Nuclear Theory·nucl-th

Wednesday·September 17, 2025

9 papers—5 primary·4 cross-listed

01
[Submitted on 15 Sept 2025]
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.
Comments:
13 pages, 12 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2509.12404 [pdf]
1 citation
02
[Submitted on 16 Sept 2025]
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.
Comments:
Contribution to 14th Spring School of Nuclear Physics, Ischia, Italy, May 2025. To appear in EPJA Web of Conferences
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2509.12549 [pdf]
EPJ Web Conf.(2025)·0 citations
03
[Submitted on 16 Sept 2025]
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.
Comments:
22 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2509.12565 [pdf]
IJMPE(2025)·2 citations
04
[Submitted on 16 Sept 2025]
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.
Comments:
Published in Astrophysical Journal 997 (2026) 26
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2509.12881 [pdf]
ApJ(2026)·7 citations
05
[Submitted on 16 Sept 2025]
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.
Comments:
122 pages. Master's thesis. Any comments are welcome
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)
arXiv:
2509.13037 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Thermal effects on stellar neutron capture reactions: a quantum dynamical approach

A weak entanglement approximation for nuclear structure: review and recent developments

Investigation of ground state properties and shape evolution in Hf isotopes using the CDFT approach

Hyperons in Neutron Stars across the observed mass range: Insights from realistic Λ-N and Λ-Λ interactions within a Microscopic Framework

Reconstruction of the Equations of State (EoSs) of Compact Stars using machine and deep learning regression techniques

Affiliations

Hyperons in Neutron Stars across the observed mass range: Insights from realistic $Λ$ -N and $Λ$ - $Λ$ interactions within a Microscopic Framework