Nuclear Theory·nucl-th

Tuesday·October 6, 2020

13 papers—8 primary·5 cross-listed

01
Parametrization of the surface energy in the ETF approximation
Ubiratãn José Furtado🇫🇷 · Francesca Gulminelli🇫🇷
We perform extended Thomas-Fermi calculations in the Wigner-Seitz cell below and above neutron drip with realistic functionals. The resulting energy density is decomposed as a sum of bulk terms and a surface term, and a compressible liquid drop analytical formula is used to fit the surface tension. The effect of curvature terms and neutron skin is studied in detail. A very good reproduction of the microscopic data is obtained using an expression that depends only on the mass and charge of the cluster, showing that the in-medium modifications of the nuclear energy in the presence of an external neutron gas can be effectively accounted for in the isospin dependence of the surface tension. In this first application, aimed at establishing the fitting protocol, we concentrate on the Sly4 energy functional, but the study can be easily generalized to different functionals, and the resulting parametrizations can be used for direct applications in pasta calculations in neutron star crusts and supernova matter.
nucl-thastro-ph.HEJ.Phys.G(2020)·9 citations
02
Event-shaped-dependent cumulants in p-Pb collisions at 5.02 TeV
De-Xian Wei🇨🇳 · Li-Juan Zhou🇨🇳
In this paper, we present a novel event-shaped cumulants (ESC) response approach, based on a multi-phase transport (AMPT) model simulations, to analyze p-Pb collisions at $s_{N N}$ = 5.02 TeV. We find that the Pearson coefficients between the subset cumulants of the final harmonics $v_{2} {2 k} (k = 1, 2, 3, 4)$ and the subset cumulants of initial eccentricity $ε_{2} {2 k}$ in the ESC basis are significantly enhanced. These Pearson coefficients are strongly-dependent on the charged multiplicity, the set number of events (SNE), and only weakly-dependent on the order of the multi-particle cumulants (two-particles, four-particles, and so on). Our results show that the ESC method can suppress the event-by-event fluctuations.
nucl-thhep-phIJMPE(2022)·1 citation
03
Local spin alignment of vector mesons in relativistic heavy-ion collisions
Xiao-Liang Xia🇨🇳 · Hui Li🇨🇳 · Xu-Guang Huang🇨🇳 · Huan Zhong Huang🇨🇳
We investigate the spin alignment of vector mesons arising from locally polarized quarks and anti-quarks (local spin alignment) in heavy-ion collisions. We find that $ρ_{00} \neq = 1/3$ does not necessarily signal the global polarization of quarks and anti-quarks along the orbital angular momentum of the system, but may also originate from their local spin polarization. Such local spin polarization could be induced by local vorticity arising from the anisotropic expansion of the fireball. We further propose experimental observables that can distinguish between the local and the global spin alignments. Measurements of these observables in heavy-ion collisions can probe the vorticity pattern and shed light on the puzzles of $ϕ$ and $K^{* 0}$ spin alignments.
nucl-thPLB(2021)·94 citations
04
Was GW190814 a black hole -- strange quark star system?
I. Bombaci (Univ. Pisa and INFN Pisa)🇮🇹 · A. Drago (Univ. Ferrara and INFN Ferrara)🇮🇹 · D. Logoteta (Univ. Pisa and INFN Pisa)🇮🇹 · G. Pagliara (Univ. Ferrara and INFN Ferrara)🇮🇹 · I. Vidana (INFN Catania)🇮🇹
We investigate the possibility that the low mass companion of the black hole in the source of GW190814 was a strange quark star. This possibility is viable within the so-called two-families scenario in which neutron stars and strange quark stars coexist. Strange quark stars can reach the mass range indicated by GW190814, $M \sim (2.5 - 2.67) M_{⊙}$ due to a large value of the adiabatic index, without the need for a velocity of sound close to the causal limit. Neutron stars (actually hyperonic stars in the two-families scenario) can instead fulfill the presently available astrophysical and nuclear physics constraints which require a softer equation of state. In this scheme it is possible to satisfy both the request of very large stellar masses and of small radii while using totally realistic and physically motivated equations of state. Moreover it is possible to get a radius for a 1.4 $M_{⊙}$ star of the order or less than 11 km, which is impossible if only one family of compact stars exists.
nucl-thastro-ph.HEPRL(2021)·133 citations
05
Chiral extrapolation of the magnetic polarizability of the neutral pion
Fangcheng He🇨🇳 · D. B. Leinweber🇦🇺 · A. W. Thomas🇦🇺 · P. Wang🇨🇳
The magnetic polarizability of the neutral pion has been calculated in the background magnetic-field formalism of Lattice QCD. In this investigation, the chiral extrapolation of these lattice results is considered in a formalism preserving the exact leading nonanalytic terms of chiral perturbation theory. The $n_{f} = 2 + 1$ numerical simulations are electro-quenched, such that the virtual sea-quarks of the QCD vacuum do not interact with the background field. To understand the impact of this, we draw on partially quenched chiral perturbation theory and identify the leading contributions of quark-flow connected and disconnected diagrams. While electro-quenching does not impact the leading-loop contribution to the magnetic polarizability, the loops which generate the leading term have yet to be considered in lattice QCD simulations. Lattice QCD results are used to constrain the analytic terms in the chiral expansion and supplementing those with the two-loop result from chiral perturbation theory enables an evaluation of the polarizability at the physical quark mass. The resulting magnetic polarizability of the neutral pion is $β_{π^{0}} = 3.44 (19)^{stat} (37)^{syst} \times 1 0^{- 4}$ fm $^{3}$ , which lies just above the $1 σ$ error bound of the experimental measurement.
nucl-thhep-latPRD(2020)·6 citations
06
A novel theoretical approach for the study of resonances in weakly bound systems
Mahamadun Hasan · Shamim Haque Mondal · Murshid Alam · Tasrief Surungan · Md Abdul Khan
In this paper, a novel theoretical scheme is presented to investigate resonant levels in weakly bound nuclear systems by the use of isospectral potentials. In this scheme, a new potential is constructed which is strictly isospectral with the original shallow-well potential and has properties that are desirable to calculate resonances more accurately and easier. Effectiveness of the method has been had been demonstrated in terms of its application to the first $0^{+}$ resonances in the neutron-rich isotopes $^{A}$ C ( $\equiv^{A - 2}$ C+n+n) in the three-body cluster model for A=18, 20.
nucl-th0 citations
07
Propagation of Hauser-Feshbach uncertainty estimates to r-process nucleosynthesis: Benchmark of statistical property models for neutron rich nuclei far from stability
S. Nikas · G. Perdikakis · M. Beard · R. Surman · M.R. Mumpower · P. Tsintari
Multimessenger observations of the neutron star merger event GW170817 have re-energized the debate over the astrophysical origins of the most massive elements via the r-process nucleosynthesis. A key aspect of such studies is comparing astronomical observations to theoretical nucleosynthesis yields in a meaningful way. To perform realistic nucleosynthesis calculations, understanding the uncertainty in microphysics details such as nuclear reaction rates is as essential as understanding uncertainties in modeling the astrophysical environment. We present an investigation of neutron capture rate calculations' uncertainty away from stability using the Hauser-Feshbach model. We provide a quantitative measure of the calculations' dependability when we extrapolate models of statistical properties to nuclei in an r-process network. We select several level density and gamma-ray strength models appropriate for neutron-capture and use them to calculate the reaction rate for each nucleus in the network. We observe how statistical properties affect the theoretical reaction rates. The rates are then sampled with the Monte Carlo technique and used in network calculations to map the range of possible r-process abundances. The results show that neutron capture rates can vary by a couple of orders of magnitude between calculations. Phenomenological models provide smoother results than semi-microscopic. They cannot, however, reproduce nuclear structure changes such as shell closures. While semi-microscopic models predict nuclear structure effects away from stability, it is not clear that these results are quantitatively accurate. The effect of the uncertainty on r-process yields is large enough to impede comparisons between observation and calculations. Progress in developing better microscopic models of gamma strengths and level densities is urgently needed to improve the fidelity of r-process models.
nucl-thastro-ph.SR15 citations
08
Few-neutron systems with the long-range Casimir-Polder force
R. Higa🇧🇷 · J. F. Babb🇺🇸
In this work we present results of the long-range electromagnetic Casimir-Polder interactions between two neutrons, a neutron and a conducting wall, and a neutron between two walls. As input, we use the dynamic dipole polarizabilities of the neutron fitted to chiral EFT results up to the pion production threshold and at the onset of the Delta resonance. Our work can be relevant to the physics of confined ultracold neutrons inside bottles.
nucl-thhep-phphysics.atom-phBraz.J.Phys.(2021)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE