Nuclear Theory·nucl-th

Tuesday·June 16, 2020

17 papers—10 primary·7 cross-listed

01
[Submitted on 12 Jun 2020]
Entanglement and correlation in two-nucleon systems
A T Kruppa · J Kovács · P Salamon · Ö Legeza
We examine the mode entanglement and correlation of two fermionic particles. We study the one- and two-mode entropy and a global characteristic, the one-body entanglement entropy. We consider not only angular momentum coupled states with single configuration but use the configuration interaction method. With the help of the Slater decomposition, we derive analytical expressions for the entanglement measures. We show that when the total angular momentum is zero specific single configurations describe maximally entangled states. It turns out that for a finite number of associated modes the one- and two-mode entropies have identical values. In the shell model framework, we numerically study two valence neutrons in the $s d$ shell. The one-body entanglement entropy of the ground state is close to the maximal value and the associated modes have the largest mutual information.
Comments:
20 pages, 1 figure
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el)
arXiv:
2006.07448 [pdf]
J.Phys.G(2021)·39 citations
02
[Submitted on 13 Jun 2020]
Least action and the maximum-coupling approximations in the theory of spontaneous fission
K. Hagino · G.F. Bertsch
We investigate the dynamics of spontaneous fission in a configuration-interaction (CI) approach. In that formalism the decay rate is governed by an effective interaction coupling the ground-state configuration and a fission doorway configuration, with the interaction strength determined by inverting a high-dimensioned CI Hamiltonian matrix that may have a block-tridiagonal structure. It is shown that the decay rate decreases exponentially with the number of blocks at a rate determined by the largest eigenvalue of a matrix in the block space for Hamiltonians with identical off-diagonal blocks. The theory is greatly simplified by approximations similar in spirit to the adiabatic and the least-action approximations in continuum representations. Here each block is replaced by a single matrix element. While the adiabatic reduction underestimates the coupling, a reduction based on a maximum-coupling approximation works well in a schematic CI model.
Comments:
9 pages, 5 figures. To appear in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.07524 [pdf]
PRC(2020)·6 citations
03
[Submitted on 13 Jun 2020]
Nuclear-Elastic Scattering of $^{9}$ Be+ $^{4}$ He using the Proximity Potential
Austin A. Morris
A nuclear-elastic $^{9}$ Be+ $^{4}$ He reaction is investigated. A tangential literature overview of the proximity potential is presented, necessitated by an approximate method for calculating $l -values$ . The model is surveyed intensively, from classical conception (liquid drop model) to physical implication (fusion barrier height), leading to a second-part calculation of the $^{9}$ Be+ $^{4}$ He angular distribution. The results obtained are limited by the exclusion of phase variation, but provide enough accuracy to give order-of-magnitude estimates for nuclei interacting peripherally, in agreement with experiment.
Comments:
18 pages
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.07679 [pdf]
0 citations
04
[Submitted on 14 Jun 2020]
Force and pressure in many-particle quantum dynamics
G.F. Bertsch
The Newtonian concept of force may be useful in some aspects of the dynamics of many-particle quantum systems such as fissioning nuclei. Following Ehrenfest's method, we show that the quantum kinetic force between parts of an extended quantum system can be described by an operator acting on the boundary between the two subsystems. The contribution to the force due to a short-ranged particle interaction can also be treated in the same way. This includes interaction effects treated in density functional theory by local functionals. The force operators are applied to several simple models to demonstrate the method.
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
2006.07974 [pdf]
0 citations
05
[Submitted on 14 Jun 2020]
Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers
Mark Alford🇺🇸 · Arus Harutyunyan🇦🇲 · Armen Sedrakian🇩🇪
In this paper, we discuss the damping of density oscillations in dense nuclear matter in the temperature range relevant to neutron star mergers. This damping is due to bulk viscosity arising from the weak interaction ``Urca'' processes of neutron decay and electron capture. The nuclear matter is modelled in the relativistic density functional approach. The bulk viscosity reaches a resonant maximum close to the neutrino trapping temperature, then drops rapidly as temperature rises into the range where neutrinos are trapped in neutron stars. We investigate the bulk viscous dissipation timescales in a post-merger object and identify regimes where these timescales are as short as the characteristic timescale $\sim$ 10 ms, and, therefore, might affect the evolution of the post-merger object. Our analysis indicates that bulk viscous damping would be important at not too high temperatures of the order of a few MeV and densities up to a few times saturation density.
Comments:
v2: Matches published version; v1: 19 pages, 11 figures, submitted to "Particles"
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
2006.07975 [pdf]
Particles(2020)·59 citations
06
[Submitted on 14 Jun 2020]
Neutrino mixing in nuclear rapid neutron-capture processes
M. M. Saez🇦🇷 · O. Civitarese🇦🇷 · M. E. Mosquera🇦🇷
A possible mechanism for the formation of heavy-mass elements in supernovae is the rapid neutron-capture-mechanism (r-process). It depends upon the electron-fraction $Y_{e}$ , a quantity which is determined by beta-decay-rates. In this paper, we focus on the calculation of electroweak decay-rates in presence of massive neutrinos. The resulting expressions are then used to calculate nuclear reactions entering the rapid-neutron capture. We fix the astrophysical parameters to the case of a core-collapse supernova. The neutrino sector includes a mass scheme and mixing angles for active neutrinos, and also by including the mixing between active and sterile neutrinos. The results of the calculations show that the predicted abundances of heavy-mass nuclei are indeed affected by the neutrino mixing.
Comments:
13 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2006.08043 [pdf]
IJMPE(2020)·1 citation
07
[Submitted on 15 Jun 2020]
Structure of the ground and excited states in $_{Λ}^{9}$ Be nucleus
Yu. A. Lashko🇺🇦 · A. V. Nesterov🇺🇦 · V. S. Vasilevsky🇺🇦
We investigate properties of bound and resonance states in the $_{Λ}^{9}$ Be nucleus. To reveal the nature of these states, we use a three-cluster $2 α + Λ$ microscopic model. The model incorporates Gaussian and oscillator basis functions and reduces a three-cluster Schrödinger equation to a two-body like many-channel problem with the two-cluster subsystems ( $_{Λ}^{5}$ He and $^{8}$ Be) being in a bound or a pseudo-bound state. Influence of the cluster polarization on the energy and widths of resonance states in $_{Λ}^{9}$ Be and on elastic and inelastic $_{Λ}^{5}$ He+ $α$ scattering is analyzed.
Comments:
42 pages, 5 figures, extended version of the paper, submitted to Nucl. Phys. A
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.08137 [pdf]
NPA(2021)·4 citations
08
[Submitted on 15 Jun 2020]
Analytic insights on the information content of new observables
Wei-Chia Chen · J. Piekarewicz
Uncertainty quantification has emerged as a rapidly growing field in nuclear science. Theoretical predictions of physical observables often involve extrapolations to regions that are poorly constrained by laboratory experiments and astrophysical observations. Without properly quantified theoretical errors, such model predictions are of limited value. Also, one often deals with theoretical constructs that involve fundamental quantities that are not accessible to experiment or observation. Particularly relevant in this context is the pressure of pure neutron matter. In this contribution we develop an analytic framework to answer the question of "How can new data reduce uncertainties of current theoretical models?" [P.-G. Reinhard and W. Nazarewicz, Phys. Rev. C81, 051303(R) (2010)]. Simple and insightful expressions are obtained to quantify the impact of one or two new observables on theoretical uncertainties in two critical quantities: the slope of the symmetry energy at saturation density and the pressure of pure neutron matter at twice nuclear matter saturation density.
Comments:
6 pages and 2 figures
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
2006.08405 [pdf]
PRC(2020)·2 citations
09
[Submitted on 15 Jun 2020]
Spectroscopic factors, overlaps, and isospin symmetry from an $R$ -matrix point of view
Carl R. Brune
Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: $R$ -matrix theory is used as the primary tool to interoperate between the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships among the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon+ $^{12} C$ , nucleon+ $^{16} O$ , and nucleon+ $^{26} Al$ are presented. A new approach to multi-level mirror symmetry is derived and applied to the first three $2^{+}$ states of $^{18} O$ and $^{18} Ne$ . Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^{+}$ state in $^{18} Ne$ deduced from the mirror state in $^{18} O$ is significantly larger than found in previous work. This finding has the effect of increasing the $^{17} F (p, γ)^{18} Ne$ reaction rate in novae.
Comments:
27 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.08424 [pdf]
PRC(2020)·11 citations
10
[Submitted on 15 Jun 2020]
Influence of pairing and deformation on charge exchange transitions
A. Carranza M.🇲🇽 · S. Pittel🇺🇸 · Jorge G. Hirsch🇲🇽
We describe the importance of charge-exchange reactions, and in particular Gamow-Teller transitions, in astrophysical processes and double beta decay, and in understanding of nuclear structure. We first provide an overview of the central role played by the isovector pairing and the quadrupole-quadrupole channels in the description of energy spectra and in the manifestation of collective modes, some associated with deformation of the nuclear shape. We then turned our focus to Gamow-Teller (GT) transitions in relatively light nuclei, especially in the 2p1f shell, where isoscalar pairing may be playing a role in competition with the isovector pairing that dominates in heavier regions. Following a summary of the progress made in recent years on this subject, we report a systematic shell model study aimed at providing further clarification as to how these pairing modes compete. In this study, we use a schematic Hamiltonian that contains a quadrupole-quadrupole interaction as well as both isoscalar and isovector pairing interactions. We first find an optimal set of Hamiltonian parameters for the model, to provide a starting point from which to vary the relevant pairing strengths and thus assess how this impacts the behavior of GT transitions and the corresponding energy spectra and rotational properties of the various nuclei involved in the decays. The analysis includes as an important theme a comparison with experimental data. The need to suppress the isoscalar pairing mode when treating nuclei with a neutron excess to avoid producing spurious results for the ground state spin and parity with the simplified Hamiltonian is highlighted. Varying the strength parameters for the two pairing modes is found to exhibit different but systematic effects on GT transition properties and on the corresponding energy spectra, which are detailed. (abridged)
Comments:
Review article, 16 figures, 180 references. Comments are welcome (also missing references)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.08579 [pdf]
Rev.Mex.Fis.(2020)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE