Nuclear Theory·nucl-th

Monday·March 22, 2021

13 papers—9 primary·4 cross-listed

01
[Submitted on 18 Mar 2021]
Cluster dynamics studied with the phase-space Minimum Spanning Tree approach
Viktar Kireyeu🇷🇺
The origin of weakly bound objects like clusters and hypernuclei, observed in heavy-ion collisions, is of theoretical and experimental interest. It is in the focus of the experiments at RHIC and LHC since it is not evident how such weakly bound objects can survive in an environment whose hadronic decay products point to a temperature of the order of 150 MeV. It is as well one of the key research topics in the future facilities of FAIR and NICA which are under construction in Darmstadt (Germany) and Dubna (Russia), respectively. We present here first results on the cluster dynamics within the model-independent cluster recognition library "phase-space Minimum Spanning Tree" (psMST) applied to different transport approaches: PHQMD, PHSD, SMASH and UrQMD. The psMST is based on the "Minimum Spanning Tree" (MST) algorithm for the cluster recognition which exploits correlations in coordinate space, and it is extended to correlations of baryons in the clusters in momentum space. We show the sensitivity of the cluster formation on the microscopic realization of the n-body dynamics and on the potential interactions in heavy-ion collisions.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex)
arXiv:
2103.10542 [pdf]
PRC(2021)·14 citations
02
[Submitted on 19 Mar 2021]
From Kadanoff--Baym to Boltzmann equations for massive spin-1/2 fermions
Xin-Li Sheng🇨🇳 · Nora Weickgenannt🇩🇪 · Enrico Speranza🇺🇸 · Dirk H. Rischke🇩🇪 · Qun Wang🇨🇳
We derive Boltzmann equations for massive spin-1/2 fermions with local and nonlocal collision terms from the Kadanoff--Baym equation in the Schwinger--Keldysh formalism, properly accounting for the spin degrees of freedom. The Boltzmann equations are expressed in terms of matrix-valued spin distribution functions, which are the building blocks for the quasi-classical parts of the Wigner functions. Nonlocal collision terms appear at next-to-leading order in $ℏ$ and are sources for the polarization part of the matrix-valued spin distribution functions. The Boltzmann equations for the matrix-valued spin distribution functions pave the way for simulating spin-transport processes involving spin-vorticity couplings from first principles.
Comments:
RevTex 4, 24 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.10636 [pdf]
PRD(2021)·117 citations
03
[Submitted on 19 Mar 2021]
New effective interactions for hypernuclei in density dependent relativistic mean field model
Yu-Ting Rong🇨🇳 · Zhong-Hao Tu🇨🇳 · Shan-Gui Zhou🇨🇳
New effective $Λ N$ interactions are proposed for the density dependent relativistic mean field model. The multidimensionally constrained relativistic mean field model is used to calculate ground state properties of eleven known $Λ$ hypernuclei with $A \geq 12$ and the corresponding core nuclei. Based on effective $N N$ interactions DD-ME2 and PKDD, the ratios $R_{σ}$ and $R_{ω}$ of scalar and vector coupling constants between $Λ N$ and $N N$ interactions are determined by fitting calculated $Λ$ separation energies to experimental values. We propose six new effective interactions for $Λ$ hypernuclei: DD-ME2-Y1, DD-ME2-Y2, DD-ME2-Y3, PKDD-Y1, PKDD-Y2 and PKDD-Y3 with three ways of grouping and including these eleven hypernuclei in the fitting. It is found that the two ratios $R_{σ}$ and $R_{ω}$ are correlated well and there holds a good linear relation between them. The statistical errors of the ratio parameters in these effective interactions are analyzed. These new effective interactions are used to study the equation of state of hypernuclear matter and neutron star properties with hyperons.
Comments:
11 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.10706 [pdf]
PRC(2021)·36 citations
04
[Submitted on 18 Mar 2021]
Maximum latent heat of neutron star matter independently of General Relativity
Eva Lope-Oter🇪🇸 · Felipe J. Llanes-Estrada (Univ. Complutense de Madrid)🇪🇸
We establish bounds on the maximum possible specific latent heat of cold neutron-star matter derived from hadron physics alone. Existing chiral perturbation theory computations for the equation of state, together with perturbative Quantum Chromodynamics, relevant at highest densities (even if they would turn out not to be physically realizable) bind the maximum latent heat which is possible in actual neutron stars. Because these are already near gravitational collapse in General Relativity, no denser form of cold matter can exist: thus, the bounds are a generic physical limit. Even in scenarios that modify the theory of gravity, the existence of a family of latent-heat maxima is relevant to diagnose progress in the knowledge of the equation of state of neutron matter, by quantifying the maximum possible (presumed) phase transition that its error bands would allow. Thus, latent heat is a natural benchmark for the equation of state in cold QCD.
Comments:
9 plots, six pages in double column Phys. Rev. C format; thoroughly revised version following refereeing. Updated to include (n,mu) integral constraints from Komoltsev and Kurkela's 2111.05350
Subjects:
Nuclear Theory (nucl-th); General Relativity and Quantum Cosmology (gr-qc)
arXiv:
2103.10799 [pdf]
PRC(2022)·15 citations
05
[Submitted on 19 Mar 2021]
Using local nuclear scaling of initial condition parameters to improve the system size dependence of transport model descriptions of nuclear collisions
Chao Zhang🇨🇳 · Liang Zheng🇨🇳 · Shusu Shi🇨🇳 · Zi-Wei Lin🇺🇸
We extensively study the system size dependence of nuclear collisions with a multi-phase transport model. Previously certain key parameters for the initial condition needed significantly different values for $pp$ and central $AA$ collisions for the model to reasonably describe the yields and transverse momentum spectra of the bulk matter in those collision systems. Here we scale two key parameters, the Lund string fragmentation parameter $b_{L}$ and the minijet transverse momentum cutoff $p_{0}$ , with local nuclear thickness functions from the two colliding nuclei. This allows the model to use the parameter values for $pp$ collisions with the local nuclear scaling to describe the system size and centrality dependences of nuclear collisions self consistently. In addition to providing good descriptions of $pp$ collisions from 23.6 GeV to 13 TeV and reasonable descriptions of the centrality dependence of charged particle yields for Au+Au collisions from $7.7 A$ GeV to $200 A$ GeV and Pb+Pb collisions at LHC energies, the improved model can now well describe the centrality dependence of the mean transverse momentum of charged particles below $p_{T} ≲ 2$ GeV. It works similarly well for smaller systems including $p$ Pb, Cu+Cu and Xe+Xe collisions.
Comments:
10 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2103.10815 [pdf]
PRC(2021)·23 citations
06
[Submitted on 19 Mar 2021]
Contribution of $S U (3)$ quadratic Casimir squared to rotational bands in the interacting boson model
Victor Miguel Banda Guzman · Ruben Flores-Mendieta · Johann Hernandez
Rotational bands are commonly used in the analysis of the spectra of atomic nuclei. The early version of the interacting boson model of Arima and Iachello has been foundational to the description of rotations in nuclei. The model is based on a unitary spectrum generating algebra $U (6)$ and an orthogonal (angular momentum) symmetry algebra $S O (3)$ . A solvable limit of the model contains $S U (3)$ in its dynamical symmetry chain. The corresponding Hamiltonian is written as a linear combination of linear and quadratic Casimir invariants of all the algebras in the chain. Prompted by these facts, a Hamiltonian containing the $S U (3)$ quadratic Casimir squared is proposed to evaluate its effects on rotational bands. The additional term yields three undetermined parameters into the theory, which need be obtained from experiment. The lack of data does not allow one to perform a detailed numerical analysis, but a rather restricted one in terms of a one-parameter fit. Nevertheless, these additional terms provide a good description of rotational bands of two nuclei of interest, $^{156} Ga$ and $^{234} U$ .
Comments:
13 pages, 2 figures, 1 table
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.10822 [pdf]
0 citations
07
[Submitted on 19 Mar 2021]
Re-investigation of heat capacity and paring phase transition in hot $^{93 - 98}$ Mo nuclei
Le Thi Quynh Huong · Tran Dong Xuan · Nguyen Ngoc Anh · Nguyen Quang Hung
The empirical heat capacities of $^{93 - 98}$ Mo nuclei are re-investigated by using the latest updated and recommended nuclear level density (NLD) data below the neutron binding energy $B_{n}$ combined with the back-shifted Fermi-gas (BSFG) model for the energy region above $B_{n}$ . For the latter, the BSFG formula with energy-dependent level density parameter is used and the new parameterization has been carried out in order to obtain the best fit to the new NLD data in the whole data range. The results obtained show that the S-shaped heat capacity, a fingerprint of the pairing phase transition, is more pronounced in even $^{94, 96, 98}$ Mo nuclei than that in odd $^{93, 95, 97}$ Mo isotopes. This result is different with those obtained in two previous studies by R. Chankova et al., [Phys. Rev. C {\bf 73}, 034311 (2006)] and K. Kaneko et al., [Phys. Rev. C {\bf 74}, 024325 (2006)], in which the old NLD data and the BSFG model with energy-independent level density parameter were used. Moreover, the present work suggests that the very strong S-shape observed in the heat capacities of both even and odd Molybdenum isotopes by K. Kaneko et al., [Phys. Rev. C {\bf 74}, 024325 (2006)] should be re-investigated. The present work also suggests that obtain the correct heat capacity and associated pairing phase transition in excited nuclei, one should use the correct NLD data and the best fitted BSFG NLD in the entire region where the experimental data are available.
Comments:
6 pages, 3 figures. Accepted in Eur. Phys. J. A
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2103.10841 [pdf]
0 citations
08
[Submitted on 19 Mar 2021]
Rotating deformed halo nuclei and shape decoupling effects
Xiang-Xiang Sun🇨🇳 · Shan-Gui Zhou🇨🇳
We explore the rotational feature of deformed halos by performing the angular momentum projection (AMP) on the ground state wave functions obtained from the deformed relativistic Hartree-Bogoliubov theory (DRHBc) in continuum. The DRHBc+AMP approach self-consistently describes the coupling between single particle bound states and the continuum not only in the ground state but also in rotational states. The rotational modes of deformed halos in $^{42}$ Mg and $^{44}$ Mg are investigated by studying properties of rotational states such as excitation energy, configuration, and density distribution. Our study demonstrates that the deformed halo structure persists from the ground state in the intrinsic frame to collective states. Especially, the typical behavior of shape decoupling effects in rotating deformed halo nuclei is revealed.
Comments:
7 pages, 5 figure, and 1 table
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2103.10886 [pdf]
Sci.Bull.(2021)·64 citations
09
[Submitted on 19 Mar 2021]
Spin-thermal shear coupling in a relativistic fluid
F. Becattini🇮🇹 · M. Buzzegoli🇮🇹 · A. Palermo (University of Florence and INFN)🇮🇹
We show that spin polarization of a fermion in a relativistic fluid at local thermodynamic equilibrium can be generated by the symmetric derivative of the four-temperature vector, defined as thermal shear. As a consequence, besides vorticity, acceleration and temperature gradient, also the shear tensor contributes to the polarization of particles in a fluid. This contribution to the spin polarization vector, which is entirely non-dissipative, adds to the well known term proportional to thermal vorticity and may thus have important consequences for the solution of the local polarization puzzles observed in relativistic heavy ion collisions.
Comments:
10 pages, 1 figure; version accepted for publication in Physics Letters B
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th); Plasma Physics (physics.plasm-ph)
arXiv:
2103.10917 [pdf]
PLB(2021)·195 citations

Affiliations

first authorsco-authorsvia INSPIRE