Nuclear Theory·nucl-th

Tuesday·April 16, 2019

13 papers—9 primary·4 cross-listed

01
[Submitted on 13 Apr 2019]
Study of the core-crust transition in neutron stars with finite-range interactions: the dynamical method
C. Gonzalez-Boquera · M. Centelles · X. Viñas · T. R. Routray
The properties of the core-crust transition in neutron stars are investigated using effective nuclear forces of finite-range. Special attention is paid to the so-called dynamical method for locating the transition point, which, apart from the stability of the uniform nuclear matter against clusterization, also considers contributions due to finite-size effects. In particular, contributions to the transition density and pressure from the direct and exchange energies are carefully analyzed. To this end, finite-range forces of Gogny, Modified Gogny Interaction (MDI) and Simple Effective Interaction (SEI) types are used in the numerical applications. The results from the dynamical approach are compared with those from the popular thermodynamical method that neglects the surface and Coulomb effects in the stability condition. The dependence of the core-crust transition on the stiffness of the symmetry energy of the finite-range models is also addressed. Finally, we analyze the impact of the transition point on the mass, thickness and fraction of the moment of inertia of the neutron star crust. Prominent differences in these crustal properties of the star are found between using the transition point obtained with the dynamical method or the thermodynamical method. It is concluded that the core-crust transition needs to be ascertained as precisely as possible in order to have realistic estimates of the observed phenomena where the crust plays a significant role.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06566 [pdf]
PRC(2019)·36 citations
02
[Submitted on 13 Apr 2019]
Hydrodynamic flow in small systems, or: "How the heck is it possible that a system emitting only a dozen particles can be described by fluid dynamics?"
Ulrich W. Heinz (Ohio State University)🇺🇸 · J. Scott Moreland (Duke University)🇺🇸
The "unreasonable effectiveness" of relativistic fluid dynamics in describing high energy heavy-ion and even proton-proton collisions are demonstrated and discussed. Several recent ideas of optimizing relativistic fluid dynamics for the specific challenges posed by such collisions will be presented, and some thoughts will be offered why the framework works better than originally expected. I will also address the unresolved question where exactly hydrodynamics breaks down, and why.
Comments:
Talk presented at KRUGER-2018, Hazyview, Mpumalanga, South Africa, Dec. 3-8, 2018, to appear in the proceedings, published in the Open Access Journal of Physics: Conference Series (JPCS)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1904.06592 [pdf]
J.Phys.Conf.Ser.(2019)·39 citations
03
[Submitted on 14 Apr 2019]
$α$ -cluster structure above double-shell closures and $α$ -decay of $^{104}$ Te
M. A. Souza · H. Miyake · T. Borello-Lewin · C. A. da Rocha · C. Frajuca
An analysis of the $α$ + core properties of $^{104}$ Te along with a global discussion on the $α$ -cluster structure above the double-shell closures is presented from the viewpoint of the local potential model. The $α$ + core interaction is described by a nuclear potential of (1 + Gaussian) $\times$ (W.S. + W.S. $^{3}$ ) shape with two free parameters, which has been successfully tested in nuclei of different mass regions. The model produces $Q_{α}$ values and $α$ -decay half-lives for $^{104}$ Te in agreement with the 2018 experimental data of Auranen et al. in the energy range $5.13 MeV < Q_{α} < 5.3 MeV$ using an $α$ preformation factor $P_{α} = 1$ . The comparison of the calculated reduced $α$ -widths for the ground state bands of $^{104}$ Te, $^{94}$ Mo and $^{212}$ Po indicates that $^{104}$ Te has an $α$ -cluster degree significantly higher than $^{94}$ Mo and much higher than $^{212}$ Po. These results point to $^{104}$ Te as a preferential nucleus for $α$ -clustering in the $N, Z = 50$ region and corroborate the statement on the superallowed $α$ -decay in $^{104}$ Te.
Comments:
11 pages, 3 figures. Accepted for publication in Physics Letters B
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06657 [pdf]
PLB(2019)·18 citations
04
[Submitted on 14 Apr 2019]
Diabatic scission paths
G.F. Bertsch · W. Younes · L.M. Robledo
An outstanding problem in the theory of nuclear fission is to understand the Hamiltonian dynamics at the scission point. In this work the fissioning nucleus is modeled in self-consistent mean-field theory as a set of Generator Coordinate (GCM) configurations passing through the scission point. In contrast to previous methods, the configurations are constructed in the Hartree-Fock approximation with axially symmetric mean fields and using the K-partition numbers as additional constraints. The goal of this work is to find paths through the scission point where the overlaps between neighboring configurations are large. A measure of distance along the path is proposed that is insensitive to the division of the path into short segments. For most of the tested K-partitions two shape degrees of freedom are adequate to define smooth paths. However, some of the configurations and candidate paths have sticking points where there are substantial changes in the many-body wave function, especially if quasiparticle excitations are present. The excitation energy deposited in fission fragments arising from thermal excitations in the pre-scission configurations is determined by tracking orbital occupation numbers along the scission paths. This allows us to assess the validity of the well-known scission-point statistical model, in which the scission process is assumed to be fully equilibrated up to the separated fission fragments. The nucleus 236U is taken as a representative example in the calculations.
Comments:
To be submitted to Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06751 [pdf]
PRC(2019)·9 citations
05
[Submitted on 14 Apr 2019]
Truncation scheme of time-dependent density-matrix approach III
Mitsuru Tohyama🇯🇵 · Peter Schuck🇫🇷
The time-dependent density-matrix theory (TDDM) where the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy for reduced density matrices is truncated by approximating a three-body density matrix with one-body and two-body density matrices is applied to the Lipkin model. It is shown that in the large $N$ limit the ground state in TDDM approaches the exact solution. Various truncation schemes for the three-body density matrix are also tested for an extended three-level Lipkin model.
Comments:
11 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06780 [pdf]
EPJA(2019)·5 citations
06
[Submitted on 15 Apr 2019]
Equation of State for Neutron Stars in the Quark-Meson Coupling Model with the Cloudy Bag
Tsuyoshi Miyatsu🇯🇵 · Koichi Saito🇯🇵
Using the quark-meson coupling model with the cloudy bag, we construct the equation of state for neutron stars with hyperons in SU(3) flavor symmetry. The hyperfine interaction due to the gluon exchange and the pion-cloud effect inside a baryon is taken into account in vacuum and nuclear matter. We investigate how the quark degrees of freedom and the exchanges of gluon and pion between two quarks affect the properties of nuclear and neutron-star matter. It is found that the variation of baryon substructure in matter plays an important role in supporting massive neutron stars.
Comments:
4 papes, 3 figures, 2 tables, accepted to the proceedings of the 8th International Conference on Quarks and Nuclear Physics (QNP2018) in JPS Conference Proceedings
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06856 [pdf]
JPS Conf.Proc.(2019)·2 citations
07
[Submitted on 15 Apr 2019]
Correlations with fluctuating strings
Wojciech Broniowski🇵🇱 · Martin Rohrmoser🇵🇱
We present a semi-analytic approach to forward-backward multiplicity correlations in ultra-relativistic nuclear collisions, based on particle emission from strings with fluctuating end-points. We show that with the constraints from rapidity spectra, one can obtain bounds for the magnitude of the standard measures of the forward-backward fluctuations. The method is generic under the assumption of independent production from sources. For definiteness, we use the wounded quark model for Au+Au and d+Au collisions at the energy of $s_{N N} = 200$ GeV.
Comments:
Talk presented by WB at XXV Cracow Epiphany Conference on Advances in Heavy Ion Physics, 8-11 January 2019
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.06955 [pdf]
Acta Phys.Polon.B(2019)·0 citations
08
[Submitted on 15 Apr 2019]
Sensitivity of the evaporation residue observables to the symmetry energy
S. Mallik🇮🇳 · G. Chaudhuri🇮🇳 · F. Gulminelli🇫🇷
The static properties of the heaviest residue and unbound particles produced in central $^{64, 58} N i$ on $^{64, 58} N i$ collisions at 50 MeV/nucleon are predicted within the BUU transport model, in order to explore the sensitivity of those observables to the density dependence of the symmetry energy. We include fluctuations in the collision integral and use a meta-modelling for the mean-field which allows an independent variation of the different empirical parameters of the equation of state. We find that the isospin ratio of pre-equilibrium particles is a good estimator of the stiffness of the symmetry energy, in agreement with previous works. In addition to that, whatever be the functional form of the equation of state, we show that a higher symmetry energy at subsaturation densities leads to an increased size and isotopic ratio for the heaviest residue. This is understood in terms of energy sharing between the pre-equilibrium particles and the (quasi)fused system. The combination of the two observables might be an interesting tool to constrain the different density dependence below and above saturation, which is linked to the relatively poorly known parameter $K_{sy m}$ .
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1904.06958 [pdf]
PRC(2019)·13 citations
09
[Submitted on 15 Apr 2019]
Momentum-space probability density of $^{6}$ He in Halo Effective Field Theory
M. Göbel · H.-W. Hammer · C. Ji · D. R. Phillips
We compute the momentum-space probability density of $^{6}$ He at leading order in Halo EFT. In this framework, the $^{6}$ He nucleus is treated as a three-body problem with a $^{4}$ He core ( $c$ ) and two valence neutrons ( $n$ ). This requires the $nn$ and $n c$ t-matrices as well as a $c nn$ force as input in the Faddeev equations. Since the $n c$ t-matrix corresponds to an energy-dependent potential, we consider the consequent modifications to the standard normalization and orthogonality conditions. We find that these are small for momenta within the domain of validity of Halo EFT. In this regime, the $^{6}$ He probability density is regulator independent, provided the cutoff is significantly above the EFT breakdown scale.
Comments:
34 pages, 3 figures, version to appear in Few-Body Systems. Further explanations and discussions added, typos corrected, results unchanged
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1904.07182 [pdf]
Few Body Syst.(2019)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE