Nuclear Theory·nucl-th

Tuesday·July 6, 2021

10 papers—4 primary·6 cross-listed

01
[Submitted on 3 Jul 2021]
Novel Neutron Star Structures with Nucleon Mass Radius
Wei Kou🇨🇳 · Xiaopeng Wang🇨🇳 · Xurong Chen🇨🇳
In order to reveal the difference between the latest neutron star observation experiment GW170817 and the existing theory, we mainly consider the effect of the nucleon radius on the neutron star from the existing theory. We believe that the effect of nucleon radius in neutron star is not negligible, and the mass radius of nucleon should be used instead of the charge radius. The nucleon mass radius is set as $r_{m} = 0.55 \pm 0.09$ fm from the new measurements. It is considered as an input to the "Excluded Volume Effects" model in the equation of state of nuclear matter. We propose a novel neutron star mass-radius relation by using proton mass radius is consistent with the observation GW170817.
Comments:
6 pages, 1 table, 2 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2107.01441 [pdf]
0 citations
02
[Submitted on 3 Jul 2021]
Electromagnetic field evolution in relativistic heavy-ion collision and its effect on flow of particles
Tewodros Gezhagn🇪🇹 · A. K. Chaubey🇪🇹
We compute the electromagnetic fields generated in relativistic heavy-ion collisions using the iEBE-VISHNU framework. We calculated the incremental drift velocity from the possible four sources of the electric force (coulomb, Lorentz, Faraday, and Plasma-based) on the particles created. The effect of this external electromagnetic field on the flow harmonics of particles was investigated, and we found out that the flow harmonics values get suppressed and rouse in a non-uniform fashion throughout the evolution. More precisely, a maximum of close to three percent increase in elliptic flow was observed. We also found mass more dominant factor than charges for the change in flow harmonics due to the created electromagnetic field. On the top of that, the magnetic field perpendicular to the reaction plane is found to be sizable while the different radial electric forces were found to cancel out each other. Finally, we found out that the inclusion of an electromagnetic field affects the flow of particles by suppressing or rising it in a non-uniform fashion throughout the evolution.
Comments:
9 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2107.01467 [pdf]
Front.in Phys.(2022)·4 citations
03
[Submitted on 3 Jul 2021]
Machine learning approach to pattern recognition in nuclear dynamics from the ab initio symmetry-adapted no-core shell model
O. M. Molchanov · K. D. Launey · A. Mercenne · G. H. Sargsyan · T. Dytrych · J. P. Draayer
A novel machine learning approach is used to provide further insight into atomic nuclei and to detect orderly patterns amidst a vast data of large-scale calculations. The method utilizes a neural network that is trained on ab initio results from the symmetry-adapted no-core shell model (SA-NCSM) for light nuclei. We show that the SA-NCSM, which expands ab initio applications up to medium-mass nuclei by using dominant symmetries of nuclear dynamics, can reach heavier nuclei when coupled with the machine learning approach. In particular, we find that a neural network trained on probability amplitudes for $s$ -and $p$ -shell nuclear wave functions not only predicts dominant configurations for heavier nuclei but in addition, when tested for the $^{20}$ Ne ground state, it accurately reproduces the probability distribution. The nonnegligible configurations predicted by the network provide an important input to the SA-NCSM for reducing ultra-large model spaces to manageable sizes that can be, in turn, utilized in SA-NCSM calculations to obtain accurate observables. The neural network is capable of describing nuclear deformation and is used to track the shape evolution along the $^{20 - 42}$ Mg isotopic chain, suggesting a shape-coexistence that is more pronounced toward the very neutron-rich isotopes. We provide first descriptions of the structure and deformation of $^{24}$ Si and $^{40}$ Mg of interest to x-ray burst nucleosynthesis, and even of the extremely heavy nuclei such as $^{166, 168}$ Er and $^{236}$ U, that build upon first principles considerations.
Comments:
10 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2107.01498 [pdf]
PRC(2022)·17 citations
04
[Submitted on 5 Jul 2021]
Cusp in the Symmetry Energy, Speed of Sound in Neutron Stars and Emergent Pseudo-Conformal Symmetry
Hyun Kyu Lee🇰🇷 · Yong-Liang Ma🇨🇳 · Won-Gi Paeng🇰🇵 · Mannque Rho🇫🇷
We review how the "cusp" predicted in the nuclear symmetry energy generated by a topology change at density $n_{1/2} \gsim 2 n_{0}$ can have a surprising consequence, so far unrecognized in nuclear physics and astrophysics communities, on the structure of dense compact-star matter. The topology change, when translated into nuclear EFT with "effective" QCD degrees of freedom in terms of hidden local and scale symmetries duly taken into account, predicts an EoS that is soft below and stiff above $n \gsim n_{1/2}$ , involving no low-order phase transitions, and yields the macrophysical properties of neutron stars consistent -- so far with no tension -- with the astrophysical observations, including the maximum mass $2.0 \lsim M / M_{⊙} \lsim 2.2$ as well as the GW data. Furthermore it describes the interior core of the massive stars populated by baryon-charge-fractionalized quasi-fermions that are neither baryonic nor quarkonic. It is argued that the cusp "buried" in the symmetry energy resulting from strong correlations with hidden heavy degrees of freedom leads, at $n \gsim n_{1/2}$ , to what we dubbed "pseudo-conformal" sound speed, $v_{p cs}^{2} / c^{2} \approx 1/3$ , precociously converged from below at $n_{1/2}$ . It is not strictly conformal since the trace of energy-momentum tensor is not zero even in the chiral limit. This observation with the topology change identified with the putative hadron-quark continuity, taking place at at density $\gsim 2 n_{0}$ , implies that the quantities accurately measured at $\sim n_{0}$ cannot give a stringent constraint for what takes place at the core density of compact stars $\sim (3 - 7) n_{0}$ . This is because the change of degrees of freedom in effective field theory is involved. We discuss the implication of this on the recent PREX-II "dilemma" in the measured skin thickness of $^{208}$ Pb.
Comments:
Invited review with title change in Modern Physics Letters A
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2107.01879 [pdf]
Mod.Phys.Lett.A(2022)·36 citations

Affiliations

first authorsco-authorsvia INSPIRE

Novel Neutron Star Structures with Nucleon Mass Radius

Electromagnetic field evolution in relativistic heavy-ion collision and its effect on flow of particles

Machine learning approach to pattern recognition in nuclear dynamics from the ab initio symmetry-adapted no-core shell model

Cusp in the Symmetry Energy, Speed of Sound in Neutron Stars and Emergent Pseudo-Conformal Symmetry

Affiliations