Nuclear Theory·nucl-th

Wednesday·March 31, 2021

9 papers—6 primary·3 cross-listed

01
[Submitted on 29 Mar 2021]
Low energy physics of interacting bosons with a moat spectrum, and the implications for condensed matter and cold nuclear matter
Robert D. Pisarski🇺🇸 · Alexei M. Tsvelik🇺🇸
We discuss bosonic models with a moat spectrum, where in momentum space the minimum of the dispersion relation is on a sphere of nonzero radius. For spinless bosons with $O (N)$ symmetry, we emphasize the essential difference between $N = 2$ and $N > 2$ . When $N = 2$ , there are two phase transitions: at zero temperature, a transition to a state with Bose condensation, and at nonzero temperature, a transition to a spatially inhomogeneous state. When $N > 2$ , previous analysis suggests that a mass gap is generated dynamically at any temperature. In condensed matter, a moat spectrum is important for spin-orbit-coupled bosons. For cold nuclear or quarkyonic matter, we suggest that the transport properties, such as neutrino emission, are dominated by the phonons related to a moat spectrum; also, that at least in the quarkyonic phase the nucleons may be a non-Fermi liquid.
Comments:
Superceded by the results in arXiv:2112.10238, with M. Lajer and R. Konik
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2103.15835 [pdf]
11 citations
02
[Submitted on 29 Mar 2021]
Models of breakup: a final state interaction problem. In memory of Mahir Hussein
Angela bonaccorso🇮🇹 · David M. Brink🇬🇧
In this paper we discuss the evolution of breakup models from fully quantum mechanical, such as the Ichimura-Austern-Vincent model to semiclassical, to eikonal approximations following the insight on the mechanism first proposed by Hussein and McVoy (HM) for the presently called stripping term. In particular we concentrate on, and stress that, the correct implementation of a quantum mechanical model of breakup requires the use of energy dependent interactions and the energy averaging procedure is a key point to understand the difference among models. On the other hand using fixed energy potentials is one of the steps towards the high energy eikonal limit first proposed by HM. However the intermediate semiclassical transfer to the continuum model (STC) of Bonaccorso and Brink does use an energy dependent nucleon-target optical potential, while fixing the core-target interaction at the incident energy. The relationship between these methods is clarified.
Comments:
38 pages, 4 figures, accepted for publication on the Eur. Phys. J. A, special issue "Cluster Structure and Dynamics of Nuclei - A Tribute to Mahir Hussein"
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.15866 [pdf]
EPJA(2021)·5 citations
03
[Submitted on 29 Mar 2021]
Causality violations in realistic simulations of heavy-ion collisions
Christopher Plumberg🇺🇸 · Dekrayat Almaalol🇺🇸 · Travis Dore🇺🇸 · Jorge Noronha🇺🇸 · Jacquelyn Noronha-Hostler🇺🇸
Causality is violated in the early stages of state-of-the-art heavy-ion hydrodynamic simulations. Such violations are present in up to 75% of the fluid cells in the initial time and only after 2-3 fm/ $c$ of evolution do we find that 50% of the fluid cells are definitely causal. Superluminal propagation reaches up to 15% the speed of light in some of the fluid cells. The inclusion of pre-equilibrium evolution significantly reduces the number of acausal cells. Our findings suggests that relativistic causality may place constraints on the available parameter space of heavy-ion collision simulations when factored into more thorough statistical analyses.
Comments:
v1 - 7 pages, 3 Figures, 1 Table, 102 References; v2 - 13 pages, 7 Figures, 1 Table, 108 References, 1 Appendix (as Supplemental Material); version published in Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2103.15889 [pdf]
PRC(2022)·76 citations
04
[Submitted on 30 Mar 2021]
Isovector spin susceptibility: Isotopic evolution of collectivity in spin response
Kenichi Yoshida🇯🇵
Background: Response to spin-dependent operators has been investigated in the magnetic dipole and Gamow-Teller transitions, which provides magnetic properties of a nuclear system. Purpose: I investigate an isotopic dependence of the collectivity generated by the spin-dependent interactions in the Ca and Ni isotopes through the isovector (IV) spin-flip excitations. The responses in the neutral $(t_{z})$ and charge-exchange $(t_{\pm})$ channels are considered in a unified way. Method: A nuclear energy-density functional approach is employed for calculating the response functions based on the Skyrme-Kohn-Sham-Bogoliubov method and the quasiparticle-random-phase approximation (QRPA). I adopt the like-particle QRPA and the proton-neutron QRPA for the neutral and charge-exchange channels, respectively. I consider the fluctuation of the proton-neutron pair fields. Results: The collective shift due to RPA correlations for the response in the neutral channel is explained by the occupation probability of neutrons in the $j_{>} = ℓ + 1/2$ orbital. Many particle-hole or two-quasiparticle excitations have a coherent contribution to form a giant resonance in neutron-rich nuclei for the charge-exchange channel. The IV spin susceptibility displays the isotopic evolution of the collectivity and the underlying shell structure. Conclusions: A repulsive character of the residual interaction in the spin-isospin channel diminishes the IV spin susceptibility due to the collectivity, while the dynamic $^{3} S$ pairing appearing in the charge-exchange channel opposes the reduction.
Comments:
Revised version and accepted to PRC; comparison with available experimental data, numerical results, and discussion were added
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.16119 [pdf]
PRC(2021)·4 citations
05
[Submitted on 30 Mar 2021]
KIDS density functional for deformed nuclei: Examples of the even-even Nd isotopes
Hana Gil🇰🇷 · Nobuo Hinohara🇯🇵 · Chang Ho Hyun🇰🇷 · Kenichi Yoshida🇯🇵
Background: A global description of the ground-state properties of nuclei in a wide mass range in a unified manner is desirable not only for understanding exotic nuclei but for providing nuclear data for applications. Purpose: We demonstrate the KIDS functional describes the ground states appropriately with respect to the existing data and predictions for a possible application of the functional to all the nuclei by taking Nd isotopes as examples. Method: The Kohn-Sham-Bogoliubov equation is solved for the Nd isotopes with the neutron numbers ranging from 60 to 160 by employing the KIDS functionals constructed to satisfy both neutron-matter equation of state or neutron star observation and selected nuclear data. Results: Considering the nuclear deformation improves the description of the binding energies and radii. We find that the discrepancy from the experimental data is more significant for neutron-rich/deficient isotopes and this can be made isotope independent by changing the slope parameter of the symmetry energy. Conclusions: The KIDS functional is applied to the mid-shell nuclei for the first time. The onset and evolution of deformation are nicely described for the Nd isotopes. The KIDS functional is competent to a global fitting for a better description of nuclear properties in the nuclear chart.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.16135 [pdf]
J.Korean Phys.Soc.(2022)·7 citations
06
[Submitted on 30 Mar 2021]
Semiclassical shell-structure micro-macroscopic approach for the level density
A.G. Magner🇺🇦 · A.I. Sanzhur🇺🇦 · S.N. Fedotkin🇺🇦 · A.I. Levon🇺🇦 · S. Shlomo🇺🇸
Level density $ρ (E, A)$ is derived for a one-component nucleon system with a given energy $E$ and particle number $A$ within the mean-field semiclassical periodic-orbit theory beyond the saddle-point method of the Fermi gas model. We obtain $ρ \propto I_{ν} (S) / S^{ν}$ , with $I_{ν} (S)$ being the modified Bessel function of the entropy $S$ . Within the micro-macro-canonical approximation (MMA), for a small thermal excitation energy, $U$ , with respect to rotational excitations, $E_{rot}$ , one obtains $ν = 3/2$ for $ρ (E, A)$ . In the case of excitation energy $U$ larger than $E_{rot}$ but smaller than the neutron separation energy, one finds a larger value of $ν = 5/2$ . A role of the fixed spin variables for rotating nuclei is discussed. The MMA level density $ρ$ reaches the well-known grand-canonical ensemble limit (Fermi gas asymptotic) for large $S$ related to large excitation energies, and also reaches the finite micro-canonical limit for small combinatorial entropy $S$ at low excitation energies (the constant "temperature" model). Fitting the $ρ (E, A)$ of the MMA to the experimental data for low excitation energies, taking into account shell and, qualitatively, pairing effects, one obtains for the inverse level density parameter $K$ a value which differs essentially from that parameter derived from data on neutron resonances.
Comments:
21 pages, 4 figures, 1 Table
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.16480 [pdf]
PRC(2021)·9 citations
07
[Submitted on 29 Mar 2021] (cross-list from hep-ph)
The role of $U (1)_{A}$ symmetry breaking in the QCD corrections to the pion mass difference
Mahammad Sabir Ali🇮🇳 · Chowdhury Aminul Islam🇨🇳 · Rishi Sharma🇮🇳
The charged and neutral pion mass difference can be attributed to both the QED and QCD contributions. The current quark mass difference ( $Δ m$ ) is the source of the QCD contribution. Here, in a two-flavour non-local NJL model, we try to estimate the QCD contribution. Interestingly, we find that the strength of the $U (1)_{A}$ symmetry-breaking parameter $c$ plays a crucial role in obtaining the pion mass difference while intertwined with the current quark mass difference. To obtain the QCD contribution for the pion mass difference, we scan the parameter space in ${Δ m, c}$ , and by comparing this with the existing results, we constrained the parameter space. Further, using a fitted value of $c$ , we determine the allowed range for the $Δ m$ in the model. The model estimated $Δ m$ ranges enable us to extract the chiral perturbation theory low-energy constant, $l_{7}$ and verify the dependence of the pion mass difference on $Δ m$ . We also find out its dependence on $c$ \textemdash\, it increases with the decreasing value of $c$ , i.e., toward an axial anomaly restored phase.
Comments:
12 pages, 6 captioned figures, discussion on l7 has been added, accepted in JPG
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2103.15849 [pdf]
J.Phys.G(2023)·7 citations
08
[Submitted on 29 Mar 2021] (cross-list from hep-ph)
Constraining the strength of $U (1)_{A}$ symmetry breaking using 2-flavour non-local NJL model
Mahammad Sabir Ali🇮🇳 · Chowdhury Aminul Islam🇨🇳 · Rishi Sharma🇮🇳
In presence of magnetic field we have done a systematic analysis to constrain the strength of 't Hooft determinant term using LQCD data within a non-local version of two flavour NJL model. Topological susceptibility, being related to the axial symmetry, have also been calculated and compared with LQCD results to further validate our calculation.
Comments:
Proceedings of the contributory talk at XXIV DAE-BNRS High Energy Physics Symposium 2020 held at NISER, Bhubaneswar, Odisha
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2103.15883 [pdf]
Springer Proc.Phys.(2022)·1 citation
09
[Submitted on 29 Mar 2021] (cross-list from hep-ph)
Heavy+light pseudoscalar meson semileptonic transitions
Zhen-Ni Xu🇨🇳 · Zhu-Fang Cui🇨🇳 · Craig D. Roberts🇨🇳 · Chang Xu🇨🇳
A symmetry-preserving regularisation of a vector $\times$ vector contact interaction (SCI) is used to deliver a unified treatment of semileptonic transitions involving $π$ , $K$ , $D_{(s)}$ , $B_{(s, c)}$ initial states. The framework is characterised by algebraic simplicity, few parameters, and the ability to simultaneously treat systems from Nambu-Goldstone modes to heavy+heavy mesons. Although the SCI form factors are typically somewhat stiff, the results are comparable with experiment and rigorous theory results. Hence, predictions for the five unmeasured $B_{s, c}$ branching fractions should be a reasonable guide. The analysis provides insights into the effects of Higgs boson couplings via current-quark masses on the transition form factors; and results on $B_{(s)} \to D_{(s)}$ transitions yield a prediction for the Isgur-Wise function in fair agreement with contemporary data.
Comments:
17 pages, 13 figures, 3 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2103.15964 [pdf]
EPJC(2021)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE