Nuclear Theory·nucl-th

Tuesday·March 5, 2019

15 papers—11 primary·4 cross-listed

01
[Submitted on 2 Mar 2019]
Dynamics of clusters and fragments in heavy-ion collisions
Akira Ono🇯🇵
A review is given on the studies of formation of light clusters and heavier fragments in heavy-ion collisions at incident energies from several tens of MeV/nucleon to several hundred MeV/nucleon, focusing on dynamical aspects and on microscopic theoretical descriptions. Existing experimental data already clarify basic characteristics of expanding and fragmenting systems typically in central collisions, where cluster correlations cannot be ignored. Cluster correlations appear almost everywhere in excited low-density nuclear many-body systems and nuclear matter in statistical equilibrium where the properties of a cluster may be influenced by the medium. On the other hand, transport models to solve the time evolution have been developed based on the single-nucleon distribution function. Different types of transport models are reviewed putting emphasis both on theoretical features and practical performances in the description of fragmentation. A key concept to distinguish different models is how to consistently handle single-nucleon motions in the mean field, fluctuation or branching induced by two-nucleon collisions, and localization of nucleons to form fragments and clusters. Some transport codes have been extended to treat light clusters explicitly. Results indicate that cluster correlations can have strong impacts on global collision dynamics and correlations between light clusters should also be taken into account.
Comments:
review article, 64 pages, 27 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1903.00608 [pdf]
PPNP(2019)·112 citations
02
[Submitted on 3 Mar 2019]
Detailed illustration of accuracy of presently used nuclear-mass models
Adam Sobiczewski · Yuri A. Litvinov · Michal Palczewski
The accuracy of description of measured nuclear masses by presently used nuclear-mass models is studied. Twelve models of various kinds are considered, eleven of the global character and one local model specially adapted to description of heavy nuclei. To decrease the number of nuclei over which the accuracy is averaged, the global region (Z,N >= 8) is divided into four subregions, in which the accuracy is studied separately. Still, to reach the best precision, the accuracy is finally investigated without any averaging, for each nucleus separately. The results are presented in a form of colored maps, large enough to be easily and accurately read. Besides the accuracy of the studied models, also their predictive power is considered. It is found that the accuracy of description of mass strongly depends on a nuclear-mass model and on the region of nuclei to which the model is applied. The best accuracy is obtained by the recent two Chinese models WS3+ and WS4+. Generally, no clear, strong correlation between the accuracy of description of already known masses by a given model and its predictive power for new masses is observed. Still, such correlation is found for separate models and in separate regions of nuclei. More often for the macroscopic-microscopic models than for the other approaches.
Comments:
70 pages
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.00886 [pdf]
Atom.Data Nucl.Data Tabl.(2018)·33 citations
03
[Submitted on 4 Mar 2019]
Isoscalar dipole excitations in $^{16}$ O
Yoshiko Kanada-En'yo · Yuki Shikata
Isoscalar (IS) monopole and dipole excitations in $^{16}$ O were investigated by the method of shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method. Significant strengths of the IS monopole and dipole transitions were obtained in the low-energy region below the giant resonances. In addition to the compressive mode, which mainly contributes to the high-energy strengths for the IS dipole giant resonance, we obtained a variety of low-energy dipole modes such as the vortical dipole mode in the $1_{1}^{-}$ state of the vibrating tetrahedral $4 α$ and the $^{12}$ C+ $α$ cluster structure in the $1_{2}^{-}$ state. The $1_{1}^{-}$ state contributes to the significant low-energy strength of the IS dipole transition as 5\% of the energy-weighted sum rule, which describes well the experimental data observed by the $α$ inelastic scattering.
Comments:
10 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.01075 [pdf]
PRC(2019)·18 citations
04
[Submitted on 4 Mar 2019]
A new spectroscopic probe to search for magic numbers at high-excitation energies
Cebo Ngwetsheni · Nico Orce
Empirical drops in ground-state nuclear polarizabilities indicate deviations from the effect of giant dipole resonances and may reveal the presence of shell effects in semi-magic nuclei with neutron magic numbers $N = 50$ , 82 and 126. Similar drops of polarizability in the quasi-continuum of nuclei with, or close to, magic numbers $N = 28$ , 50 and 82, could reflect the continuing influence of shell closures up to the nucleon separation energy. These findings open a new avenue to investigating magic numbers at high-excitation energies and strongly support recent large-scale shell-model calculations in the quasi-continuum region, which describe the origin of the low-energy enhancement of the photon strength function as induced paramagnetism. The nuclear-structure dependence of the photon-strength function asserts the generalized Brink-Axel hypothesis as more universal than originally expected.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1903.01122 [pdf]
0 citations
05
[Submitted on 4 Mar 2019]
Multiple $S U (3)$ algebras in shell model and \\ interacting boson model
V.K.B. Kota🇮🇳 · R. Sahu🇮🇳 · P.C. Srivastava🇮🇳
Rotational $S U (3)$ algebraic symmetry continues to generate new results in the shell model (SM). Interestingly, it is possible to have multiple $S U (3)$ algebras for nucleons occupying an oscillator shell $η$ . Several different aspects of the multiple $S U (3)$ algebras are investigated using shell model and also deformed shell model based on Hartree-Fock single particle states with nucleons in $s d g$ orbits giving four $S U (3)$ algebras. Results show that one of the $S U (3)$ algebra generates prolate shapes, one oblate shape and the other two also generate prolate shape but one of them gives quiet small quadrupole moments for low-lying levels. These are inferred by using the standard form for the electric quadrupole transition operator and using quadrupole moments and $B (E 2)$ values in the ground $K = 0^{+}$ band in three different examples. Multiple $S U (3)$ algebras extend to interacting boson model and using $s d g$ IBM, the structure of the four $S U (3)$ algebras in this model are studied by coherent state analysis and asymptotic formulas for $E 2$ matrix elements. The results from $s d g$ IBM further support the conclusions from the $s d g$ shell model examples.
Comments:
27 pages, 2 figures, 7 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.01131 [pdf]
Bulg.J.Phys.(2019)·0 citations
06
[Submitted on 4 Mar 2019]
Possible $S$ -wave $N D^{(*)}$ and $N B ˉ^{(*)}$ bound states in a chiral quark model
Dan Zhang🇨🇳 · Dan Yang🇨🇳 · Xiao-Fei Wang🇨🇳 · Kanzo Nakayama🇺🇸
$S$ -wave bound-states composed of a nucleon( $N$ ) and a heavy meson ( $D$ , $D^{*}$ , $B ˉ$ or $B ˉ^{*}$ ) are investigated in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving the resonating group method equation. The results reveal that the $N D$ and $N D^{*}$ interactions in the corresponding relative $S$ -wave states are attractive, arising mainly from one boson exchange processes between light quarks. It is shown that these attractions are strong enough to form six $N D$ and $N D^{*}$ $S$ -wave bound states in the extended chiral SU(3) quark model with the binding energies in the range of $3 - 45$ MeV, and three $S$ -wave bound states within the chiral SU(3) quark model with binding energies of $2 - 8$ MeV. In particular, the experimentally observed $Σ_{c} (2800)$ is interpreted to be most likely an $S -$ wave $N D$ state with the total isopsin $I = 0$ and spin-parity $J^{P} = 1/ 2^{-}$ , while $Λ_{c} (2940)^{+}$ as an $S -$ wave $N D^{*}$ state with $I = 0$ and $J^{P} = 3/ 2^{-}$ . Further information on the $N D$ and $N D^{*}$ interactions in the (unbound) scattering kinematics are obtained from the corresponding $S$ -wave phase shifts. The $N B ˉ$ and $N B ˉ^{*}$ systems are also investigated within the present two models and some $S -$ wave bound states with binding energies in the range of $1 - 60$ MeV are predicted in these systems: six (in total) within the extended chiral SU(3) quark model and, four, within the chiral SU(3) quark model.
Comments:
11 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.01207 [pdf]
11 citations
07
[Submitted on 4 Mar 2019]
Reply to "Comment on "How (not) to renormalize integral equations with singular potentials in effective field theory"
E. Epelbaum🇩🇪 · A. M. Gasparyan🇷🇺 · J. Gegelia🇩🇪 · Ulf-G. Meißner🇩🇪
We offer a brief response to the criticism put forward by Pavon Valderrama about our recent paper on "How (not) to renormalize integral equations with singular potentials in effective field theory".
Comments:
2 pages, no figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
arXiv:
1903.01273 [pdf]
EPJA(2019)·14 citations
08
[Submitted on 1 Mar 2019]
Note on neutron star equation of state in the light of GW170817
Ang Li🇨🇳 · Zhen-Yu Zhu🇨🇳
From the very first multimessenger event of GW170817, clean robust constraints can be obtained for the tidal deformabilities of the two stars involved in the merger, which provides us unique opportunity to study the equation of states (EOSs) of dense stellar matter. In this contribution, we employ a model from the quark level, describing consistently a nucleon and many-body nucleonic system from a quark potential. We check that our sets of EOSs are consistent with available experimental and observational constraints at both sub-nuclear saturation densities and higher densities. The agreements with ab-initio calculations are also good. Especially, we tune the density dependence of the symmetry energy (characterized by its slope at nuclear saturation $L$ ) and study its influence on the tidal deformability. The so-called $QM F 18$ EOS is named after the case of $L = 40 MeV$ , and it gives $M_{TOV} = 2.08 M_{⊙}$ and $R = 11.77 km$ , $Λ = 331$ for a $1.4 M_{⊙}$ star. The tidal signals are demonstrated to be insensitive to the uncertain crust-core matching, despite the good correlation between the symmetry energy slope and the radius of the star.
Comments:
8 pages, 6 figures, Submitted to the AIP Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy, Jan. 3-7, Xiamen, China
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex)
arXiv:
1903.01280 [pdf]
AIP Conf.Proc.(2019)·2 citations
09
[Submitted on 1 Mar 2019]
Cooling of hypernuclear compact stars: Hartree-Fock models and high-density pairing
Adriana R. Raduta🇷🇴 · Jia Jie Li🇩🇪 · Armen Sedrakian🇩🇪 · Fridolin Weber🇺🇸
The thermal evolution of hypernuclear compact stars is studied for stellar models constructed on the basis of covariant density functional theory in Hartree and Hartree-Fock approximation. Parametrizations of both types are consistent with the astrophysical mass constraints on compact stars and available hypernuclear data. We discuss the differences of these density functionals and highlight the effects they have on the composition and on the cooling of hypernuclear stars. It is shown that hypernuclear stars computed with density functional models that have a low symmetry energy slope, $L$ , are fairly consistent with the cooling data of observed compact stars. The class of stellar models based on larger $L$ values gives rise to the direct Urca process at low densities, which leads to significantly faster cooling. We conjecture high-density pairing for protons and $Λ$ 's in the $P$ -wave channel and provide simple scaling arguments to obtain these gaps. As a consequence the most massive stellar models with masses $1.8 \leq M / M_{⊙} \leq 2$ experience slower cooling by hyperonic dUrca processes which involve $Λ$ 's and protons.
Comments:
15 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
1903.01295 [pdf]
MNRAS(2019)·36 citations
10
[Submitted on 4 Mar 2019]
Systematics of toroidal dipole modes in Ca, Ni, Zr, and Sn isotopes
A. Repko · V.O. Nesterenko · J. Kvasil · P.-G. Reinhard
We analyze the relation between isoscalar toroidal modes and so-called pygmy dipole resonance (PDR) which both appear in the same region of low-energy dipole excitations. To this end, we use a theoretical description within the fully self-consistent Skyrme quasiparticle random-phase approximation (QRPA). Test cases are spherical nuclei $^{40, 48}$ Ca, $^{58, 72}$ Ni, $^{90, 100}$ Zr, and $^{100, 120, 132}$ Sn which cover four different elements and for each element at least two isotopes with different neutron excess, one small and another large. The structure of the modes is investigated in terms of strength functions, transition densities (TD) and transition currents (TC). For all considered nuclei, we see that, independently on whether PDR strength exists or not, the flow pattern in the lower part of the "PDR energy region" is basically the isoscalar vortical toroidal motion with a minor irrotational fraction. A one-to-one correspondence between calculated TD and TC can be established. The toroidal flow appears already in the uncoupled two-quasiparticle (2qp) excitations and becomes definitively strong for the QRPA modes. Altogether, we find that low-lying dipole strength often denoted as isoscalar PDR is actually an oversimplified imitation of the basically toroidal motion in nuclei with a sufficient neutron excess.
Comments:
12 pages, 14 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.01348 [pdf]
EPJA(2019)·23 citations
11
[Submitted on 4 Mar 2019]
Gluon Radiation from a Classical Point Particle
Keijo Kajantie🇫🇮 · Larry D. McLerran🇺🇸 · Risto Paatelainen🇫🇮
We consider an initially at rest colored particle which is struck by an ultra-relativistic nucleus. The particle is treated classically both with respect to its motion and its color charge. The nucleus is treated as a sheet of colored glass within the context of the Color Glass Condensate framework. We compute both the momentum and coordinates of the struck classical particle and the emitted radiation. Our computations generalize the classic electrodynamics computation of the radiation of an accelerated charged particle to include the radiation induced by the charged gluon field. This latter contribution adds to the classic electrodynamics result and produces a gluon rapidity distribution that is roughly constant as a function of rapidity at rapidities far from the fragmentation region of the struck particles. These computations may form the basis of a first principles treatment for the initial conditions for the evolution of matter produced in the fragmentation region of asymptotically high energy collisions.
Comments:
26 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1903.01381 [pdf]
PRD(2019)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE