Nuclear Theory·nucl-th

Tuesday·September 7, 2021

15 papers—11 primary·4 cross-listed

01
[Submitted on 3 Sept 2021]
Vector interactions inhibit quark-hadron mixed phases in neutron stars
G. Lugones🇧🇷 · A. G. Grunfeld🇦🇷
We investigate the surface tension $σ$ and the curvature energy $γ$ of quark matter drops in the MIT bag model with vector interactions. Finite size corrections to the density of states are implemented by using the multiple reflection expansion (MRE) formalism. We find that $σ$ and $γ$ are strongly enhanced by new terms arising from vector interactions. With respect to the noninteracting case they are increased by a large factor, which can be as high as $\sim 10$ when the vector coupling constant $g$ varies within the range used in the literature. This behavior may have major consequences for the hadron-quark mixed phase speculated to exist at neutron star (NS) interiors, which may be totally suppressed or have its extension substantially reduced.
Comments:
6 pages, 2 figures, to appear in Physical Review D Letters
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2109.01749 [pdf]
PRD(2021)·31 citations
02
[Submitted on 4 Sept 2021]
Shell-structure and asymmetry effects in level densities
A.G. Magner · A.I. Sanzhur · S.N. Fedotkin · A.I. Levon · S. Shlomo
Level density $ρ (E, N, Z)$ is derived for a nuclear system with a given energy $E$ , neutron $N$ , and proton $Z$ particle numbers, within the semiclassical extended Thomas-Fermi and periodic-orbit theory beyond the Fermi-gas saddle-point method. We obtain $ρ \propto I_{ν} (S) / S^{ν}$ ,~~ where $I_{ν} (S)$ is the modified Bessel function of the entropy $S$ , and $ν$ is related to the number of integrals of motion, except for the energy $E$ . For small shell structure contribution one obtains within the micro-macroscopic approximation (MMA) the value of $ν = 2$ for $ρ (E, N, Z)$ . In the opposite case of much larger shell structure contributions one finds a larger value of $ν = 3$ . The MMA level density $ρ$ reaches the well-known Fermi gas asymptote for large excitation energies, and the finite micro-canonical limit for low excitation energies. Fitting the MMA $ρ (E, N, Z)$ to experimental data on a long isotope chain for low excitation energies, due mainly to the shell effects, one obtains results for the inverse level density parameter $K$ , which differs significantly from that of neutron resonances.
Comments:
26 pages, 3 figures, 1 table. arXiv admin note: text overlap with arXiv:2103.16480
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2109.01830 [pdf]
IJMPE(2021)·5 citations
03
[Submitted on 4 Sept 2021]
Impacts of dark matter on the $f$ -mode oscillation of hyperon star
H. C. Das🇮🇳 · Ankit Kumar🇮🇳 · S. K. Biswal🇮🇳 · S. K. Patra🇮🇳
We investigate the $f$ -mode oscillation of the dark matter admixed hyperon star within the relativistic Cowling approximation. The macroscopic properties are calculated with the relativistic mean-field equation of states by assuming that the dark matter particles are inside the star. The $f$ -mode oscillation frequencies (only for $l = 2$ ) are calculated with four different neutron star equation of states. We also check the effects of hyperons/dark matter and hyperons with dark matter equation of states on the $f$ -mode oscillations varying with different astrophysical quantities such as mass ( $M$ ), radius ( $R$ ), compactness ( $M / R$ ), surface red-shift ( $Z_{s}$ ), average density ( $ρ ˉ$ ), dimensionless tidal deformability ( $Λ$ ) of the neutron star. Significant changes have been seen in the $f$ -mode frequencies with and without hyperons/dark matter or hyperons+dark matter. Substantial correlations are observed between canonical frequencies and $Λ$ ( $f_{1.4} - Λ_{1.4}$ ) and maximum frequencies and canonical $Λ$ ( $f_{ma x} - Λ_{1.4}$ ).
Comments:
13 pages, 11 figures, 3 tables, Published in Physics. Rev. D
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
arXiv:
2109.01851 [pdf]
PRD(2021)·67 citations
04
[Submitted on 4 Sept 2021]
Equation of state and composition of proto-neutron stars and merger remnants with hyperons
Armen Sedrakian🇩🇪 · Arus Harutyunyan🇦🇲
Finite-temperature equation of state (EoS) and the composition of dense nuclear and hypernuclear matter under conditions characteristic of neutron star binary merger remnants and supernovas are discussed. We consider both neutrino free-streaming and trapped regimes which are separated by a temperature of a few MeV. The formalism is based on covariant density functional (CDF) theory for the full baryon octet with density-dependent couplings, suitably adjusted in the hypernuclear sector. The softening of the EoS with the introduction of the hyperons is quantified under various conditions of lepton fractions and temperatures. We find that $Λ$ , $Ξ^{-}$ , and $Ξ^{0}$ hyperons appear in the given order with a sharp density increase at zero temperature at the threshold being replaced by an extended increment over a wide density range at high temperatures. The $Λ$ hyperon survives in the deep subnuclear regime. The triplet of $Σ$ s is suppressed in cold hypernuclear matter up to around seven times the nuclear saturation density, but appears in significant fractions at higher temperatures, $T \geq 20$ MeV, in both supernova and merger remnant matter. We point out that a special isospin degeneracy point exists where the baryon abundances within each of the three isospin multiplets are equal to each other as a result of (approximate) isospin symmetry. At that point, the charge chemical potential of the system vanishes. We find that under the merger remnant conditions, the fractions of electron and $μ$ -on neutrinos are close and are about 1\%, whereas in the supernova case, we only find a significant fraction ( $\sim$ 10\%) of electron neutrinos, given that in this case, the $μ$ -on lepton number is zero.
Comments:
v2: 16 pages, 7 figure, minor clarifications, matches published version. v1: 17 pages, 6 figures, submitted to "Universe"
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2109.01919 [pdf]
Universe(2021)·23 citations
05
[Submitted on 5 Sept 2021]
An overview of symmetric nuclear matter properties from chiral interactions up to fourth order of the chiral expansion
Francesca Sammarruca🇺🇸 · Randy Millerson🇺🇸
We present and discuss predictions for a cross section of bulk and single-particle properties in symmetric nuclear matter based on recent high-quality nucleon-nucleon potentials at N3LO and including all subleading three-nucleon forces. We begin with the equation of state and its saturation properties and proceed to the single-nucleon potential. We also explore short-range correlations as seen through the defect function. The various predictions which we present have a common foundation in an internally consistent ab initio approach.
Comments:
arXiv admin note: text overlap with arXiv:1807.06640
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2109.01985 [pdf]
PRC(2021)·24 citations
06
[Submitted on 6 Sept 2021]
Tensor force role in $β$ decays analyzed within the Gogny-interaction shell model
B. Dai🇨🇳 · B. S. Hu🇨🇳 · Y. Z. Ma🇨🇳 · J. G. Li🇨🇳 · S. M. Wang🇨🇳 · C. W. Johnson🇺🇸 · F. R. Xu🇨🇳
Background: The half-life of the famous $^{14}$ C $β$ decay is anomalously long, with different mechanisms: the tensor force, cross-shell mixing, and three-body forces, proposed to explain the cancellations that lead to a small transition matrix element. Purpose: We revisit and analyze the role of the tensor force for the $β$ decay of $^{14}$ C as well as of neighboring isotopes. Methods: We add a tensor force to the Gogny interaction, and derive an effective Hamiltonian for shell-model calculations. The calculations were carried out in a $p$ - $s d$ model space to investigate cross-shell effects. Furthermore, we decompose the wave functions according to the total orbital angular momentum $L$ in order to analyze the effects of the tensor force and cross-shell mixing. Results: The inclusion of the tensor force significantly improves the shell-model calculations of the $β$ -decay properties of carbon isotopes. In particular, the anomalously slow $β$ decay of $^{14}$ C can be explained by the isospin $T = 0$ part of the tensor force, which changes the components of $^{14}$ N with the orbital angular momentum $L = 0, 1$ , and results in a dramatic suppression of the Gamow-Teller transition strength. At the same time, the description of other nearby $β$ decays are improved. Conclusions: Decomposition of wave function into $L$ components illuminates how the tensor force modifies nuclear wave functions, in particular suppression of $β$ -decay matrix elements. Cross-shell mixing also has a visible impact on the $β$ -decay strength. Inclusion of the tensor force does not seem to significantly change, however, binding energies of the nuclei within the phenomenological interaction.
Comments:
8 Pages,7 Figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2109.02205 [pdf]
PRC(2021)·7 citations
07
[Submitted on 6 Sept 2021]
First application of dispersive optical model to ( $p$ , $2 p$ ) analysis within distorted wave impulse approximation framework
K. Yoshida · M. C. Atkinson · K. Ogata · W. H. Dickhoff
Both ( $e$ , $e^{'} p$ ) and ( $p$ , $2 p$ ) reactions have been performed to study the proton single-particle character of nuclear states with its related spectroscopic factor. Recently, the dispersive optical model (DOM) was applied to the ( $e$ , $e^{'} p$ ) analysis revealing that the traditional treatment of the single-particle overlap function, distorted waves, and nonlocality must be further improved to achieve quantitative nuclear spectroscopy. We apply the DOM wave functions to the traditional ( $p$ , $2 p$ ) analysis and investigate the consistency of the DOM spectroscopic factor that describes the ( $e$ , $e^{'} p$ ) cross section with the result of the ( $p$ , $2 p$ ) analysis. Additionally, we make a comparison with a phenomenological single-particle wave function and optical potential. Uncertainty arising from a choice of $p$ - $p$ interaction is also investigated. We implement the DOM wave functions to the distorted wave impulse approximation (DWIA) framework for ( $p$ , $2 p$ ) reactions. DOM + DWIA analysis on $^{40}$ Ca( $p$ , $2 p$ ) $^{39}$ K data generates a proton $0 d_{3/2}$ spectroscopic factor of 0.560, which is meaningfully smaller than the DOM value of 0.71 shown to be consistent with the ( $e$ , $e^{'} p$ ) analysis. Uncertainties arising from choices of single-particle wave function, optical potential, and $p$ - $p$ interaction do not explain this inconsistency. The inconsistency in the spectroscopic factor suggests there is urgent need for improving the description of $p$ - $p$ scattering in a nucleus and the resulting in-medium interaction with corresponding implications for the analysis of this reaction in inverse kinematics.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2109.02211 [pdf]
PRC(2022)·3 citations
08
[Submitted on 6 Sept 2021]
Collapse of N $=$ 28 magicity in exotic $^{40}$ Mg -- Probe of deformed halo and 2n-radioactivity at Mg neutron drip-line
G. Saxena · M. Kumawat · R. Sharma · Mamta Aggarwal
The exotic phenomenon of two-neutron halos and 2n-radioactivity are explored in the neutron-rich $^{40, 42, 44}$ Mg by employing various variants of the relativistic mean-field approach. The extended tail of spatial density distributions including the enhanced neutron radii and skin thickness, pairing correlations, single-particle spectrum and wave functions predict $^{40, 42, 44}$ Mg to be strong candidates for deformed neutron halos. Weakening of magicity at N $=$ 28 plays a significant role in the existence of a weakly bound halo in $^{40}$ Mg which is currently the heaviest isotope of Mg accessible experimentally. Large deformation, mixing of f-p shell Nilsson orbitals and the valence neutron occupancy of p-states leads to a reduced centrifugal barrier and broader spatial density distributions that favour 2n-radioactivity in $^{42, 44}$ Mg.
Comments:
14 Pages, 7 Figures, Accepted in J Phys G: Nucl Part Phys
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2109.02326 [pdf]
J.Phys.G(2021)·5 citations
09
[Submitted on 6 Sept 2021]
Low-energy monopole strength in spherical and deformed nuclei : cluster and soft modes
F. Mercier🇫🇷 · J.-P. Ebran🇫🇷 · E. Khan🇫🇷
Background : Several recent experiments report significant low-energy isoscalar monopole strength, below the giant resonance, in various nuclei. In light $α$ -conjugate nuclei, these low-energy resonances were recently interpreted as cluster vibration modes. However, the nature of these excitations in neutron-rich nuclei remain elusive. Purpose : The present work provides a systematic analysis of the low-energy monopole strength in isotopic chains, from Neon to Germanium, in order to monitor and understand its nature and conditions of emergence. Methods : We perform covariant quasiparticle random phase approximation (QRPA) calculations, formulated within the finite amplitude method (FAM), on top of constrained relativistic Hartree-Bogoliubov (RHB) reference states. Results : Neutron excess leads to the appearance of low-energy excitations according to a systematic pattern reflecting the single-particle features of the underlying RHB reference state. With the onset of deformation, these low-energy resonances get split and give rise to more complex patterns, with possible mixing with the giant resonance. At lower energy, cluster-like excitations found in $N = Z$ systems survive in neutron-rich nuclei, with valence neutrons arranging in molecular-like orbitals. Finally, at very low energy, pair excitations are also found in superfluid nuclei, but remain negligible in most of the cases. Conclusions : The low-energy part of the monopole strength exhibits various modes, from cluster vibrations ( $\sim$ 5-10 MeV) to components of the giant resonance downshifted by the onset of deformation, including soft modes ( $\sim$ 10-15 MeV) as well as pair excitation ( $<$ 5 MeV), with possible mixing, depending on neutron-excess, deformation, and pairing energy.
Comments:
15 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2109.02498 [pdf]
PRC(2022)·5 citations
10
[Submitted on 6 Sept 2021]
Unified Equation of State for Neutron Stars Based on the Gogny Interaction
Xavier Viñas🇪🇸 · Claudia Gonzalez-Boquera🇪🇸 · Mario Centelles🇪🇸 · Chiranjib Mondal🇫🇷 · Luis M. Robledo🇪🇸
The most popular Gogny parametrizations, namely D1S, D1N and D1M, describe accurately the ground-state properties of spherical and deformed finite nuclei all across the mass table obtained with Hartree--Fock--Bogoliubov (HFB) calculations. However, these forces produce a rather soft equation of state (EoS) in neutron matter, which leads to predict maximum masses of neutron stars well below the observed value of two solar masses. To remove this limitation, we built new Gogny parametrizations by modifying the density dependence of the symmetry energy predicted by the force in such a way that they can be applied to the neutron star domain and can also reproduce the properties of finite nuclei as good as their predecessors. These new parametrizations allow us to obtain stiffer EoS's based on the Gogny interactions, which predict maximum masses of neutron stars around two solar masses. Moreover, other global properties of the star, such as the moment of inertia and the tidal deformability, are in harmony with those obtained with other well tested EoSs based on the SLy4 Skyrme force or the Barcelona--Catania--Paris--Madrid (BCPM) energy density functional. Properties of the core-crust transition predicted by these Gogny EoSs are also analyzed. Using these new Gogny forces, the EoS in the inner crust is obtained with the Wigner--Seitz approximation in the Variational Wigner--Kirkwood approach along with the Strutinsky integral method, which allows one to estimate in a perturbative way the proton shell and pairing corrections. For the outer crust, the EoS is determined basically by the nuclear masses, which are taken from the experiments, wherever they are available, or by HFB calculations performed with these new forces if the experimental masses are not known.
Comments:
31 pages, 13 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2109.02520 [pdf]
Symmetry(2021)·31 citations
11
[Submitted on 6 Sept 2021]
Deblurring for Nuclei: 3D Characteristics of Heavy-Ion Collisions
Pawel Danielewicz (FRIB-MSU)🇺🇸 · Mizuki Kurata-Nishimura (RIKEN)🇯🇵
Observables from nuclear and high-energy experiments can be degraded by detector performance and/or methodology in extracting the observables, such as of the final-state characteristics of heavy-ion collisions in relation to a coarsely estimated reaction-plane direction. We propose the use of deblurring methods, such as in optics, to correct for observable degradation. Our main focus is the restoration of triple-differential particle distributions in heavy-ion collisions. We demonstrate that these could be extracted from collision measurements following the Richardson-Lucy deblurring method from optics. We illustrate basic features of the restoration methodology in a schematic model assuming either ideal or more realistic particle detection. The inferred three-dimensional (3D) distributions for collisions may easier to interpret in terms of collision dynamics and sought properties of bulk matter than the currently employed Fourier coefficients, that combine information from different azimuthal angles relative to the reaction plane.
Comments:
17 pages,11 figures, 26 references
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2109.02626 [pdf]
PRC(2022)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE