Nuclear Theory·nucl-th

Friday·June 28, 2019

10 papers—6 primary·4 cross-listed

01
[Submitted on 26 Jun 2019]
Application of the variational principle to a coherent-pair condensate: The HFB case
L. Y. Jia
Recently we proposed a scheme that applies the variational principle to a coherent-pair condensate in the BCS case [Phys. Rev. C 99, 014302 (2019)]. This work extends the scheme to the HFB case by allowing variation of the canonical single-particle basis. The result is equivalent to that of the so-called variation after particle-number projection in the HFB case, but now the particle number is always conserved and the time-consuming projection is avoided. Specifically, we derive the analytical expression for the gradient of the average energy with respect to changes of the canonical basis, which is then used in the family of gradient minimizers to iteratively minimize energy. In practice, we find the so-called ADAM minimizer (adaptive moments of gradient), borrowed from the machine-learning field, is very effective. The new algorithm is demonstrated in a semi-realistic example using the realistic $V_{low - k}$ interaction and large model spaces (up to $15$ harmonic-oscillator major shells). It easily runs on a laptop, and practically the computer time cost (in the HFB case) is several times that of solving HF by the gradient minimizers. We hope the new algorithm could become a common practice because of its simplicity.
Comments:
This paper is a sequel to "arXiv:1808.03729 [nucl-th] (2018)"
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.11244 [pdf]
Comput.Phys.Commun.(2020)·3 citations
02
[Submitted on 27 Jun 2019]
Importance of multicranked configuration mixing for angular-momentum-projection calculations: Study of superdeformed rotational bands in $^{152}$ Dy and $^{194}$ Hg
Masaki Ushitani · Shingo Tagami · Yoshifumi R. Shimizu
Recently we have investigated an effective method of multicranked configuration-mixing for angular-momentum-projection calculation, where several cranked mean-field states are coupled after projection: The basic idea was originally proposed by Peierls and Thouless more than fifty years ago. With this method a good description of the rotational band has been achieved in a fully microscopic manner. In the present work, we apply the method to the high-spin superdeformed band, for which long rotational sequence is observed, and study how the good description is obtained for the rotational spectrum as well as the $\Jonem$ and $\Jtwom$ moments of inertia as functions of angular momentum. The Gogny D1S force is employed as an effective interaction, and the yrast superdeformed bands in $^{152}$ Dy and $^{194}$ Hg are taken as typical examples in the $A \approx 150$ and $A \approx 190$ regions, respectively. The effect of pairing correlations is examined by the variation after particle-number projection approach to understand the different behaviors of $\Jtwom$ moments of inertia observed in these two nuclei. The particle-number projection on top of the angular-momentum projection has been performed for the first time with the multicranked configuration-mixing.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.11418 [pdf]
PRC(2019)·5 citations
03
[Submitted on 26 Jun 2019]
Sensitivity analysis of the chiral magnetic effect observables using a multiphase transport model
Ling Huang🇨🇳 · Mao-Wu Nie🇨🇳 · Guo-Liang Ma🇨🇳
Because the traditional observable of charge-dependent azimuthal correlator $γ$ contains both contributions from the chiral magnetic effect (CME) and its background, a new observable of $R_{Ψ_{m}}$ has been recently proposed which is expected to be able to distinguish the CME from the background. In this study, we apply two methods to calculate $R_{Ψ_{m}}$ using a multiphase transport model without or with introducing a percentage of CME-induced charge separation. We demonstrate that the shape of final $R_{Ψ_{2}}$ distribution is flat for the case without the CME, but concave for that with an amount of the CME, because the initial CME signal survives from strong final state interactions. By comparing the responses of $R_{Ψ_{2}}$ and $γ$ to the strength of the initial CME, we observe that two observables show different nonlinear sensitivities to the CME. We find that the shape of $R_{Ψ_{2}}$ has an advantage in measuring a small amount of the CME, although it requires large event statistics.
