Nuclear Theory·nucl-th

Thursday·June 13, 2024

10 papers—4 primary·6 cross-listed

01
Shear Viscosity of an $N$ -Component Gas Mixture using the Chapman--Enskog Method under Anisotropic Scatterings
Noah M. MacKay
The analytical Chapman-Enskog formula for calculating the shear viscosity $η$ of a relativistic ideal gas, such as a massless quark-gluon plasma, has consistently demonstrated good agreement with the numerical results obtained using the Green-Kubo relation under both isotropic and anisotropic two-body scatterings. However, past analyses of massless, multicomponent quark-gluon plasma have focused on an effective single-component "gluon gas." The Chapman-Enskog formula for multicomponent mixtures with nonzero yet adjustable masses was previously developed for simpler cases of isotropic scatterings. This study aims to obtain the Chapman-Enskog shear viscosity formula for a massless, multicomponent mixture under general anisotropic scatterings. Since the shear viscosity depends on a linearized collision kernel, an approximation formula for the linearized collision kernel is derived under elastic and anisotropic $l + k \to l + k$ scatterings. This derived approximation agrees very well with the isotropic two-body kernels provided in previous works for both like and different species. Furthermore, for multicomponent mixtures beyond two species types, an alternative expansion method of the $N$ -component Chapman-Enskog viscosity is presented. This is applied to a two-component "binary" mixture and compared with the conventional formula for binary viscosity. The agreement between the two, for interacting and noninteracting binary mixtures, varies from moderate to well.
nucl-thhep-th2 citations
02
Ab initio calculations with a new local chiral N3LO nucleon-nucleon force
P. Y. Wang · J. G. Li · S. Zhang · Q. Yuan · M. R. Xie · W. Zuo
Ab initio calculations have achieved remarkable success in nuclear structure studies. Numerous works highlight the pivotal role of three-body forces in nuclear ab initio calculations. Concurrently, efforts have been made to replicate these calculations using only realistic nucleon-nucleon (NN) interactions. A novel local chiral next-to-next-to-next-to-leading order (N3LO) NN interaction, distinct due to its weaker tensor force, has recently been established. This paper applies this local NN interaction in ab initio frameworks to calculate the low-lying spectra of p-shell light nuclei, particularly 10B, ground-state energies and shell evolution in oxygen isotopes. Results are compared with calculations utilizing nonlocal chiral N3LO NN and chiral NN +3N interactions. The ab initio calculations with the local N N potential accurately describe the spectra of p-shell nuclei, notably the 10B. Additionally, the neutron drip line for oxygen isotopes, with 24O as the drip line nucleus, is accurately reproduced in ab initio calculations with the local NN interaction. Calculations with the local NN interaction also reproduce the subshell closure at N = 14 and 16, albeit with a stronger shell gap compared to experimental data. However, the calculated charge radii based on the local NN interaction are underestimated compared with experimental data, which is similar to results from the nonlocal NN interaction. Consequently, the present ab initio calculations further indicate significant spin-orbit splitting effects with the new local NN potential, suggesting that 3N forces remain an important consideration.
nucl-thPRC(2024)·7 citations
03
Towards a unified description of isotopic fragment properties in spontaneous and fusion-induced fission within a 4D dynamical Langevin model
K. Pomorski🇵🇱 · B. Nerlo-Pomorska🇵🇱 · J. Bartel🇫🇷 · C. Schmitt🇫🇷 · Z. G. Xiao🇨🇳 · Y. J. Chen🇨🇳 · L. L. Liu🇨🇳
Spontaneous fission of 252Cf and fusion-induced fission of 250Cf are investigated within a multi-dimensional Langevin model. The potential-energy surface is calculated in the macroscopic-microscopic LSD+Yukawa-folded approach using the four-dimensional Fourier-over-Spheroid shape parametrization. The dynamical evolution described by the Langevin equation is coupled to neutron evaporation, thereby allowing for the possibility of multi-chance fission. Charge equilibration and excitation-energy sharing between the fragments emerging at scission are evaluated, and their de-excitation is finally computed. The correlation between various observables, particularly the isotopic properties of the fragments, is discussed and compared with the experiment whenever available. The theoretical predictions are generally in good agreement with the data.
nucl-thPRC(2024)·11 citations
04
Unveiling potential neutron halos in intermediate-mass nuclei: an \textit{ab initio} study
H. H. Li · J. G. Li · M. R. Xie · W. Zuo
Halos epitomize the fascinating interplay between weak binding, shell evolution, and deformation effects, especially in nuclei near the drip line. In this Letter, we apply the state-of-the-art \textit{ab initio} valence-space in-medium similarity renormalization group approach to predict potential candidates for one- and two-neutron halo in the intermediate-mass region. Notably, we use spectroscopic factors (SF) and two-nucleon amplitudes (TNA) as criteria for suggesting one- and two-neutron halo candidates, respectively. This approach is not only theoretically sound but also amenable to experimental validation. Our research focuses on Mg, Al, Si, P, and S neutron-drip-line nuclei, offering systematic predictions of neutron halo candidates in terms of separation energies, SF (TNA), and average occupation. The calculation suggests the ground states of $^{40, 42, 44, 46}$ Al, $^{41, 43, 45, 47}$ Si, $^{46, 48}$ P, and $^{47, 49}$ S are promising candidates for one-neutron halos, while $^{40, 42, 44, 46}$ Mg, $^{45, 47}$ Al, $^{46, 48}$ Si, $^{49}$ P, and $^{50}$ S may harbor two-neutron halos. In addition, the relative mean-square neutron radius between halo nuclei and \textit{inner core} is calculated for suggested potential neutron halos. Finally, the relations of halo formations and shell evolution are discussed.
nucl-thPRC(2024)·11 citations
05
Jet quenching in the glasma phase: medium-induced radiation
João Barata🇺🇸 · Sigtryggur Hauksson🇫🇷 · Xoán Mayo López🇪🇸 · Andrey V. Sadofyev🇵🇹
Inspired by the recent considerations of parton momentum broadening in the glasma phase, we study the medium-induced soft gluon radiation of jet partons at early times in heavy-ion collisions. The glasma state is assumed to be comprised of independent color domains with homogenous longitudinal fields that vary event by event, and we further complete this model with an event-averaging procedure accounting for the finite correlation length. Using this description, we evaluate the rate of medium-induced radiation from an energetic parton at midrapidity in the glasma phase. We mainly focus on SU(2) color fields for simplicity, also referring to the U(1) case and comparing with the BDMPS-Z rate to gain further insight. Our results show that there is an intricate interplay of the synchrotron-like radiation in a single color domain with the destructive interference between different color domains, after the medium averaging is performed. Thus, we find that the emission rate is sensitive to the matter structure, decreasing for a glasma state populated by smaller color domains, i.e. for a glasma with a larger characteristic saturation scale. Our approach can be applied to more realistic backgrounds, and sets the stage for the modelling of jet evolution in the early stages of heavy-ion collisions.
↳ hep-phnucl-thPRD(2024)·36 citations
06
Semi-Analytical Fokker Planck Models for Nuclear Star Clusters
Karamveer Kaur · Barak Rom · Re'em Sari
We study the dynamics of nuclear star clusters, the dense stellar environments surrounding massive black holes in the centers of galaxies. We consider angular momentum diffusion due to two-body scatterings among stellar objects and energy advection due to gravitational wave emission upon interaction with the central massive black hole. Such dynamics is described by a two-dimensional Fokker-Planck equation in energy-angular momentum space. Focusing on the transition between the diffusion-dominated region and the advection-dominated one, we utilize self-similarity to obtain a full solution for the Fokker-Planck equation. This solution provides the density and flux of the stellar objects in nuclear star clusters. This improves the rate estimates for extreme mass-ratio inspirals, and has interesting implications for a new class of galactic center transients called quasi-periodic eruptions.
↳ astro-ph.HEnucl-thApJ(2025)·13 citations
07
Lighting up the Photon Wigner Distribution via Dilepton Productions
Yu Shi🇨🇳 · Lin Chen🇨🇳 · Shu-Yi Wei🇨🇳 · Bo-Wen Xiao🇨🇳
We present a systematic investigation of lepton pair production through photon-photon fusion processes in heavy-ion collisions. It is demonstrated that the dilepton production at a given impact parameter ( $b_{⊥}$ ) with a fixed transverse momentum imbalance ( $q_{⊥}$ ) can be factorized into a unified formula in terms of the Wigner photon distribution of heavy nuclei. We show that this framework provides a comprehensive description of all the relevant data from RHIC to the LHC, with a strong evidence that the quasi-real photon can be radiated not only from the nucleus as a whole, standing for the coherent contribution, but also from the sub-structures inside the nucleus, representing the incoherent contribution. Further predictions are made for the anisotropies in the correlations between $q_{⊥}$ , $b_{⊥}$ , and the dilepton transverse momentum ( $P_{⊥}$ ). This will help us to constrain the photon Wigner distribution which plays a crucial role to study the gluonic matter of nucleus at small- $x$ through the diffractive photoproduction processes in heavy ion collision.
↳ hep-phhep-exnucl-exnucl-thPLB(2025)·13 citations
08
Off-shell pion properties: electromagnetic form factors and light-front wave functions
Jurandi Leão (Laboratório de Física Teórica e Computacional-LFTC, Universidade Cruzeiro do Sul / Universidade Cidade de São Paulo Paulo, São Paulo, SP, Brazil, and Instituto Federal de São Paulo, Caraguatatuba, SP, Brazil)🇧🇷 · J. Pacheco B. C. de Melo (Laboratório de Física Teórica e Computacional-LFTC, Universidade Cruzeiro do Sul / Universidade Cidade de São Paulo Paulo, São Paulo, SP, Brazil)🇧🇷 · T. Frederico (Instituto Tecnológico de Aeronáutica, São José dos Campos, SP, Brazil)🇧🇷 · Ho-Meoyng Choi (Department of Physics, Teachers College, Kyungpook National University, Daegu, Korea)🇰🇷 · Chueng-Ryong Ji (Department of Physics, North Carolina State University, Raleigh, NC, USA)🇺🇸
The off-shell pion electromagnetic form factors are explored with corresponding off-shell light-front wave functions modeled by constituent quark and anti-quark. We apply the Mandelstam approach for the microscopic computation of the form factors relating the model parameters with the pion decay constant and charge radius. Analyzing the existing data on the cross-sections for the Sullivan process, H(e,e',pi)n, we extract the off-shell pion form factor using the relation derived from the generalized Ward-Takahashi identity for the pion electromagnetic current. They are compared with our previous results from exactly solvable manifestly covariant model of a (3+1)-dimensional fermion field theory. We find that the adopted constituent quark model reproduces the extracted off-shell form factor $F_{1} (Q^{2}, t)$ from the experimental data within a few percent difference and matches well with our previous theoretical simulation which exhibits a variation of about 10\% for the extracted off-shell pion form factor $g (Q^{2}, t)$ . We also identify the pion valence parton distribution function (PDF) and transverse momentum distribution (TMD) in terms of the light-front wave function and discuss their off-shell properties.
↳ hep-phnucl-thPRD(2024)·9 citations
09
Weak interaction axial form factors of the octet baryons in nuclear medium
G. Ramalho🇰🇷 · K. Tsushima🇧🇷 · Myung-Ki Cheoun🇰🇷
We study the axial-vector and the induced pseudoscalar form factors associated with the weak transitions between the octet baryon members in nuclear medium, using a covariant constituent quark model. We extend previous calculations of the axial transition form factors from the vacuum (free space) to the nuclear medium (symmetric nuclear matter). The extension of the model to the nuclear medium takes into account the modifications of the properties of hadrons in the medium (masses and coupling constants), as determined by the quark-meson coupling model. The axial-vector ( $G_{A}$ ) and the induced pseudoscalar ( $G_{P}$ ) form factors are evaluated for different values of the nuclear density $ρ$ in terms of the square transfer momentum $q^{2} = - Q^{2}$ . We conclude that, in general, the $G_{A}$ and $G_{P}$ form factors are reduced in the nuclear medium. The reduction is stronger for light baryons and high densities. The medium modifications are milder for the heavier octet baryons, particularly at large $Q^{2}$ . The calculations presented here can be used to estimate the cross sections of neutrino and antineutrino scattering with nucleus, and neutrino and antineutrino scattering with hyperons bound to a nucleus, as well as those in the cores of compact stars.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2025)·9 citations
10
Constraining the axial-vector X17 interpretation with $^{12}$ C data
Cornelis J.G. Mommers🇩🇪 · Marc Vanderhaeghen🇩🇪
Recent findings of an unexpected, narrow resonance in the $e^{+} e^{-}$ decay spectra of excited states of $^{8}$ Be, $^{4}$ He and $^{12}$ C by the ATOMKI collaboration have received considerable experimental and theoretical attention, whereby a new, 17-MeV vector-like or axial-vector-like boson termed X17 was conjectured as an explanation of the anomaly. Further analysis of all existing constraints disfavors a vector X17 scenario. For a similar analysis of the axial-vector scenario, a calculation of the reduced matrix element of a spin-dipole operator between the excited nuclear state $^{12}$ C(17.23) and the carbon ground state is required. In the present work, we compute the aforementioned reduced matrix element under the assumption that the state $^{12}$ C(17.23) is well represented by the $2 s_{1/2} 1 p_{3/2}^{- 1}$ particle-hole shell-model excitation of the ground state, as supported by experimental data. Within such a framework, our results indicate that, like the vector scenario, the axial-vector interpretation of X17 shows strong tensions with the other existing constraints on the nucleon coupling of a conjectured X17.
↳ hep-phnucl-thPLB(2024)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE