOS at both the background and the perturbation levels that implies a small shift to the left in the posterior accompanied by a much larger jump in the left of the mass–radius curves with increasing DM mass. It is observed that EOSs with DM also satisfy the C–Λ universality relations among themselves but get slightly shifted to the right in comparison to that without considering DM. Additionally, we find that the inclusion of DM allows the mass–radius (M–R) curves to remain consistent with observational constraints for HESS J1731−347, indicating the possibility of classifying it as a dark matter-admixed neutron star (DMANS). Moreover, we explore the impact of DM on the radial oscillations of pulsating stars and investigate the stability of NSs. The results demonstrate a positive correlation between the mass of DM and the frequencies of radial oscillation modes.

Bayesian analysis of a relativistic hadronic model constrained by recent astrophysical observations

ABSTRACTWe use Bayesian analysis in order to constrain the equation of state for nuclear matter from astrophysical data related to the recent measurements from the NICER mission, LIGO/Virgo collaboration, and probability distributions of mass and radius from other 12 sources, including thermonuclear busters, and quiescent low-mass X-ray binaries. For this purpose, we base our study on a relativistic hadronic mean field model including an ω − ρ interaction. Our results indicate optimal ranges for some bulk parameters at the saturation density, namely, effective mass, incompressibility, and symmetry energy slope (L0). For instance, we find $L_0 = 50.79^{+15.16}_{-9.24}$ MeV (Case 1) and $L_0 = 75.06^{+8.43}_{-4.43}$ MeV (Case 2) in a 68 per cent confidence interval for the two cases analysed (different input ranges for L0 related to the PREX-II data). The respective parametrizations are in agreement with important nuclear matter constraints, as well as observational neutron star data, such as the dimensionless tidal deformability of the GW170817 event. From the mass–radius curves obtained from these best parametrizations, we also find the ranges of 11.97 km ≤ R1.4 ≤ 12.73 km (Case 1) and 12.34 km ≤ R1.4 ≤ 13.06 km (Case 2) for the radius of the $1.4\, \mathrm{M}_\odot$ neutron star.

Re-examination of β-decay in Hg, Pb and Po Isotopes

This study re-examines the effect of nuclear deformation on the calculated Gamow-Teller (GT) strength distributions of neutron-deficient (178−192Hg, 185−194Pb and 196−206Po) nuclei. The nuclear ground state properties and shape parameters were calculated using the Relativistic Mean Field model. Three different density-dependent interactions (D3C, DD-ME2 and DD-PC1) were used in the calculation. Estimated shape parameters were later used within the framework of deformed proton-neutron quasi-random phase approximations model, with a separable interaction, to calculate the GT strength distributions, half-lives and branching ratios for these neutron–deficient isotopes. It was concluded that half-lives and GT strength distributions vary considerably with change in shape parameter.

Surface and decay properties of newly synthesized 207,208Th isotopes for various α-decay chains

Considering various initial deformations, the ground, first excited, and second excited states binding energies are calculated using the effective field theory motivated relativistic mean-field based IOPB-I force parameter. The alpha decay chains for both the 207Th and 208Th are examined. As observed for both nuclei, it takes four subsequent α-particle emissions to reach the stable Pb nucleus. The half-lives determined by two widely used Viola-Seaborg and modified universal decay law formulas are compared with the available experimental data. The surface property-like symmetry energy is also predicted for these nuclei in the framework of the coherent density fluctuation model and establishes a connection between the decay behavior and the symmetry energy.

Correlation between the nuclear structure and reaction dynamics of Ar-isotopes as projectile using the relativistic mean-field approach

This theoretical study is devoted to bridging the gap between the nuclear structure and reaction dynamics and unravelling their impact on each other, considering the neutron-rich light mass 30−60Ar isotopes. Using the relativistic mean-field with the NL3⁎ parameter set, several bulk properties such as binding energies, charge radii, quadrupole deformation parameter, two neutron separation energy, and differential two neutron separation energy with the shell closure parameter are probed for the mentioned isotopic chain. For validation, the RMF (NL3⁎) results are compared with those obtained from the finite range droplet model (FRDM), Weizsäcker-Skyrme model with WS3, WS⁎ parameters, and the available experimental data. Most of the participating isotopes are found to be prolate in structure, and neutron shell closures are conspicuously revealed at N=14,20,40 but weakly shown at N=24,28,34. From our analysis, a central depletion in the nucleonic density is identified in 32 Ar and 42−58 Ar, indicating that they are possible candidates for a semi-bubble-like structure. Interestingly, these results are consistent with recent theoretical and experimentally measured data. Furthermore, using the Glauber model, the reaction cross-sections are determined by taking 26−48Ar as projectiles and stable targets such as 12C, 16O, 40Ca, 90Zr, 124,132Sn, 208Pb and 304120. Although there is no experimental evidence for the stability of 304120, it was predicted by Bhuyan and Patra (2012) [115] as a stable nucleus. A relatively higher cross-section value is noticed between 30 Ar and 32 Ar, which infers that 32Ar is the most stable isotope among the considered chain. Moreover, we noticed that the profile of the differential cross-sections and scattering angle are highly influenced by the mass of the target nuclei and the magnitude of the incident energy of the projectile nucleus.

Neutron star properties in the (axial)vector meson extended linear sigma model

AbstractThe equation of state provided by effective models of strongly interacting matter should comply with the restrictions imposed by current astrophysical observations on compact stars. We explore the possibility, that there is quark matter in the center of neutron stars. For the equation of state of the neutron star matter, we use a relativistic mean field model for the hadronic one and the (axial‐)vector meson extended linear sigma model for the quark phase. We assume that the transition is a cross‐over between these phases. We connect the two branches in this cross‐over regime continuously by a polynomial. This equation of state should comply with the restrictions imposed by current astrophysical observations on compact stars. Our model has four free parameters that should be fitted to experimental data. By using a Bayesian analysis, we found that our model could explain all the experimental constraints; furthermore, we have obtained the most probable parameter set for our model.

Hybrid stars within the framework of the Sigma-Omega-Rho model combined with the MIT and NJL models

In this paper, we investigate the structure of hybrid stars consisting of hadrons (neutrons, protons, sigmas, lambdas), leptons (electrons, muons), and quarks (up, down, strange). We use a relativistic mean-field (RMF) model namely the Sigma-omega-rho model for the hadronic phase and the MIT bag model as well as the NJL model for the quark phase. In addition, Maxwell and Gibbs conditions are employed to investigate the hadron-Quark phase transition. Finally, by obtaining the mass-radius relation, M(Msun)⩽2.07 is predicted for such hybrid stars.

Observational constraint from the heaviest pulsar PSR J0952-0607 on the equation of state of dense matter in relativistic mean field model

In the present work, we constrain the equation of state of dense matter in the context of heaviest observed neutron-star mass ${M}_{\mathrm{max}}=(2.35\ifmmode\pm\else\textpm\fi{}0.17){M}_{\ensuremath{\bigodot}}$ for the black widow pulsar PSR J0952-0607. We propose three interactions HPU1, HPU2 and HPU3 (named after Himachal Pradesh University) for the relativistic mean-field model, which include different combinations of nonlinear, self-couplings, and cross couplings among isoscalar-scalar $\ensuremath{\sigma}$, and isoscalar-vector $\ensuremath{\omega}$ and isovector-vector $\ensuremath{\rho}$ meson fields up to the quartic order. These interactions are in harmony with the finite nuclei and bulk nuclear matter properties. The equations of state computed by using newly generated interactions for the $\ensuremath{\beta}$-equilibrated nucleonic matter satisfy the heaviest observed neutron-star mass ${M}_{\mathrm{max}}=(2.35\ifmmode\pm\else\textpm\fi{}0.17){M}_{\ensuremath{\bigodot}}$ for the black widow pulsar PSR J0952-0607. The results for the radius ${R}_{1.4}$ and dimensionless tidal deformability ${\mathrm{\ensuremath{\Lambda}}}_{1.4}$ corresponding to the canonical mass are also presented and agree well with the GW170817 event and astrophysical observations. The radius of $2.08{M}_{\ensuremath{\bigodot}}$ neutron-star mass is predicted to be in the range ${R}_{2.08}=12.98$--13.09 km which also satisfy the NICER observations by Miller et al. [Astrophys. J. Lett. 918, L28 (2021)] and Riley et al. [Astrophys. J. Lett. 918, L27 (2021)]. A covariance analysis is also performed to assess the theoretical uncertainties of model parameters and to determine their correlations with nuclear matter observables.

Neutron Stars in the Context of f(T,T) Gravity

In this work, we investigate the existence of neutron stars (NS) in the framework of f(T,T) gravity, where T is the torsion tensor and T is the trace of the energy–momentum tensor. The hydrostatic equilibrium equations are obtained, however, with p and ρ quantities passed on by effective quantities p¯ and ρ¯, whose mass–radius diagrams are obtained using modern equations of state (EoS) of nuclear matter derived from relativistic mean field models and compared with the ones computed by the Tolman–Oppenheimer–Volkoff (TOV) equations. Substantial changes in the mass–radius profiles of NS are obtained even for small changes in the free parameter of this modified theory. The results indicate that the use of f(T,T) gravity in the study of NS provides good results for the masses and radii of some important astrophysical objects, as, for example, the NS of low-mass X-ray binary in NGC 6397, the millisecond pulsar PSR J0740+6620 and the GW170817 event. In addition, radii results inferred from the Lead Radius Experiment (PREX-2) can also be described for certain parameter values.

Theoretical studies on structural properties and decay modes of $$^{284-375}$$119 isotopes

Within the axially deformed relativistic mean field with $$\hbox {NL3}^*$$ parametrisation, the different bulk properties like binding energy, quadrupole deformation parameter, separation energies, density profile and shape co-existence for Z = 119 isotopic chain within the mass range 284 $$\le$$ A $$\le$$ 375 are computed. Further, a competition between possible decay modes such as α-decay, $$\beta$$ -decay and spontaneous fission (SF) of the isotopic chain of Z = 119 superheavy nuclei under study is systematically analysed within self-consistent relativistic mean field model and a close agreement is noticed among the calculations performed using various semi-empirical formulae and also with the estimations made by finite range droplet model (FRDM) wherever available. Our analysis confirmed that α–decay is restricted within the mass range 284 $$\le$$ A $$\le$$ 375 and thus being the dominant decay channel in this mass range and there is no possibility of $$\beta$$ –decay for the considered isotopic chain. In addition, we forecasted the α–decay chain of fission survival nuclides, i.e. $$^{284-296}119$$ and found as one α chain from $$^{284} 119$$ and $$^{296} 119$$ , $$2 \alpha$$ chains from $$^{285}119$$ and $$^{295} 119$$ consistently, $$3\alpha$$ chains from $$^{286} 119$$ and $$^{294} 119$$ consistently, $$4 \alpha$$ chains from $$^{287} 119$$ consistently, six consistent α chains from $$^{288-293} 119$$ . A comparative study of SF and α-decay half-live computed using the formula of Santhosh et al and Coulomb proximity potential model (CPPM), respectively, for the fission surviving isotopic chain reveals that isotopes $$^{288-293} 119$$ exhibit $$6\alpha$$ chains followed by SF, isotopes $$^{295,296} 119$$ exhibit $$4\alpha$$ chains followed by SF, and the rest of the nuclei show continuous α chains. This study has also established that the alpha half-life values computed using $$\hbox {Q}_\alpha$$ (RMF) agree with half-life values computed using experimental $$\hbox {Q}_\alpha$$ values within 1 order difference. Thus, such studies can be of great significance to the experimentalists in very near future for synthesizing the isotopes of Z = 119 superheavy nuclei.

Comparative study on charge radii and their kinks at magic numbers

Isotope dependences of charge radii, i.e., isotope shifts, calculated by the Skyrme Hartree-Fock, the relativistic mean-field, and the relativistic Hartree-Fock calculations are compared against the experimental data of magic and semimagic nuclei. It is found that the tensor interaction plays a role in reproducing the ``kink'' behavior, irregularity of isotope shifts at the neutron magic number, in the relativistic Hartree-Fock approach. With several Skyrme models, it is found that the kink behavior can be reproduced with the spin-orbit interaction having nonzero isovector channel. The single-particle orbitals near the Fermi energy are crucial to determine the kink size. The effects of the symmetry energy and the pairing interaction are also discussed in relation to the kink behavior.

Bayesian inference of neutron-star observables based on effective nuclear interactions

Based on the Skyrme-Hartree-Fock model (SHF) as well as its extension [the Korea-IBS-Daegu-SKKU (KIDS) model] and the relativistic mean-field (RMF) model, we have studied the constraints on the parameters of the nuclear matter equation of state (EOS) from adopted astrophysical observables using a Bayesian approach. While the masses and radii of neutron stars generally favor a stiff isoscalar EOS and a moderately soft nuclear symmetry energy, model dependence on the constraints is observed and mostly originates from the incorporation of higher-order EOS parameters and differences between relativistic and nonrelativistic models. At twice saturation density, the value of the symmetry energy is constrained to be ${48}_{\ensuremath{-}11}^{+15}\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ in the standard SHF model, ${48}_{\ensuremath{-}15}^{+8}\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ in the KIDS model, and ${48}_{\ensuremath{-}6}^{+5}\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ in the RMF model, around their maximum a posteriori values within $68%$ confidence intervals. Our study helps to obtain a robust constraint on nuclear matter EOS, and, meanwhile, to understand the model dependence of the results.

Ground state and fission properties of even-A uranium isotopes from multidimensionally-constrained relativistic mean field model

The multidimensionally-constrained covariant density functional theories (MDC-CDFTs) have been developed to study the influence of octupole and triaxial deformations on the ground state and fission properties. In this paper, we present a brief review of the applications of MDC-CDFTs and discuss the results of a systematical study of even-[Formula: see text] uranium isotopes with the multidimensionally-constrained relativistic mean field (MDC-RMF) model which is one of the MDC-CDFTs with pairing correlations treated by using the Bardeen-Cooper-Schrieffer (BCS) approach. We examine in detail the two-dimensional potential energy surfaces [Formula: see text] of these U isotopes and discuss the ground state and fission properties as well as the third and fourth minima on the potential energy surfaces. The emphasis is put on the effects of octupole and triaxial deformations.

Stability of neutron stars with dark matter core using three crustal types and the impact on mass–radius relations

We investigate the effects of dark matter (DM) on the nuclear equation of state (EoS) and neutron star structure, in the relativistic mean field theory, both in the absence and presence of a crust. The σ−ω model is modified by adding a WIMP-DM component, which interacts with nucleonic matter through the Higgs portal. This model agrees well with previous studies which utilized either a more complicated nuclear model or higher-order terms of the Higgs potential, in that DM softens the EoS, resulting in stars with lower maximum masses. However, instabilities corresponding to negative pressure values in the low-energy density regime of the DM-admixed EoS are present, and this effect becomes more prominent as we increase the DM Fermi momentum. We resolve this by confining DM in the star’s core. The regions of instability were replaced by three types of crust: first by the Friedman-Pandharipande-Skyrme (FPS), Skyrme-Lyon (SLy) and BSk19 EoS from the Brussels-Montreal Group, which can be represented by analytical approximations. For a fixed value of the DM Fermi momentum pFDM, the DM-admixed neutron star does not have significant changes in its mass with the addition of the crusts. However, the entire mass–radius relation of the neutron star is significantly affected, with an observed increase in the radius of the star corresponding to the mass. The effect of DM is to reduce the mass of the star, while the crust does not affect the radius significantly, as the value of the pFDM increases.