Comments:
9 pages, 7 figures, add Figure 7 and more details in subsection III B
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1906.11631 [pdf]
PRC(2020)·18 citations
04
[Submitted on 27 Jun 2019]
Hyperon-nucleon interaction within chiral effective field theory revisited
J. Haidenbauer🇩🇪 · U.-G. Meißner🇩🇪 · A. Nogga🇩🇪
The $Λ N$ and $Σ N$ interactions are considered at next-to-leading order in SU(3) chiral effective field theory. Different options for the low-energy constants that determine the strength of the contact interactions are explored. Two variants are analysed in detail which yield equivalent results for $Λ N$ and $Σ N$ scattering observables but differ in the strength of the $Λ N \to Σ N$ transition potential. The influence of this difference on predictions for light hypernuclei and on the properties of the $Λ$ and $Σ$ hyperons in nuclear matter is investigated and discussed. The effect of the variation in the potential strength of the $Λ N$ - $Σ N$ coupling (also called $Λ - Σ$ conversion) is found to be moderate for the considered $_{Λ}^{3} H$ and $_{Λ}^{4} He$ hypernuclei but sizable in case of the matter properties. Further, the size of three-body forces and their relation to different approaches to hypernuclear interactions is discussed.
Comments:
22 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.11681 [pdf]
EPJA(2020)·178 citations
05
[Submitted on 27 Jun 2019]
Impact of chiral hyperonic three-body forces on neutron stars
Domenico Logoteta · Isaac Vidana · Ignazio Bombaci
We study the effect of the nucleon-nucleon-lambda (NN $Λ$ ) three-body force on neutron stars. In particular, we consider the NN $Λ$ force recently derived by the Jülich--Bonn--Munich group within the framework of chiral effective field theory at next-to-next-to-leading order. This force, together with realistic nucleon-nucleon, nucleon-nucleon-nucleon and nucleon-hyperon interactions, is used to calculate the equation of state and the structure of neutron stars within the many-body non-relativistic Brueckner-Hartree-Fock approach. Our results show that the inclusion of the NN $Λ$ force leads to an equation of state stiff enough such that the resulting neutron star maximum mass is compatible with the largest currently measured ( $\sim 2 M_{⊙}$ ) neutron star masses. Using a perturbative many-body approach we calculate also the separation energy of the $Λ$ in some hypernuclei finding that the agreement with the experimental data improves for the heavier ones when the effect of the NN $Λ$ force is taken into account.
Comments:
7 pages, 5 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.11722 [pdf]
EPJA(2019)·87 citations
06
[Submitted on 27 Jun 2019]
Semiclassical origin of asymmetric nuclear fission: Nascent-fragment shell effect in periodic-orbit theory
K. Arita · T. Ichikawa · K. Matsuyanagi
The origin of the asymmetry in the fragment mass distribution of low-energy nuclear fission is considered from the semiclassical point of view. Using the semiclassical periodic-orbit theory, one can define and quantify the shell effect associated with spatially localized nascent-fragment (prefragment) part of the potential. We investigate the roles of prefragments in the deformed shell effect using a simple cavity potential model but with realistic shape degrees of freedom for describing the fission processes. The results suggest that the prefragment magic numbers play essential roles in determining the shapes at the fission saddles, which should have a close relation to the fragment mass distribution.
Comments:
Published version, 10 pages, 17 figures, focus issue on "Nuclear Shapes and Symmetries: from Experiment to Theory"
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1906.11794 [pdf]
Phys.Scripta(2020)·2 citations
07
[Submitted on 26 Jun 2019] (cross-list from hep-ph)
Critical behavior of the bulk viscosity in QCD
Mauricio Martinez🇺🇸 · Thomas Schaefer🇺🇸 · Vladimir Skokov🇺🇸
We study the behavior of the bulk viscosity $ζ$ in QCD near a possible critical endpoint in the phase diagram. We verify the expectation that $(ζ / s) \sim a (ξ / ξ_{0})^{x_{ζ}}$ , where $s$ is the entropy density, $ξ$ is the correlation length, $ξ_{0}$ is the non-critical correlation length, $a$ is a constant and $x_{ζ} ≃ 3$ . Using a recently developed equation of state that includes a critical point in the universality class of the Ising model we estimate the constant of proportionality $a$ . We find that $a$ is typically quite small, $a \sim O (1 0^{- 4})$ . We observe, however, that the result is sensitive to the commonly made assumption that the Ising temperature axis is approximately aligned with the QCD baryon chemical potential axis. If this is not the case, then the critical $ζ / s$ can approach the non-critical value of $η / s$ , where $η$ is the shear viscosity, even if the enhancement of the correlation length is modest, $ξ / ξ_{0} \sim 2$ .
Comments:
18 pages, 3 figures; version to appear in PRD
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.11306 [pdf]
PRD(2019)·48 citations
08
[Submitted on 27 Jun 2019] (cross-list from nucl-ex)
Experimental searches for the chiral magnetic effect in heavy-ion collisions
Jie Zhao🇺🇸 · Fuqiang Wang🇺🇸
The chiral magnetic effect (CME) in quantum chromodynamics (QCD) refers to a charge separation (an electric current) of chirality imbalanced quarks generated along an external strong magnetic field. The chirality imbalance results from interactions of quarks, under the approximate chiral symmetry restoration, with metastable local domains of gluon fields of non-zero topological charges out of QCD vacuum fluctuations. Those local domains violate the $P$ and $C P$ invariance, potentially offering a solution to the strong $C P$ problem in explaining the magnitude of the matter-antimatter asymmetry in today's universe. Relativistic heavy-ion collisions, with the likely creation of the high energy density quark-gluon plasma and restoration of the approximate chiral symmetry, and the possibly long-lived strong magnetic field, provide a unique opportunity to detect the CME. Early measurements of the CME-induced charge separation in heavy-ion collisions are dominated by physics backgrounds. Major efforts have been devoted to eliminate or reduce those backgrounds. We review those efforts, with a somewhat historical perspective, and focus on the recent innovative experimental undertakings in the search for the CME in heavy-ion collisions.
Comments:
Invited review by Progress in Particle and Nuclear Physics, 57 pages, 33 figures
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.11413 [pdf]
PPNP(2019)·123 citations
09
[Submitted on 27 Jun 2019] (cross-list from physics.atom-ph)
Theoretical study of $^{173}$ YbOH to search for the nuclear magnetic quadrupole moment
Daniel E. Maison🇷🇺 · Leonid V. Skripnikov🇷🇺 · Victor V. Flambaum🇦🇺
CP-violating interaction of the nuclear magnetic quadrupole moment (MQM) with electrons in the ytterbium mono-hydroxide molecule, $^{173}$ YbOH, is considered. Both the magnetic quadrupole moment (MQM) of the $^{173}$ Yb nucleus and the molecular interaction constant WM are estimated. Electron correlation effects are taken into account within the relativistic Fock-space coupled cluster method. Results are interpreted in terms of the strength constants of CP-violating nuclear forces, neutron EDM, QCD vacuum angle $θ$ , quark EDM and chromo-EDM.
Subjects:
Atomic Physics (physics.atom-ph); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.11487 [pdf]
PRA(2019)·47 citations
10
[Submitted on 27 Jun 2019] (cross-list from hep-ph)
A look at multiplicity distributions via modified combinants
M.Rybczynski🇵🇱 · Z.Wlodarczyk🇵🇱 · G.Wilk🇵🇱
The experimentally measured multiplicity distributions exhibit, after closer inspection, peculiarly enhanced void probability and oscillatory behavior of the modified combinants. We show that both these features can be used as additional sources of information, not yet fully explored, on the mechanism of multiparticle production. We provide their theoretical understanding within the class of compound distributions.
Comments:
Talk presented at the New Trends in HEP conference, Odessa, Ukraine, May 12-18. 2019; 6 pages, to be published in Ukrainian J. Phys. 2019
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1906.11531 [pdf]
Ukr.J.Phys.(2019)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE