Relativistic Mean Field Research Articles

Neutron capture on $$^{16}$$O within the framework of RMF + ACCC + BCS for astrophysical simulations

Neutron capture on $$^{16}$$ O may serve as a neutron poison in certain nucleosynthesis scenarios. We revisit this reaction at energy ranges of astrophysical interest, employing a novel theoretical approach that self-consistently treats capture through bound and resonant levels. Our covariant density functional theory is based on a relativistic mean field (RMF) theory with contributions from resonant orbitals included via the analytical continuation of the coupling constant (ACCC), and pairing correlations included via the resonant Bardeen–Cooper–Schrieffer (BCS) technique. We employ this RMF + ACCC + BCS approach to extract bound states, resonant states, and pairing correlations in $$^{17}$$ O in a self-consistent microscopic way. We calculate $$^{16}$$ O(n, $$\gamma $$ ) $$^{17}$$ O direct capture cross sections resulting from neutron E1 transitions from scattering states to bound states, resonant cross sections from a Breit–Wigner formalism, and Maxwellian-averaged cross sections and thermonuclear reaction rates for astrophysical applications. We use different effective interactions to determine the viability of our approach to determine the $$^{17}$$ O level structure and corresponding reaction rates. Comparisons to measurements and database values are given.

Equation-of-state Table with Hyperon and Antikaon for Supernova and Neutron Star Merger

Abstract We develop a new equation-of-state (EOS) table involving thermal (anti)kaons, Bose–Einstein condensate of K − mesons, and Λ-hyperons for core-collapse supernova and neutron star merger simulations. This EOS table is based on a finite-temperature, density-dependent relativistic hadron field theory where baryon–baryon interaction is mediated by scalar σ, vector ω, and ρ mesons, using the parameter set DD2 for nucleons. The repulsive hyperon–hyperon interaction is mediated by an additional strange ϕ meson. The EOS for the K − condensed matter is also calculated within the framework of the relativistic mean field model, whereas the low-density, inhomogeneous matter is calculated in the extended nuclear statistical equilibrium model. The EOS table is generated for a wide range of values of three parameters—baryon density (10−12 to ∼1 fm−3), positive charge fraction (0.01–0.60), and temperature (0.1–158.48 MeV).

Supermassive neutron stars rule out twin stars

We investigate the implications of a hypothetical $2.5\text{ }\text{ }{\mathrm{M}}_{\ensuremath{\bigodot}}$ neutron star in regard to the possibility of a first order phase transition to quark matter. We use equations of state (EoS) of varying stiffness provided by a parametrizable relativistic mean field model transitioning to a constant speed of sound EoS. We find a strong connection between the discontinuity in energy density and the maximal neutron star mass. We demonstrate, that high maximal masses cannot be realized for large discontinuities. As a result visible mass gaps, i.e., twin stars, and masses of ${M}_{\mathrm{max}}\ensuremath{\gtrsim}2.2\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ are mutually exclusive.

Effect of inner crust EoS on neutron star properties

The neutron star maximum mass and the radius are investigated within the framework of the relativistic mean-field (RMF) model. The variation in the radius at the canonical mass, R1.4, using different inner crust equation of state (EoS) with different symmetry energy slope parameter is studied. It is found that although the NS maximum mass and the corresponding radius do not vary much with different inner crust EoSs, the radius and the tidal deformability at 1.4M⊙ vary with the different choice of crust EoS and variation of about 1-2 km is seen in the radius at the canonical mass. For non-unified EoSs, the crust with a low symmetry energy slope parameter produces a low NS radius at the canonical mass. The properties of maximally rotating neutron stars are also studied. The variation in the radius of rotating star at the canonical mass 1.4M⊙ is also seen with the slope parameter. Similar to the static neutron star, the radius at 1.4M⊙ of rotating neutron star is affected by slope parameter of the inner crust. Other important quantities like moment of inertia, frequency, rotational kinetic energy to gravitational energy ratio are also calculated. The variation in these quantities with the crust slope parameter is found to be more proportional to the mass and the radius of NS.

Towards a systematic optical model potential for A = 8 projectiles

An optical model analysis of the available data for A = 8 ( $$^8$$ He, $$^8$$ Li and $$^8$$ B) projectiles on different targets with light, medium and heavy mass has been performed. A systematic potential set based on a Woods–Saxon Potential shape was obtained. This potential describes the elastic scattering angular distributions quite well. A more physical model within the framework of a semi-microscopic approach, where the nuclear matter density distributions of the $$^8$$ B, $$^8$$ Li and $$^8$$ He projectiles have been calculated by using a microscopic self-consistent relativistic mean field (RMF) theory, was also considered. The agreement of the calculated angular distributions with the data was reasonable. An improvement of the agreement could be achieved by changing the imaginary diffuseness parameter, which is a sensitive parameter in these calculations.

A Modern View of the Equation of State in Nuclear and Neutron Star Matter

Background: We analyze several constraints on the nuclear equation of state (EOS) currently available from neutron star (NS) observations and laboratory experiments and study the existence of possible correlations among properties of nuclear matter at saturation density with NS observables. Methods: We use a set of different models that include several phenomenological EOSs based on Skyrme and relativistic mean field models as well as microscopic calculations based on different many-body approaches, i.e., the (Dirac–)Brueckner–Hartree–Fock theories, Quantum Monte Carlo techniques, and the variational method. Results: We find that almost all the models considered are compatible with the laboratory constraints of the nuclear matter properties as well as with the largest NS mass observed up to now, 2.14−0.09+0.10M⊙ for the object PSR J0740+6620, and with the upper limit of the maximum mass of about 2.3–2.5M⊙ deduced from the analysis of the GW170817 NS merger event. Conclusion: Our study shows that whereas no correlation exists between the tidal deformability and the value of the nuclear symmetry energy at saturation for any value of the NS mass, very weak correlations seem to exist with the derivative of the nuclear symmetry energy and with the nuclear incompressibility.

Momentum dependent mean-fields of (anti)hyperons

We investigate the in-medium properties of hyperons and anti-hyperons in the framework of the Non-Linear Derivative (NLD) model. We focus on the momentum dependence of in-medium strangeness optical potentials. The NLD model is based on the simplicity of the well-established Relativistic Mean-Field (RMF) approximation, but it incorporates an explicit momentum dependence on a field-theoretical level. The extension of the NLD model to the (anti)baryon-octet is formulated in the spirit of SU(6) and G-parity arguments. It is shown that with an appropriate choice of momentum cut-offs the Λ, Σ and Ξ optical potentials are consistent with recent studies of the chiral effective field theory and Lattice-QCD calculations over a wide momentum region. In addition, we present NLD predictions for the in-medium momentum dependence of Λ‾-, Σ‾- and Ξ‾-hyperons. This work is important for future experimental studies such as CBM, PANDA at the Facility for Antiproton and Ion Research (FAIR). It is relevant for nuclear astrophysics too.

Application of the coherent density fluctuation model to study the nuclear matter properties of finite nuclei within the relativistic mean-field formalism

We obtained a density-dependent analytical expression of binding energy per nucleon for different neutron-proton asymmetry of the nuclear matter (NM) with a polynomial fitting, which manifests the results of effective field theory motivated relativistic mean-field (E-RMF) model. This expression has the edge over the Br$\ddot{u}$ckner energy density functional [Phys. Rev. {\bf 171}, 1188 (1968)] since it resolves the Coster-Band problem. The NM parameters like incompressibility, neutron pressure, symmetry energy, and its derivatives are calculated using the acquired expression of energy per nucleon. Further, the weight function calculated by E-RMF densities are folded with calculated NM parameters within coherent density fluctuation model to find the properties of closed/semi-closed-shell even-even $^{16}$O, $^{40}$Ca, $^{48}$Ca, $^{56}$Ni, $^{90}$Zr, $^{116}$Sn, and $^{208}$Pb nuclei. The values obtained for the neutron pressure $P^{A}$, symmetry energy $S^{A}$ and its derivative $L_{sym}^A$ known as slope parameter, lie within a narrow domain whereas there is a large variation in isoscalar incompressibility $K^{A}$ and surface incompressibility $K_{sym}^{A}$ while moving from light to heavy nuclei. The sizable variation in $K^{A}$ and $K_{sym}^{A}$ for light and heavy nuclei depicts their structural dependence due to the peculiar density distribution of each nucleus. A comparison of surface quantities calculated in the present work has also been made with ones obtained via Br$\ddot{u}$ckner energy density functional.

Hadron–Quark Phase Transition in the SU (3) Local Nambu–Jona-Lasinio (NJL) Model with Vector Interaction

We study the hadron–quark hybrid equation of state (EOS) of compact-star matter. The Nambu–Jona-Lasinio (NJL) local SU (3) model with vector-type interaction is used to describe the quark matter phase, while the relativistic mean field (RMF) theory with the scalar-isovector δ-meson effective field is adopted to describe the hadronic matter phase. It is shown that the larger the vector coupling constant GV, the lower the threshold density for the appearance of strange quarks. For a sufficiently small value of the vector coupling constant, the functions of the mass dependence on the baryonic chemical potential have regions of ambiguity that lead to a phase transition in nonstrange quark matter with an abrupt change in the baryon number density. We show that within the framework of the NJL model, the hypothesis on the absolute stability of strange quark matter is not realized. In order to describe the phase transition from hadronic matter to quark matter, Maxwell’s construction is applied. It is shown that the greater the vector coupling, the greater the stiffness of the EOS for quark matter and the phase transition pressure. Our results indicate that the infinitesimal core of the quark phase, formed in the center of the neutron star, is stable.

Critical properties of symmetric nuclear matter in low-density regime using effective-relativistic mean field formalism

The effective field theory motivated relativistic mean-field (E-RMF) formalism is employed to study the equation of state (EoS) for the infinite symmetric nuclear matter (SNM) at finite temperature using the recently developed forces FSUGarnet, IOPB-I, G3, and the well known NL3 force parameter. The EoS is then used to estimate the critical temperature T c, pressure P c and density ρ c of the SNM for the liquid–gas phase transition. As T c is not a constrained parameter in both experiments and theoretical calculations, there is a large uncertainty around its value. Although, the critical parameters are correlated among themselves. It is revealed that vector self-coupling ζ 0 of used forces play determining role in EoS in finite temperature limit. Keeping the incompressibility in acceptable limit i.e. 240 ± 20 MeV, the lower value of ζ 0 gives a better result of T c when compared to the several experimental data. The critical parameters however show weak correlation with the properties at saturation density at zero temperature. The compressibility factors calculated with these parameters are in agreement with the universal value of liquid–gas systems. Stability conditions are examined along with binodal and spinodal regions. Besides this, the thermodynamic properties like specific heat and latent heat are also worked out. We have carried out detailed consistency check of our calculations using critical exponents and standard scaling laws. All the exponents are well within the theoretical mean-field results.

Impact of strong magnetic fields on the inner crust of neutron stars

We study the impact of strong magnetic fields on the pasta phases that are expected to exist in the inner crust of neutron stars. We employ the relativistic mean field model to describe the nucleon interaction and use the self-consistent Thomas-Fermi approximation to calculate the nonuniform matter in neutron star crust. The properties of pasta phases and crust-core transition are examined. It is found that as the magnetic field strength $B$ is less than ${10}^{17}$ G, the effects of magnetic field are not evident comparing with the results without magnetic field. As $B$ is stronger than ${10}^{18}$ G, the onset densities of pasta phases and crust-core transition density decrease significantly, and the density distributions of nucleons and electrons are also changed obviously.

Momentum dependent mean-fields of hyperons & antihyperons

The in-medium properties of hyperons and antihyperons are studied with the Non-Linear Derivative (NLD) model and focus is made on the momentum dependence of strangeness optical potentials. The NLD model is based on the Relativistic Mean Field (RMF) approximation to Relativistic Hadrodynamics (RHD) approach of nuclear systems, but it incorporates an explicit momentum dependence of mean-fields. The extension of the NLD model to the baryon and antibaryon octet is based on SU(6) and G-parity arguments. It is demonstrated that with a proper choice of momentum cut-offs, the Λ and Σ optical potentials are consistent with recent studies of the chiral effective field theory(χ -EFT) and optical potentials are consistent with Lattice-QCD calculations, over a wide momentum region. We also present NLD predictions for the in-medium momentum dependence of ∧¯, ∑¯ and Ξ¯ hyperons. This work is important for future experimental studies, like CBM, PANDA at FAIR and is relevant to nuclear astrophysics as well.

Discontinuity g‐modes of hybrid stars: Effect of sequential phase transitions

AbstractThe detection of event GW170817 and its electromagnetic counterpart started the era of multi‐messenger astronomy with gravitational waves. The observational constraints from this event and the estimation of mass and radius of PSR J0030 + 0451 is being used to get insights related to the nature of matter inside these compact objects. In this work, we construct hybrid equations of state using modern parametrizations of the relativistic mean field model for the outer core and a generalization of the Constant Speed of Sound parametrization that allow to study sharp sequential phase transitions in the inner core. Moreover, we study non‐radial perturbations of these stellar configurations using the relativistic Cowling approximation. We focus our attention on the g‐modes that arise due to the sharp phase transitions and show that, due to the second phase transition, a new g‐mode appears, g2‐mode, with frequencies smaller that ∼0.5 kHz.

Effects of strong magnetic field on moment of inertia and surface gravitational redshift in neutron star

Research on the properties of neutron stars with strong magnetic fields is of great significance in constraining the equation of state and revealing the real distribution of magnetic fields in neutron stars. The main macroscopic properties of the traditional neutron star matter under <i>β</i> equilibrium condition are studied within the relativistic mean field theory through using the GL91 parameter set by considering the strong magnetic field. It is found that the onset of the strong magnetic field leads to the stiffened equation of state of the traditional neutron star matter. The maximum mass of the traditional neutron star grows from 2.111 M<sub>⊙</sub> to 3.081 M<sub>⊙</sub>, the radius of the fixed mass traditional neutron star grows larger with the increase of internal magnetic field, which makes traditional neutron star become less dense. The strong magnetic field can also reduce the surface gravitational redshift and strengthen the moment of inertia of the traditional neutron star matter. In addition, the theoretical ranges of the surface gravitational redshift and the moment of inertia for the four massive PSRs J1614-2230, J0348+0432, J0740+6620 and J2215-5135, and the 2.50 M<sub>⊙</sub> − 2.67 M<sub>⊙</sub> compact object in the binary merger event GW190814 are also given. The results show that the ranges of the surface redshift become narrower, while the scopes of the moment of inertia widen as the magnetizing field increases in the five stars.

Calculations of the Alpha Decay Half-lives of Some Polonium Isotopes Using the Double Folding Model

The calculations of the alpha decay half-lives of some Polonium isotopes in the mass range 186 - 218 have been carried out using the Wentzel-Kramers-Brillouin (WKB) semiclassical approximation. The alpha-nucleus effective potential used contains the Coulomb potential, centrifugal potential, and the nuclear potential. The nuclear potential is obtained via the double folding model, with the microscopic NN effective interactions derived from relativistic mean field theory Lagrangian (termed R3Y). Different parametrizations of the R3Y interactions have been employed in the computation of the nuclear potentials. The results obtained using the R3Y NN interactions are compared with the ones obtained using the famous Michigan-3-Yukawa (M3Y) interactions. The use of density-dependent NN interaction is also considered. When compared to available experimental data, there are improvements in the results when density-dependent interaction potentials are used compared to when density-independent interactions are employed.

Magnetized rotational neutron star and the MR relations

Radii and masses of neutron stars are calculated for various EoSs using a perturbative approach. Also increased masses are calculated due to magnetic fields. Moreover, the radius of a neutron star is calculated as a function of its increased total mass by rotation. As for the EoSs, we adopt 5 hadronic EoSs in relativistic mean field (RMF) theory to calculate the mass-radius relations (MR relations). It is found that the total masses are over twice the solar mass for all 5 hadronic EoSs in the presence of magnetic fields together with rotation. Three obtained EoSs (GM1, TM2-ωρ-a and TM2-ωρ-b) are found to be in the range of the observation. Hybrid stars are calculated to have masses more than twice the solar mass in a rapid rotation for 5 EoSs.

Role of antikaon condensation on the universality relations of hot and rapidly rotating neutron stars

We study cold as well as hot neutron star (NS) at finite entropy using density dependent relativistic mean field model in the presence of nucleons and antikaon condensates. The parameters like gravitational mass(M), radius(R), moment of inertia(I) and quadrupole moment(Q) are calculated as a function of rotation frequency for a NS with fixed baryonic mass. Next, we investigate the relation of normalized I with compactness (M/R). Finally, we extend our study to calculate the tidal deformability parameter and tidal love number and show their variation with compactness.

Detail study of application of the relativistic mean-field effective NN forces for heavy-ion fusion within a dynamical model

In the analysis of the heavy-ion above-barrier fusion cross-sections of complex nuclei, the relativistic effects are usually ignored. In the present work, we undertake a step toward accounting for these effects. Namely, the nucleus–nucleus interaction potential is obtained using the double-folding model with six different effective nucleon–nucleon (NN) forces coming from the relativistic mean field (RMF) theory. We also compare our present results with the ones obtained with the non-relativistic M3Y NN-forces. In all calculations, the nuclear densities resulting from the Hartree–Fock approach with the SKX-Skyrme forces accounting for the tensor part are used. Our calculations show that four sets of the considered RMF forces cannot be used for describing heavy ion fusion. Of the remaining two sets, one results in the barriers which are too high not leaving any room for the dissipative effects. Only the potentials calculated using the NL2 NN-forces allow us to reproduce the experimental cross-sections within the framework of the fluctuation–dissipation trajectory model with surface friction with a typical accuracy of 3%–5%. The values of the variable parameter of the model which defines the friction strength resulting from the present calculations are systematically lower than those obtained earlier with the M3Y NN-forces.

Skyrme-Hartree-Fock-Bogoliubov Calculations of Neutron Density Distributions of Mg Isotopes

There are several important open questions that need to be addressed by exploring the nuclear landscape of the nuclei properties. The physics of rich neutron nuclei is one of the most subjects in nuclear structure physics both theoretically and experimentally. The Hartree-Fock-Bogolyubov (HFB) theory is a good theoretical framework for describing the nuclear structure of nuclei. Using HFB method with four different Skyrme types effective nucleon-nucleon interactions: SIII, SKM*, SLy4 and UNE0. The ground-state properties of even-even neutron-rich Mg isotopes have been investigated. Having different types of Skyrme-force parameterizations requires a continuous search for the best for describing the experimental data. Our results of protons and neutrons rms radii, neutrons skin thickness and neutrons density distributions have been compared with the available data of Hartree-Fock-Bogoliubov calculations based on the D1S Gogny interaction, and predictions of some nuclear theories such as Relativistic Mean Field (RMF) theory. Our investigated Skyrme functionals show good agreements in comparison with other data and results.

Possible Candidates for Chirality in the Odd-Odd As IsotopesSupported by the National Natural Science Foundation of China (Grant Nos. 11705102 and 11675094), the Shandong Natural Science Foundation (Grant No. JQ201701), and the Young Scholars Program of Shandong University, Weihai.

The deformations and the corresponding configurations of the odd-odd As isotopes are investigated using the adiabatic and configuration-fixed constrained triaxial relativistic mean field (RMF) theory. Energy minima with triaxial deformations and high-j particle-hole configurations are obtained in 72,74,76,78,80As, where the chiral doublet bands are possible to appear. The existence of multiple chiral doublet (MχD) is demonstrated in 74,76,78As. Based on the calculated single-particle levels, we also find possible coexistence of chiral and pseudospin symmetries in the odd-odd As isotopes.