Nuclear Theory·nucl-th

Wednesday·September 17, 2025

9 papers—5 primary·4 cross-listed

01
Thermal effects on stellar neutron capture reactions: a quantum dynamical approach
N. Lightfoot · A. Diaz-Torres · P. Stevenson
The neutron capture process plays a vital role in creating the heavy elements in the universe. Astrophysical environments involved in these processes are characterized by two distinct reaction mechanisms: the slow and rapid neutron capture processes. In this work, the slow neutron capture process is described with the time-dependent coupled channels wave-packet (TDCCWP) method that uses both a many-body nuclear potential and an initial temperature-dependent state to account for the thermal environment. To evaluate the role of a mixed and entangled initial state in the temperature-dependent neutron capture cross section, TDCCWP calculations are compared with those from the coupled-channels density matrix (CCDM) method based on the Lindblad master equation. The importance of including temperature in the initial wave-function of the TDCCWP approach is compared to a thermalisation of the reaction rate using a Hauser-Feshbach style approach. TDCCWP calculations indicate a decrease of the n+ $^{188}$ Os capture cross section with increasing temperature, along with a decrease in reaction rates for the highest thermal energies studied, which are contrary to Hauser-Feshbach calculations and important in the rapid neutron capture process. The physical reason for this discrepancy is the key role of the dynamical nuclear coupling between the thermally populated states of the target nucleus, which is neglected in the Hauser-Feshbach approach, but creates a dominant neutron capture pathway with increased neutron speed and thus reduces the neutron capture cross section.
nucl-th1 citation
02
A weak entanglement approximation for nuclear structure: review and recent developments
Calvin W. Johnson
The nuclear shell model is a useful and widely used tool for nuclear structure, but it can be hampered by the exponential growth of the basis. Drawing inspiration from quantum information theory, one can show that the proton and neutron components are typically weakly entangled. This has led to the Proton And Neutron Approximate Shell-model (PANASh). I review the underlying ideas and present recent developments. In particular I show how PANASh can accelerate beyond-mean-field methods such as the generator coordinate method.
nucl-thEPJ Web Conf.(2025)·0 citations
03
Investigation of ground state properties and shape evolution in Hf isotopes using the CDFT approach
Usuf Rahaman
The ground-state properties and shape evolution of even-even hafnium isotopes ranging from $N = 80$ to the neutron dripline are thoroughly examined using Covariant Density Functional Theory (CDFT) with density-dependent effective interactions, specifically the parameter sets DD-ME1, DD-ME2, DD-PC1, and DD-PCX. Key nuclear properties, including binding energies, two-neutron separation energies ( $S_{2 n}$ ), two-neutron shell gaps ( $δ S_{2 n}$ ), neutron pairing energies ( $E_{p ai r, n}$ ), quadrupole deformation parameters ( $β_{2}$ ), root-mean-square (RMS) charge and matter radii, and neutron skin thickness ( $Δ r_{n p}$ ), are systematically computed and compared with available experimental results and predictions from various theoretical models. These include the Hartree-Fock-Bogoliubov (HFB) framework employing the Skyrme SLy4 interaction, the Finite Range Droplet Model (FRDM), the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) using the PC-PK1 functional, and the relativistic mean-field (RMF) approach with NL3 parameterization. Shell closures at $N = 82$ and $N = 126$ , subshell effects at $N = 108$ and $N = 152$ , and shape transitions with coexistence in $^{192}$ Hf and $^{222 - 236}$ Hf are observed. Neutron skin thickness increases with neutron excess, and potential energy surfaces show consistent trends, validating CDFT's reliability for nuclear structure predictions.
nucl-thnucl-exIJMPE(2025)·2 citations
04
Hyperons in Neutron Stars across the observed mass range: Insights from realistic $Λ$ -N and $Λ$ - $Λ$ interactions within a Microscopic Framework
Ali Mohammad Ali Looee🇮🇷 · Mahboubeh Shahrbaf🇵🇱 · Hamid Reza Moshfegh🇮🇷
We investigate the equation of state (EOS) and macroscopic properties of neutron stars (NSs) and hyperonic stars within the framework of the lowest order constrained variational (LOCV) method, extended to include interacting $Λ$ hyperons. The nucleon-nucleon interaction is modeled using the AV18 potential supplemented by Urbana three-body forces, while $Λ N$ and $ΛΛ$ interactions are described by realistic spin- and parity-dependent potentials fitted to hypernuclear data. Cold, charge-neutral, and $β$ -equilibrated matter composed of neutrons, protons, electrons, muons, and $Λ$ hyperons is considered. We compute particle fractions, chemical potentials, the EOS, speed of sound, tidal deformability, and stellar structure by solving the Tolman-Oppenheimer-Volkoff equations, and compare our results with recent NICER and gravitational-wave observations. The inclusion of $Λ$ hyperons leads to EOS softening, reducing the maximum NS mass from $2.34 M_{⊙}$ to $2.07 M_{⊙}$ , while keeping it consistent with the $2 M_{⊙}$ mass constraint. At $1.4 M_{⊙}$ , the model satisfies observational limits on radius and tidal deformability, with the $Λ$ onset occurring below this mass. Comparison with other microscopic and relativistic mean-field models shows that our EOS remains consistent with the allowed pressure-energy density range, while also permitting even canonical-mass NSs of about $1.4 M_{⊙}$ to accommodate hyperons. These results suggest that hyperons can appear in NSs across the observed mass range without violating current astrophysical constraints, and that the extended LOCV method provides a consistent, microscopic approach to modeling dense hypernuclear matter.
nucl-thastro-ph.HEApJ(2026)·7 citations
05
Reconstruction of the Equations of State (EoSs) of Compact Stars using machine and deep learning regression techniques
Ioannis Stergakis
This dissertation focuses on the reconstruction of Equations of State (EoSs) describing the interior of compact stars, using modern machine learning and deep learning methods. The pipeline is based on data from mass-radius (M-R) curves, obtained by numerically solving the Tolman-Oppenheimer-Volkoff equations for a wide range of admissible EoSs. The manuscript is divided into a Theoretical Part (Chs. 1-4) and a Computational Part (Chs. 5-7). The theoretical chapters analyze the properties of neutron and quark stars, the physical constraints of viable EoS models, and introduce regression algorithms (Decision Tree, Random Forest, Gradient Boosting, XGBoost) and neural networks with normalization and dropout techniques. The computational part presents the generation of artificial EoSs for hadronic and quark stars (MIT bag, CFL), the numerical solution of the TOV equations, data preparation, and hyperparameter tuning. Results include training and evaluation of models using MSE/MSLE metrics, learning curves for neural networks, and reconstruction of 21 hadronic and 20 quark star EoSs. Source code and tools for reproducibility and future research are provided. The work aims to establish a reusable and scalable framework, strengthening the connection between theoretical astrophysics and computational science.
nucl-thastro-ph.HEastro-ph.SRgr-qc0 citations
06
Radial Oscillations of Viscous Neutron Stars: Zero Diffusion Case
Raissa F. P. Mendes🇧🇷 · Amanda Guerrieri🇧🇷 · João V. M. Muniz🇧🇷 · Gabriel S. Rocha🇧🇷 · Gabriel S. Denicol🇧🇷
The spectrum of radial oscillations of neutron stars is systematically studied within two frameworks of viscous relativistic hydrodynamics: the relativistic Navier-Stokes and Israel-Stewart theories. A correspondence is established between the discrete stellar eigenmodes and the continuous dispersion relation of perturbations around a homogeneous fluid, providing a basis for interpreting our numerical results. We analyze the Newtonian limit and assess the impact of relativistic corrections, such as the gravitational redshifting of microscopic relaxation timescales. We show that bulk viscosity can significantly affect the behavior of both hydrodynamic and nonhydrodynamic fundamental modes, and that, depending on the magnitude of the viscous effects, it is the nonhydrodynamic mode that becomes unstable beyond the turning point in a sequence of equilibrium configurations. These results provide a useful step toward systematic studies of neutron star quasinormal modes in the presence of viscosity.
↳ gr-qcnucl-thPRD(2026)·7 citations
07
Coupled-channel analysis for vector charmonia and their nature
Satoshi X. Nakamura (Shandong University)🇨🇳
High-precision $e^{+} e^{-} \to c c ˉ$ data (20 final states) from the BESIII and Belle in $s = 3.75 - 4.7$ GeV are analyzed with a semi three-body unitary coupled-channel model. Vector charmonium poles are extracted from the amplitudes obtained from the fit. We find well-known $ψ$ states listed in the PDG, and also several states near open-charm thresholds. The compositeness of the near-threshold poles suggests that $ψ (4040)$ could mainly consist of a $D^{*} D ˉ^{*}$ -molecule component, rather than a conventionally accepted quark-model $ψ (3 S)$ state. Also, $ψ (4230)$ and $ψ (4360)$ might be substantial mixtures of $D_{1} (2420) D ˉ$ , $D_{1} (2420) D ˉ^{*}$ , $D_{s}^{*} D ˉ_{s}^{*}$ , and $c c ˉ$ components.
↳ hep-phhep-exnucl-thJUSTC 55, 1207 (2025)·0 citations
08
Nuclear Suppression in Diffractive Vector Meson Production within the Color Glass Condensate Framework
Heikki Mäntysaari🇫🇮 · Hendrik Roch🇺🇸 · Farid Salazar🇺🇸 · Björn Schenke🇺🇸 · Chun Shen🇺🇸 · Wenbin Zhao🇺🇸
We extend a recent global Bayesian analysis of diffractive $J / ψ$ production in $γ + p$ and $γ + Pb$ collisions within the color glass condensate (CGC) framework to investigate potential modifications of the nucleon structure inside nuclei. To this end, we perform fits that allow the effective nucleon structure parameters in Pb nuclei to differ from those of free protons. This approach directly addresses the question of whether the proton's spatial gluon distribution at intermediate to large $x$ is modified in the nuclear environment. We compare results obtained with shared and independent nucleon structure parameters and assess the impact on the simultaneous description of $γ + p$ data from HERA and the LHC, as well as $γ + Pb$ data from the LHC. Our findings show that there is no hint of difference in the nucleon structure beyond those already present in the CGC when embedding nucleons inside a nuclear environment.
↳ hep-phnucl-th2 citations
09
Rotating neutron stars within the macroscopic effective-surface approximation
A.G. Magner🇺🇦 · S.P.Maydanyuk🇺🇦 · A. Bonasera🇺🇸 · H. Zheng🇨🇳 · S.N. Fedotkin🇺🇦 · A.I. Levon🇺🇦 · T. Depastas🇺🇸 · U.V. Grygoriev🇺🇦 · A.A. Uleiev🇺🇦
The macroscopic model for a neutron star (NS) as a finite perfect fluid at the equilibrium is extended to rotating systems by incorporating the linear perturbation expansion over a small frequency $ω$ near Schwarzschild outer-inner gravitational metric within the effective-surface (ES) approach. The NS angular momentum $I$ and moment of inertia (MI) for a slow stationary azimuthal rotation around the symmetry axis are calculated by using the Kerr metric approach in spherical coordinates, and compared with Boyer-Lindquist (outer) and Hogan (inner) metric results. The volume and gradient-surface terms of the macroscopic NS energy density $E (ρ)$ (Equation of State) are taken into account at the leading order of the leptodermic parameter $a / R ≪ 1$ , where $a$ is the ES crust thickness and $R$ is the NS effective radius. The analytical macroscopic NS MI expressions, $Θ = d I / d ω = Θ ~ / (1 - T_{tφ})$ , have been obtained in terms of the statistically averaged MI, $Θ ~$ , and its time and azimuthal-angle $t, φ$ correlation, $T_{tφ}$ , as sums of the volume and surface components. The MI $Θ$ is changed significantly as function of the effective radius $R$ because of a strong gravity. We found the additional constraint for the NS radius to smaller accessible ranges which is due mainly to the $t, φ$ correlations and surface contributions. The adiabaticity conditions for applicability of the linear perturbation theory is carried out for several neutron stars with a strong gravity and relatively large rotation periods.
↳ gr-qcastro-ph.HEastro-ph.SRnucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE