Nuclear Theory·nucl-th

Tuesday·June 30, 2020

21 papers—12 primary·9 cross-listed

01
[Submitted on 26 Jun 2020]
Initial fluctuations and power spectrum of flow anisotropies in relativistic heavy-ion collisions
Shreyansh S. Dave🇮🇳 · Saumia P.S.🇷🇺 · Ajit M. Srivastava🇮🇳
Flow has emerged as a crucial probe for the properties of the thermalized medium produced in relativistic heavy-ion collisions. The evolution of initial state fluctuations leaves imprints on the power spectrum of flow coefficients. Therefore flow coefficients are a crucial probe of initial state fluctuations arising from the parton distributions of the colliding nuclei. This has a very strong correspondence with the physics of power spectrum of cosmic microwave background radiation (CMBR) anisotropies which directly probes initial inflationary fluctuations. Much work has been done to probe these interesting interconnections, in particular, in developing techniques for the measurements of higher flow coefficients. We present a short review of these developments. The effect of initial magnetic field on these features will also be reviewed. All this acquires special importance in view of upcoming electron-ion collider which will directly probe initial parton distribution of the colliding nucleus.
Comments:
31 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2006.15177 [pdf]
Eur.Phys.J.ST(2021)·2 citations
02
[Submitted on 26 Jun 2020]
A shell-model study of calcium isotopes towards their drip line
L. Coraggio · G. De Gregorio · A. Gargano · N. Itaco · T. Fukui · Y. Z. Ma · F. R. Xu
We report in this paper a study in terms of the nuclear shell model about the location of the calcium isotopes drip line. The starting point is considering the realistic two-body potential derived by Entem and Machleidt within chiral perturbation theory at next-to-next-to-next-to-leading order (N3LO), as well as a chiral three-body force at next-to-next-to-leading order (N2LO) whose structure and low-energy constants are consistent with the two-body potential. Then we construct the effective single-particle energies and residual interaction needed to diagonalize the shell-model Hamiltonian. The calculated two-neutron separation energies agree nicely with experiment until 56Ca, which is the heaviest isotope whose mass has been measured, and do not show any sign of two-neutron emission until 70Ca. We discuss the role of the choice of the model space in determining the neutron drip line, and also the dependence of the results on the parameters of the shell-model Hamiltonian.
Comments:
9 pages, 9 figures, 3 tables, to be published in Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.15196 [pdf]
PRC(2020)·26 citations
03
[Submitted on 27 Jun 2020]
Entrainment effects in neutron-proton mixtures within the nuclear-energy density functional theory. II. Finite temperatures and arbitrary currents
Valentin Allard · Nicolas Chamel
Mutual entrainment effects in hot neutron-proton superfluid mixtures are studied in the framework of the self-consistent nuclear energy-density functional theory. The local mass currents in homogeneous or inhomogeneous nuclear systems, which we derive from the time-dependent Hartree-Fock-Bogoliubov equations at finite temperatures, are shown to have the same formal expression as the ones we found earlier in the absence of pairing at zero temperature. Analytical expressions for the entrainment matrix are obtained for application to superfluid neutron-star cores. Results are compared to those obtained earlier using Landau's theory. Our formulas, valid for arbitrary temperatures and currents, are applicable to various types of functionals including the Brussels-Montreal series for which unified equations of state have been already calculated, thus laying the ground for a fully consistent microscopic description of superfluid neutron stars.
Comments:
23 pages, expanded version including the exact solution of TDHFB. Accepted for publication in Physical Review C
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2006.15317 [pdf]
PRC(2021)·12 citations
04
[Submitted on 27 Jun 2020]
Precision determination of pion-nucleon coupling constants using effective field theory
P. Reinert🇩🇪 · H. Krebs🇩🇪 · E. Epelbaum🇩🇪
The pion-nucleon coupling constants determine the strength of the long-range nuclear forces and play a fundamental part in our understanding of nuclear physics. While the charged- and neutral-pion couplings to protons and neutrons are expected to be very similar, owing to the approximate isospin symmetry of the strong interaction, the different masses of the up- and down-quarks and electromagnetic effects may result in their slightly different values. Despite previous attempts to extract these coupling constants from different systems, our knowledge of their values is still deficient. In this Letter we present a precision determination of these fundamental observables with fully controlled uncertainties from neutron-proton and proton-proton scattering data using chiral effective field theory. To achieve this goal, we use a novel methodology based on the Bayesian approach and perform, for the first time, a full-fledged partial-wave analysis of nucleon-nucleon scattering up to the pion production threshold in the framework of chiral effective field theory, including a complete treatment of isospin-breaking effects and our own determination of mutually consistent data. The resulting values of the pion-nucleon coupling constants are accurate at the percent level and show no significant charge dependence. These results mark an important step towards developing a precision theory of nuclear forces and structure.
Comments:
15 pages (including Supplementary Material), 5 figures, 5 tables. Version published in Physical Review Letters
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2006.15360 [pdf]
PRL(2021)·67 citations
05
[Submitted on 27 Jun 2020]
Constraints from GW170817 on the bulk viscosity of neutron star matter and the r-mode instability
T. R. Routray🇮🇳 · S. P. Pattnaik🇮🇳 · C. Gonzalez-Boquera🇪🇸 · X. Viñas🇪🇸 · M. Centelles🇪🇸 · B. Behera🇮🇳
We perform a systematic study of the dependence of the r-mode phenomenology in normal fluid pulsar neutron stars on the symmetry energy slope parameter $L$ . An essential ingredient in this study is the bulk viscosity, which is evaluated consistently for several equations of state corresponding to different values of the slope parameter $L$ . Direct Urca processes, which are allowed from a critical $L$ -value onwards, enhance the bulk viscosity and have large influence on the $r$ -mode features, such as the instability boundary and spin-down properties of newborn neutron stars. The magnitude of the changes in the $r$ -mode properties induced by the direct Urca processes are driven by the $L$ -value of the equation of state and the mass of the pulsar. The study has been done by using a family of equations of state of $β$ -equilibrated neutron star matter obtained with the finite range simple effective interaction, which provides realistic results for nuclear matter and finite nuclei properties. These equations of state predict the same properties in symmetric nuclear matter and have the same value of the symmetry energy parameter, $E_{s} (ρ_{0})$ , but differ in the slope parameter $L$ . The range chosen for the variation of $L$ is decided from the tidal deformability data extracted from the GW170817 event and the maximum mass constraint.
Comments:
48 pages, 19 figures, 5 tables
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
2006.15430 [pdf]
5 citations
06
[Submitted on 28 Jun 2020]
Conformal Symmetry in nuclear structure
Panagioti E Georgoudis🇫🇷
The purpose of this paper is to introduce the unitary limit as applied in systems of cold atoms into collective states of heavy, even-even nuclei and to identify a related physical example. This is accompanied by the determination of observables of conformal symmetry in nuclear structure. A Hamiltonian is defined that governs the scattering process of an incident pair of two slow neutrons onto a heavy, even-even target nucleus in the framework of the Interacting Boson Model of nuclear structure. A unitary pair-collective state interaction is introduced along with the effective range expansion of a pair-collective state scattering length. The solutions to the coupled channels equations provide a scattering state for the two neutrons that couples with intermediate states of the $A + 2 n$ compound nucleus. The unitary limit manifests itself when the intermediate states correspond to pair-collective state resonances the positions of which coincide with the energies of IBM states of the closed channels. The position and the width of each resonance is measurable via the fluctuation of the cross section which tunes the pair-collective state scattering length. Conformal symmetry is represented in a tower of equally spaced states that emerges at the unitary limit from two-boson excitations on the IBM state of the closed channel. These tower states are experimentally testable as a regularity pattern of fluctuations of the cross section, in terms of regular positions and widths. The manifestation of the unitary limit and conformal symmetry via fluctuations of the cross section indicates the $A + 2 n$ compound nucleus as a physical laboratory for the examination of the BCS-BEC crossover, of an underlying critical point and of algebras with infinite number of generators.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2006.15508 [pdf]
NPA(2021)·4 citations
07
[Submitted on 28 Jun 2020]
Medium effects on $Ξ^{-}$ production in the nuclear ( $K^{-}$ , $K^{+}$ ) reaction
Toru Harada🇯🇵 · Yoshiharu Hirabayashi🇯🇵
We study theoretically medium effects on $Ξ^{-}$ production in the ( $K^{-}$ , $K^{+}$ ) reaction, using the optimal Fermi-averaging procedure which describes the Fermi motion of a nucleon on the on-energy-shell $K^{-} p \to K^{+} Ξ^{-}$ reaction condition in nuclei. The result shows the strong energy and angular dependence of the in-medium $K^{-} p \to K^{+} Ξ^{-}$ cross section,which affects significantly the shape and magnitude of the production spectrum for $Ξ^{-}$ hypernuclear states in the ( $K^{-}$ , $K^{+}$ ) reaction on a nuclear target.The application to the $Ξ^{-}$ quasi-free production via the ( $K^{-}$ , $K^{+}$ ) reaction on a $^{12}$ C target is also discussed in a Fermi gas model.
Comments:
18 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex)
arXiv:
2006.15627 [pdf]
PRC(2020)·4 citations
08
[Submitted on 28 Jun 2020]
Extending Standard Atomic Kernel Model with New Interpretation of Strong Forces
Dr Ing Hongguang Yang · Dr ret nat Weidong Yang
This paper gives an extended model of the atomic nucleus - we call it the YY model, which allows a new description for strong forces from the well-known Standard Model. The forces that hold the nucleus together (protons and neutrons) can be expressed in a new way. Based on the YY model, more structural description details for an atomic nucleus will be possible than is the case with the conventional description. The YY model is compatible with the standard model. However, it allows for very delicate considerations when modelling the distribution of protons and neutrons within or around an atomic nucleus. Furthermore, it can explain many subatomic processes in an elegant way. The YY model predicts some subatomic aspects that can be explored in a deeper step. Our approach also includes a native common root for the description of macrophysics (space, dark matter and cosmology). Following a model-driven approach - a methodology widely used in computer science and informatics - the investigations in this paper will completely dispense with mathematical formulations. In addition, energy balances in the transformations are left out. Many different aspects that can be derived from this new mechanism can then be verified. We hope to gain the confidence of many other physicists in the YY model. They could make detailed theoretical and experimental verifications by adding additional descriptive elements and linking the YY model to the known quantum field theories and the widely accepted big bang theories for space and cosmology, especially for research on dark matter.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2006.15695 [pdf]
0 citations
09
[Submitted on 28 Jun 2020]
Observable signatures of initial state momentum anisotropies in nuclear collisions
Giuliano Giacalone🇫🇷 · Bjoern Schenke🇺🇸 · Chun Shen🇺🇸
We show that the correlation between the elliptic momentum anisotropy, $v_{2}$ , and the average transverse momentum, $[p_{T}]$ , at fixed multiplicity in small system nuclear collisions carries information on the origin of the observed momentum anisotropy. A calculation using a hybrid IP-Glasma+\textsc{Music}+UrQMD model that includes contributions from final state response to the initial geometry as well as initial state momentum anisotropies of the Color Glass Condensate, predicts a characteristic sign change of the correlator $ρ^(v_{2}^{2}, [p_{T}])$ as a function of charged particle multiplicity in p+Au and d+Au collisions at $s = 200 GeV$ , and p+Pb collisions at $s = 5.02 TeV$ . This sign change is absent in calculations without initial state momentum anisotropies. The model further predicts a qualitative difference between the centrality dependence of $ρ^(v_{2}^{2}, [p_{T}])$ in Au+Au collisions at $s = 200 GeV$ and Pb+Pb collisions at $s = 5.02 TeV$ , with only the latter showing a sign change in peripheral events. Predictions for O+O collisions at different collision energy show a similar behavior. Experimental observation of these distinct qualitative features of $ρ^(v_{2}^{2}, [p_{T}])$ in small and large systems would constitute strong evidence for the presence and importance of initial state momentum anisotropies predicted by the Color Glass Condensate effective theory.
Comments:
6 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2006.15721 [pdf]
PRL(2020)·72 citations
10
[Submitted on 29 Jun 2020]
Insights on pion production mechanism and symmetry energy at high density
Yangyang Liu🇨🇳 · Yongjia Wang🇨🇳 · Ying Cui🇨🇳 · Chen-Jun Xia🇨🇳 · Zhuxia Li🇨🇳 · Yongjing Chen🇨🇳 · Qingfeng Li🇨🇳 · Yingxun Zhang🇨🇳
The $N Δ \to N N$ cross sections, which take into account the $Δ$ -mass dependence of M-matrix and momentum $p_{N Δ}$ , are applied on the calculation of pion production within the framework of the UrQMD model. Our study shows that UrQMD calculations with the $Δ$ -mass dependent $N Δ \to N N$ cross sections enhance the pion multiplicities and decrease the $π^{-} / π^{+}$ ratios. By analyzing the time evolution of the pion production rate and the density in the overlapped region for Au+Au at the beam energy of 0.4A GeV, we find that the pion multiplicity probes the symmetry energy in the region of 1-2 times normal density. The process of pion production in the reaction is tracked including the loops of $N N \leftrightarrow N Δ$ and $Δ \leftrightarrow N π$ , our calculations show that the sensitivity of $π^{-} / π^{+}$ to symmetry energy is weakened after 4-5 N- $Δ$ - $π$ loops in the pion production path, while the $π^{-} / π^{+}$ ratio in reactions at near threshold energies remains its sensitivity to the symmetry energy. By comparing the calculations to the FOPI data, we obtain a model dependent conclusion on the symmetry energy and the symmetry energy at two times normal density is $S (2 ρ_{0})$ =38-73 MeV within $1 σ$ uncertainties. Under the constraints of tidal deformability and maximum mass of neutron star, the symmetry energy at two times normal density is reduced to $48 - 58$ MeV and slope of symmetry energy $L = 54 - 81$ MeV, and it is consistent with the constraints from ASY-EOS flow data.
Comments:
11 pages, 9 fiigures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2006.15861 [pdf]
PRC(2021)·42 citations
11
[Submitted on 29 Jun 2020]
Systematic Analysis of Flow Distributions
Hadi Mehrabpour🇮🇷
The information of the event-by-event fluctuations is extracted from flow harmonic distributions and cumulants, which can be done experimentally. In this work, we employ the standard method of Gram-Charlier series with the normal kernel to find such distribution, which is the generalization of recently introduced flow distributions for the studies of the event-by-event fluctuations. Also, we introduce a new set of cumulants $j_{n} {2 k}$ which have more information about the fluctuations compared with other known cumulants. The experimental data imply that not only all of the information about the event-by-event fluctuations of collision zone properties and different stages of the heavy-ion process are not encoded in the radial flow distribution $p (v_{n})$ , but also the observables describing harmonic flows can generally be given by the joint distribution $P (v_{1}, v_{2}, ...)$ . In such a way, we first introduce a set of joint cumulants $K_{nm}$ , and then we find the flow joint distribution using these joint cumulants. Finally, we show that the Symmetric Cumulants $S C (2, 3)$ and $S C (2, 4)$ obtained from ALICE data are explained by the combinations $K_{22} + \frac{1}{2} K_{04} - K_{31}$ and $K_{22} + 4 K_{11}^{2}$ .
Comments:
12 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2006.16019 [pdf]
PRC(2020)·5 citations
12
[Submitted on 29 Jun 2020]
Nucleon Polarizabilities and Compton Scattering as a Playground for Chiral Perturbation Theory
Franziska Hagelstein (AEC Bern)🇨🇭
I give a summary of recent results on nucleon polarizabilities, with emphasis on chiral perturbation theory. The predictive calculations of Compton scattering off the nucleon are compared to recent empirical determinations and lattice QCD calculations of the polarizabilities, thereby testing chiral perturbation theory in the single-baryon sector.
Comments:
23 pages, 13 figures, 1 table, published in "Symmetry" as invited article for the special issue on "Effective Field Theories - Chiral Perturbation Theory and Non-relativistic QFT"
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2006.16124 [pdf]
Symmetry(2020)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE