Nuclear Theory·nucl-th

Friday·November 18, 2022

16 papers—8 primary·8 cross-listed

01
[Submitted on 16 Nov 2022]
Helicity and vorticity in heavy-ion collisions at NICA energies
N. S. Tsegelnik🇷🇺 · E. E. Kolomeitsev🇷🇺 · V. Voronyuk🇷🇺
Heavy-ion collisions at center-of-mass nucleon collision energies 4.5--11.5 GeV are analyzed within the PHSD transport model. Spectator nucleons are separated, and the transfer of the initial angular momentum of colliding nuclei to the fireball formed by participants is studied. The maximal angular momentum is carried by the fireball in gold-gold collisions with the impact parameter about 5 fm corresponding to centrality class 10--20\%. The obtained participant distributions were fluidized and the energy and baryon number densities, temperature, and velocity fields are obtained in the Landau frame. It is shown that the velocity field has dominantly Hubble-like transversal and longitudinal expansion with the vortical motion being only a small correction on top of it. The vorticity field is calculated and illustrated in detail. The formation of two oppositely-rotating vortex rings moving in opposite directions along the $z$ axis is demonstrated. Other characteristics of the vortical motion such as the Lamb vector field and the kinematic vorticity number are considered. The magnitude of the latter one is found to be smaller than that for the Poiseuille flow and close to the pure shear deformation corresponding to just a flattening of fluid cells. The field of hydrodynamic helicity, which is responsible for the axial vortex effect, is calculated. The separation of positive and negative helicities localized upper and lower semi-planes with respect to the reaction plane is shown. It is proved that the areas with various helicity signs can be probed by the selection of $Λ$ hyperons with positive and negative projections of their momenta orthogonal to the reaction plane.
Comments:
22 pages, 23 figures. Figure labels are corrected, references added, figure labels are rescaled
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2211.09219 [pdf]
PRC(2023)·24 citations
02
[Submitted on 17 Nov 2022]
Weinberg and few-nucleon forces
U. van Kolck🇫🇷
Weinberg's contributions to the power counting and derivation of few-nucleon forces in Chiral EFT are briefly recalled. Subsequent improvements are reviewed, concluding with the recent suggestion of a combinatorial enhancement.
Comments:
7 pages. Invited talk at the XLIV Reuniao de Trabalho sobre Fisica Nuclear no Brasil, November 2021
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2211.09271 [pdf]
J.Phys.Conf.Ser.(2022)·0 citations
03
[Submitted on 17 Nov 2022]
The interplay of single-particle and collective motions in the low-lying states of $_{Λ}^{21}$ Ne with quadrupole-octupole correlations
H. J. Xia🇨🇳 · X. Y. Wu🇨🇳 · H. Mei🇷🇺 · J. M. Yao🇨🇳
The beyond mean-field approach for low-lying hypernuclear states is extended by mixing the configurations associated with both single-particle and quadrupole-octupole collective excitations within the generator coordinate method based on a covariant density functional theory. The method is demonstrated in the application to the low-lying states of $_{Λ}^{21}$ Ne, where the configurations with the $Λ$ hyperon occupying the first ( $Λ_{s}$ ) and second ( $Λ_{p}$ ) lowest-energy states are considered. The results indicate that the positive-parity states are dominated by the $α +^{12}$ C+ $α + Λ_{s}$ structure. In contrast, the low-lying negative-parity states are dominated by a strong admixture of $α +^{16}$ O+ $Λ_{s}$ structure and $α +^{12}$ C+ $α + Λ_{p}$ structure due to the inclusion of octupole correlations. As a result, the low-lying negative-parity states become much lower than what is expected from the previous studies without the mixing, and the electric multipole transition strengths are significantly quenched.
Comments:
9 pages with 5 figures and 2 tables
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2211.09356 [pdf]
SCPMA(2023)·10 citations
04
[Submitted on 17 Nov 2022]
Isotopic dependence of $(n, α)$ reaction cross sections for Fe and Sn nuclei
Sema Kucuksucu · Mustafa Yigit · Nils Paar
The $(n, α)$ reactions play an important role for the energy generation and the synthesis of chemical elements in the stars, as well as for nuclear engineering and medical applications. The aim of this study is to explore the evolution of $(n, α)$ reactions in Fe and Sn isotope chains in order to assess their properties with the increase of neutrons in target nucleus, and compare with other relevant neutron induced reactions. Model calculations of the cross sections are based on the statistical Hauser-Feshbach model in TALYS implementation, using global optical model potential that is additionally adjusted by the $(n, α)$ cross section data for $^{54}$ Fe and $^{118}$ Sn. The calculations of $(n, α)$ reactions in Fe and Sn isotopes provide the insight into their isospin dependence and properties over the complete relevant range of neutron energies. The results show the evolution of the cross sections with pronounced maxima at low-mass isotopes, and rather strong decrease for neutron-rich nuclei consistent with the reduction of the reaction $Q$ -value and increased contributions from other exit channels from compound nucleus. The analysis of the Maxwellian averaged cross sections at temperatures in stellar environment shows that while the $(n, α)$ reactions contribute for the low-mass isotopes, in neutron induced reactions with nuclei with neutron excess, $γ$ and neutron emission dominate.
Comments:
14 pages, 14 figures
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
2211.09411 [pdf]
NPA(2024)·1 citation
05
[Submitted on 17 Nov 2022]
Fermi operator expansion method for nuclei and inhomogeneous matter with nuclear energy density functional
Takashi Nakatsukasa
The nuclear energy density functional method at finite temperature is a useful tool for studies of nuclear structure at high excitation, and also for researches of nuclear matter involved in explosive stellar phenomena and neutron stars. However, its unrestricted calculation requires large computational costs for the three-dimensional coordinate-space solvers, especially for the Hamiltonian matrix diagonalization and (or) the Gram-Schmidt orthonormalization of the single-particle wave functions. We test numerical performance of the Fermi operator expansion method, that requires neither the diagonalization nor the Gram-Schmidt orthonormalization, for finite nuclei and inhomogeneous nuclear matter. The method is applied to isolated finite N=Z nuclei and to non-uniform symmetric nuclear matter at finite temperature, which turns out be very effective with the three-dimensional coordinate-space representation, especially at high temperature. The Fermi operator expansion method is a useful tool for studies of various nuclear phases at finite temperature with the energy density functional calculations. The method is suitable for massively parallel computing with distributed memory. Furthermore, when the space size is large, the calculation may benefit from its order-N scaling property.
Comments:
14 pages, 16 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2211.09448 [pdf]
PRC(2023)·2 citations
06
[Submitted on 17 Nov 2022]
Cluster mean field description of alpha emission
A. Dumitrescu · D. S. Delion
We show that the Hartree-Fock-Bogoliubov (HFB) method is able to describe experimental values of alpha decay widths by including a residual nucleon-nucleon Surface Gaussian Interaction (SGI) within the standard procedure used to calculate the nuclear mean field. We call this method the Cluster HFB (CHFB) approach. In this way we correct the deficient asymptotic behaviour of the corresponding single-particle (sp) wave functions generated by the standard mean field. The corrected mean field becomes a sum between the standard mean Woods-Saxon-like field and a cluster Gaussian component centered at the same radius as the SGI. Thus, we give a confirmation of the mean field plus cluster potential structure, which was assumed in our previous work on alpha-decay widths. Systematic calculations evidence the linear correlation between the SGI strength and fragmentation potential, allowing for reliable predictions concerning the half lives of superheavy emitters.
Comments:
12 pages, 8 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2211.09452 [pdf]
PRC(2023)·8 citations
07
[Submitted on 17 Nov 2022]
Charge diffusion in relativistic resistive second-order dissipative magnetohydrodynamics
Ashutosh Dash🇩🇪 · Masoud Shokri🇩🇪 · Luciano Rezzolla🇩🇪 · Dirk H. Rischke🇩🇪
We study charge diffusion in relativistic resistive second-order dissipative magnetohydrodynamics. In this theory, charge diffusion is not simply given by the standard Navier-Stokes form of Ohm's law, but by an evolution equation which ensures causality and stability. This, in turn, leads to transient effects in the charge diffusion current, the nature of which depends on the particular values of the electrical conductivity and the charge-diffusion relaxation time. The ensuing equations of motion are of so-called stiff character, which requires special care when solving them numerically. To this end, we specifically develop an implicit-explicit Runge-Kutta method for solving relativistic resistive second-order dissipative magnetohydrodynamics and subject it to various tests. We then study the system's evolution in a simplified 1+1-dimensional scenario for a heavy-ion collision, where matter and electromagnetic fields are assumed to be transversely homogeneous, and investigate the cases of an initially non-expanding fluid and a fluid initially expanding according to a Bjorken scaling flow. In the latter case, the scale invariance is broken by the ensuing self-consistent dynamics of matter and electromagnetic fields. However, the breaking becomes quantitatively important only if the electromagnetic fields are sufficiently strong. The breaking of scale invariance is larger for smaller values of the conductivity. Aspects of entropy production from charge diffusion currents and stability are also discussed.
Comments:
23 pages, 14 figures. Revised discussion on entropy production, and new comparison plot with Strang-Splitting method
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Fluid Dynamics (physics.flu-dyn)
arXiv:
2211.09459 [pdf]
PRD(2023)·27 citations
08
[Submitted on 17 Nov 2022]
Calculating QCD Phase Diagram Trajectories of Nuclear Collisions using a Semi-analytical Model
Todd Mendenhall🇺🇸 · Zi-Wei Lin🇺🇸
At low to moderate collision energies where the parton formation time $τ_{F}$ is not small compared to the nuclear crossing time, the finite nuclear thickness significantly affects the energy density $ϵ (t)$ and net conserved-charge densities such as the net-baryon density $n_{B} (t)$ produced in heavy ion collisions. As a result, at low to moderate energies the trajectory in the QCD phase diagram is also affected by the finite nuclear thickness. Here, we first discuss our semi-analytical model and its results on $ϵ (t)$ , $n_{B} (t)$ , $n_{Q} (t)$ , and $n_{S} (t)$ in central Au+Au collisions. We then compare the $T (t)$ , $μ_{B} (t)$ , $μ_{Q} (t)$ , and $μ_{S} (t)$ extracted with the ideal gas equation of state (EoS) with quantum statistics to those extracted with a lattice QCD-based EoS. We also compare the $T - μ_{B}$ trajectories with the RHIC chemical freezeout data. Finally, we discuss the effect of transverse flow on the trajectories.
Comments:
4 pages, proceedings for the 20th International Conference on Strangeness in Quark Matter (SQM2022)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2211.09651 [pdf]
EPJ Web Conf.(2023)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE