Nuclear Theory·nucl-th

Wednesday·January 8, 2020

15 papers—8 primary·7 cross-listed

01
[Submitted on 7 Jan 2020]
Exploring two-neutron halo formation in the ground-state of $^{29}$ F within a three-body model
Jagjit Singh · J. Casal · W. Horiuchi · L. Fortunato · A. Vitturi
Background $:$ The $^{29}$ F system is located at the lower-N boundary of the "island of inversion" and is an exotic, weakly bound system. Little is known about this system beyond its two-neutron separation energy ( $S_{2 n}$ ) with large uncertainties. A similar situation is found for the low-lying spectrum of its unbound binary subsystem $^{28}$ F. Purpose $:$ To investigate the configuration mixing, matter radius and neutron-neutron correlations in the ground state of $^{29}$ F within a three-body model, exploring the possibility of $^{29}$ F to be a two-neutron halo nucleus. Method $:$ The $^{29}$ F ground-state wave function is built within the hyperspherical formalism by using an analytical transformed harmonic oscillator basis. The Gogny-Pires-Tourreil (GPT) nn interaction with central, spin-orbit and tensor terms is employed in the present calculations, together with different core $+ n$ potentials constrained by the available experimental information on $^{28}$ F. Results $:$ The $^{29}$ F ground-state configuration mixing and its matter radius are computed for different choices of the $^{28}$ F structure and $S_{2 n}$ value. The admixture of d-waves with pf components are found to play an important role, favoring the dominance of dineutron configurations in the wave function. Our computed radii show a mild sensitivity to the $^{27}$ F $+ n$ potential and $S_{2 n}$ values. The relative increase of the matter radius with respect to the $^{27}$ F core lies in the range 0.1-0.4 fm depending upon these choices. Conclusions $:$ Our three-body results for $^{29}$ F indicate the presence of a moderate halo structure in its ground state, which is enhanced by larger intruder components. This finding calls for an experimental confirmation.
Comments:
8 pages, 4 figures, Final version
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2001.01849 [pdf]
PRC(2020)·33 citations
02
[Submitted on 7 Jan 2020]
Interpretation of normal-deformed bands in 167Lu
Azam Kardan · Ingemar Ragnarsson · B. Gillis Carlsson · Hai-Liang Ma
With the aim to get a general understanding of rotational bands in the deformed rare-earth region or in deformed nuclei in general, the observed normal-deformed rotational structures in $^{167}$ Lu are interpreted within the unpaired and paired cranked Nilsson-Strutinsky formalisms, CNS and CNSB. Particular attention is devoted to the band crossings. For this nucleus with the Fermi surface high up in the $h_{11/2}$ shell, we conclude that except for the paired AB and BC crossings in configurations with an even and odd number of $i_{13/2}$ neutrons, respectively, the observed band crossings can be understood within the unpaired formalism. Especially, it means that above the AB and BC crossings, the evolution with spin is described as a gradual alignment of the spin vectors of the particles outside closed shells. Consequently, the configurations can be characterized by the number of particles occupying open $j$ -shells or groups of $j$ -shells. In the present study, we revise the interpretation of some experimental bands and also the nature of the crossings while some previous configuration assignments are confirmed.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2001.01922 [pdf]
PRC(2020)·8 citations
03
[Submitted on 7 Jan 2020]
PairDiag: an exact diagonalization program for solving general pairing Hamiltonians
Xiaoyu Liu · Chong Qi
We present a program for solving exactly the general pairing Hamiltonian based on diagonalization. The program generates the seniority-zero shell-model-like basis vectors via the `01' inversion algorithm. The Hamiltonian matrix is constructed in that seniority-zero space. The program evaluates all non-zero elements of the Hamiltonian matrix "on the fly" using the scattering operator and the search algorithm that act on the generated basis. The matrix is diagonalized by using the iterative Lanczos algorithm. The program thus developed, PairDiag, can calculate efficiently the ground-state eigenvalue and eigenvector of any pairing Hamiltonian. The program can be easily implemented to replace the BCS approximation in standard self-consistent mean-field calculations. The code is parallelized using OpenMP. For larger systems with dimension around 10 $^{8 - 9}$ , the calculation can be done within a day on standard desktop computers.
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
2001.01978 [pdf]
Comput.Phys.Commun.(2021)·8 citations
04
[Submitted on 7 Jan 2020]
Fission rate of excited nuclei at variable friction in the energy diffusion regime
Maria Chushnyakova · Igor Gontchar
Presently, it is well established that fission of excited nuclei is a dynamical process being a subject of fluctuations and dissipation. In the literature, there are indications that, at the compact nucleus shapes, the strength of nuclear friction is significantly reduced in comparison with the prediction of the one-body approach. Thus, one can expect that at small deformations the nuclear fission process occurs in the so-called "energy diffusion regime". The purpose of our present work is to compare an approximate analytical formula for the fission rate in this regime with the quasistationary numerical rate which is exact within the statistical errors. Our calculations demonstrate relatively good agreement between these two rates provided the friction parameter is deformation independent. If one accounts for its deformation dependence, the agreement becomes significantly poorer.
Comments:
INPC2019 contribution
Subjects:
Nuclear Theory (nucl-th); physics.chem-ph (physics.chem-ph)
arXiv:
2001.02051 [pdf]
J.Phys.Conf.Ser.(2020)·0 citations
05
[Submitted on 7 Jan 2020]
Two ways for numerical solution of the Kramers problem for spatial diffusion over an edge-shaped barrier
Maria Chushnyakova · Igor Gontchar · Alexander Zakharov · Natalya Khmyrova
Thermal decay rate over an edge-shaped barrier at high dissipation is studied numerically through the computer modeling. Two sorts of the stochastic Langevin type equations are applied: (i) the Langevin equations for the coordinate and conjugate momentum (LEqp, the phase space diffusion) and (ii) the reduced Langevin equation (RLE, the spatial diffusion, overdamped motion). The latter method is much faster and self-similar; however, one can doubt about its applicability in the case of an edge-shaped barrier with a discontinuous force. The reason is that a formal condition of the applicability of the RLE is not fulfilled since the curvature of the potential profile at the barrier is equal to infinity. The present numerical study demonstrates that, for large friction, the decay rate calculated using the RLE agrees with the rate resulting from the more exact LEqp. Moreover, it turns out that the influence of the position of the absorbing border is similar to the case of harmonic potential known in the literature.
Comments:
Dynamics-2019 Second contribution
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2001.02080 [pdf]
J.Phys.Conf.Ser.(2020)·0 citations
06
[Submitted on 7 Jan 2020]
Accuracy of the analytical escape rate for a cusp barrier in the overdamping regime
Alexander Zakharov · Maria Chushnyakova · Igor Gontchar
For the first time, the accuracy of the approximate analytical Kramers formula for the thermal decay rate over a cusp barrier, $R_{K}$ , is checked numerically for the overdamping regime. The numerical quasistationary rate, $R_{D}$ , which is believed to be exact within the statistical errors is evaluated by means of computer modeling of the stochastic Langevin-type dynamical equations. The agreement between $R_{K}$ and $R_{D}$ significantly depends upon the friction strength and the height of the barrier in comparison to the thermal energy. The difference between $R_{K}$ and $R_{D}$ decreases with the dimensionless damping parameter $ϕ$ , however, does not become smaller than 10-20%. The unexpected growth of the difference between $R_{K}$ and $R_{D}$ with the governing parameter is observed.
Comments:
Dynamics-2019 First contribution
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2001.02087 [pdf]
J.Phys.Conf.Ser.(2020)·0 citations
07
[Submitted on 7 Jan 2020]
Frame dependence of transition form factors in light-front dynamics
Meijian Li🇺🇸
We study the radiative transitions between vector and pseudoscalar quarkonia in the light-front Hamiltonian approach, and investigate the effects of using different current component and different reference frames. In practical calculations with truncated Fock spaces, transition form factors may acquire current component dependence and frame dependence, and such dependences could serve as a measure for the Lorentz symmetry violation. We suggest using the transverse current with $m_{j} = 0$ state of the vector meson, since this procedure employs the dominant spin components of the light-front wavefunctions and is more robust in practical calculations. We calculate the transition form factor between vector and pseudoscalar quarkonia and investigate the frame dependence with light-front wavefunctions calculated from the valence Fock sector. We suggest using frames with minimal longitudinal momentum transfer for calculations in the valence Fock sector, namely the Drell-Yan frame for the space-like region and a specific longitudinal frame for the timelike region; at $q^{2} = 0$ these two frames give the same result.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2001.02108 [pdf]
PoS(2020)·3 citations
08
[Submitted on 7 Jan 2020]
Strangeness and light fragment production at high baryon density
D. Blaschke🇵🇱 · G. Röpke🇷🇺 · Yu. Ivanov🇷🇺 · M. Kozhevnikova🇷🇺 · S. Liebing🇩🇪
We discuss medium effects on light cluster production in the QCD phase diagram within a generalized Beth-Uhlenbeck (GBU) approach by relating Mott transition lines to those for chemical freeze-out. We find that in heavy-ion collisions at highest energies provided by the LHC light cluster abundances should follow the statistical model because of low baryon densities. At low energies in the nuclear fragmentation region, where the freeze-out interferes with the liquid-gas phase transition, selfenergy and Pauli blocking effects are important. At intermediate energies the HADES, FAIR and NICA experiments can give new information. The GBU approach provides new insights to strange hadron production in this energy domain for explaining the "horn" effects.
Comments:
8 pages, 5 figures, Contribution to the Proceedings of the 18th International Conference on 'Strangeness in Quark Matter' (SQM-2019), Bari, Italy, 10-15 June, 2019
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2001.02156 [pdf]
Springer Proc.Phys.(2020)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE