Nuclear Theory·nucl-th

Friday·August 23, 2024

6 papers—2 primary·4 cross-listed

01
[Submitted on 22 Aug 2024]
Exploring isospin-nonconserving effects in the upper $f p$ shell with new mass measurements
H.F. Li · X. Xu · Y. Sun · K. Kaneko · X. Zhou · M. Zhang · W.J. Huang · X.H. Zhou · Yu.A. Litvinov · M. Wang · Y.H. Zhang
Nuclear mass measurements have recently been extended conspicuously to proton-rich region in the upper $f p$ shell. The new data are utilized to study isospin symmetry breaking phenomena}using Coulomb displacement energy (CDE) and triplet displacement energy (TDE) as probes. The new mass data, either measured for the first time or with greatly improved accuracy, removed several previously found ``anomalies" in the systematical behavior in the $f p$ shell. Remarkably, more regular odd-even staggering patterns can be established in both CDE and TDE, calling for a uniform explanation in terms of isospin-nonconserving (INC) forces across the $s d$ , $f_{7/2}$ , and upper $f p$ shells. By extending the large-scale shell-model calculation [Phys. Rev. Lett. \textbf{110}, 172505 (2013)] to the upper $f p$ -shell region, we found that, in order to describe the new data, the same INC force is required as previously used for the $f_{7/2}$ shell. Especially, we propose the $T = 1$ TDE for those triplet nuclei, that have $pp$ , $nn$ , and $p n$ pairs on top of a common even-even $N = Z$ core, to be a good indicator for the isotensor component of isospin violating interactions, which is estimated here to be 150 keV.
Comments:
7 pages, 2 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2408.12281 [pdf]
PRC(2024)·4 citations
02
[Submitted on 22 Aug 2024]
Non-extensive (3+1)-dimensional hydrodynamics for relativistic heavy-ion collisions
Jia-Hao Shi🇨🇳 · Zhi-Ying Qin🇨🇳 · Jin-Peng Zhang🇨🇳 · Jian Cao🇨🇳 · Ze-Fang Jiang🇨🇳 · Wen-Chao Zhang🇨🇳 · Hua Zheng🇨🇳
A non-extensive (3+1)-dimensional hydrodynamic model for multi-particle production processes, NEX-CLVisc, is developed in the framework of CLVisc where the viscous corrections are turned off. It assumes that the non-extensive effects consistently exist in the initial conditions set by the optical Glauber model, the equation of state and the hadron kinetic freeze-out procedure. The model is then applied to simulate the pseudo-rapidity ( $η$ ) distribution, the transverse momentum ( $p_{T}$ ) spectra and the $p_{T}$ -differential elliptic flow ( $v_{2}$ ) of charged particles in Pb-Pb collisions at $s_{NN} =$ 2.76 TeV and 5.02 TeV, respectively. It is found that the model can reasonably well reproduce the experimental data of the $η$ distribution and the charged-particle spectra in a $p_{T}$ range up to 6-8 GeV/c. When compared with the ideal hydrodynamic model, the $p_{T}$ -differential $v_{2}$ of charged particles is suppressed in the NEX-CLVisc model, which is similar to that observed in the hydrodynamic model with a shear viscous correction. Moreover, due to the lack of the viscous corrections and the event-by-event fluctuation, the model can only describe the $p_{T}$ -differential $v_{2}$ up to 3-4 GeV/c, which is smaller than its applicable range for the particle $p_{T}$ spectra.
Comments:
9 pages, 4 figures, 4 tables. Revised accroding to the referee's comments
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2408.12405 [pdf]
PRD(2025)·11 citations
03
[Submitted on 21 Aug 2024] (cross-list from astro-ph.HE)
Layers of electron captures in the crust of accreting neutron stars
Lami Suleiman🇺🇸 · Julian-Leszek Zdunik🇵🇱 · Pawel Haensel🇵🇱
The accumulation of accreted matter onto the neutron star surface triggers exothermic reactions in the crust. The heat released as a result influences the luminosity exhibited by the X-ray transient. The most common approach to the kinetics of exothermic reactions in the crust of accreting neutron stars is to consider an infinite reaction rate. Here, we investigate accretion-related heat release in the accreted outer crust of a neutron star by including a time-dependent accretion cycle and experimentally based reaction rates in the kinetics of electron captures above the reaction threshold. A simple model was used to compute the zero temperature equation of state of a crust in which two nuclei can coexist. We solved the abundance of parent nuclei as a function of the depth in the star and the time variable using astrophysically motivated features of the accreting system. We calculated the heat release and neutrino loss associated to reactions in the outer crust. We report the existence of layers in the outer crust, which contain both parent and grand-daughter nuclei of electron captures. The reactions can occur deeper in the shell than the reaction threshold, thus releasing more heat per accreted baryon for a given accretion rate. The electron capture layers continue to exist even when the accretion has stopped. The heat sources are time- and pressure-dependent in accreting crusts of neutron stars. The total heat released is a function of astrophysical (active and quiescent time) and microscopic (reaction rate) parameters Therefore, we conclude these parameters should be considered individually and carefully for a range of different sources.
Comments:
14 pages, 5 figures, 4 tables, 2 appendices, accepted for publication in Astronomy & Astrophysics
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2408.11999 [pdf]
Astron.Astrophys.(2024)·2 citations
04
[Submitted on 22 Aug 2024] (cross-list from hep-ph)
Color superconductivity and speed of sound in the two-flavor quark-meson diquark model
Jens O. Andersen🇳🇴 · Mathias P. Nødtvedt🇳🇴
We discuss the properties of the two-flavor quark-meson diquark (QMD) model as a renormalizable low-energy model for QCD in the 2SC phase of QCD. The effective degrees of freedom are the mesons (sigma and pions), quarks, and diquarks. Some of the parameters of the model can be determined by expressing them in terms of the vacuum meson masses and the pion decay constant using the on-shell renormalization scheme. The remaining parameters are considered free, although they in principle can be calculated from QCD. The thermodynamic potential is calculated in a mean-field approximation taking only quark loops into account. In this approximation, we derive a set of renormalization group equations for the running masses and couplings. The solutions to these equations are used to improve the thermodynamic potential $Ω$ and thereby thermodynamic quantities. Four parameter sets are chosen and the phase diagram in the $μ ˉ$ -- $T$ plane is obtained (with $μ ˉ = \frac{1}{3} μ_{B}$ ). We also calculate the speed of sound $c_{s}$ as a function of $μ ˉ$ at vanishing temperature. For large values of $μ ˉ$ , the speed of sound approaches the conformal limit $c_{s} = \frac{1}{3}$ from above, in disagreement with perturbative calculations, but agreement with hard-dense-loop resummed perturbation theory.
Comments:
14 pages, 7 figures, V2: Extended discussion on speed of sound, hence modified title
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2408.12361 [pdf]
PRD(2025)·18 citations
05
[Submitted on 22 Aug 2024] (cross-list from hep-ph)
Interplay between the weak-coupling results and the lattice data in dense QCD
Yuki Fujimoto🇺🇸
We discuss the interplay between two first-principles calculations of QCD at high density: perturbative results in the weak-coupling regime and the recent lattice-QCD result at finite isospin density. By comparing these two results, we verify empirically that the weak-coupling calculations of the bulk thermodynamics and the gap parameter for Cooper pairing between quarks can be applicable down to the quark chemical potential $μ \sim 1$ GeV. Having verified the validity of the weak-coupling results in QCD at finite isospin density, we discuss possible effects on QCD at finite baryon density, which is relevant for the application to realistic environments such as neutron stars, by using the fact that QCD at finite baryon and isospin density have the common weak-coupling expansions. First, we show the size of the color-superconducting gap at finite baryon density is as small as a few MeV at $μ = 1$ GeV, which implies that the color-flavor locked phase may be unstable against unpairing up to $μ \sim 1.4$ GeV even in the weak-coupling regime. We also introduce a prescription to reduce the ambiguity arising from the undetermined renormalization scale in the weak-coupling calculation by matching with the lattice-QCD data. We demonstrate the effect of such reduction on neutron-star phenomenology by performing the Bayesian analysis.
Comments:
9 pages, 4 figures; v2: corrected Eq. (1), results unchanged
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2408.12514 [pdf]
15 citations
06
[Submitted on 22 Aug 2024] (cross-list from hep-ph)
Spectral eigenfunction decomposition of a Fokker-Planck operator for relativistic heavy-ion collisions
A. Rizzi🇩🇪 · G. Wolschin🇩🇪
A spectral solution method is proposed to solve a previuously developed non-equilibrium statistical model describing partial thermalization of produced charged hadrons in relativistic heavy-ion collisions, thus improving the accuracy of the numerical solution. The particle's phase-space trajectories are treated as drift-diffusion stochastic process, leading to a Fokker-Planck equation (FPE) for the single-particle probability distribution function. The drift and diffusion coefficients are derived from the expected asymptotic states via appropriate fluctuation-dissipation relations, and the resulting FPE is then solved numerically using a spectral eigenfunction decomposition. The calculated time-dependent particle distributions are compared to Pb-Pb data from the ATLAS and ALICE collaborations at the Large Hadron Collider.
Comments:
17 pages, 8 figures; submitted to Eur. Phys. J. A
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2408.12532 [pdf]
EPJA(2024)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Exploring isospin-nonconserving effects in the upper fp shell with new mass measurements

Non-extensive (3+1)-dimensional hydrodynamics for relativistic heavy-ion collisions

Layers of electron captures in the crust of accreting neutron stars

Color superconductivity and speed of sound in the two-flavor quark-meson diquark model

Interplay between the weak-coupling results and the lattice data in dense QCD

Spectral eigenfunction decomposition of a Fokker-Planck operator for relativistic heavy-ion collisions

Affiliations

Exploring isospin-nonconserving effects in the upper $f p$ shell with new mass measurements