Nuclear Theory·nucl-th

Thursday·December 5, 2024

8 papers—6 primary·2 cross-listed

01
[Submitted on 3 Dec 2024]
Data-driven analysis of dipole strength functions using artificial neural networks
Weiguang Jiang · Tim Egert · Sonia Bacca · Francesca Bonaiti · Peter von Neumann Cosel
We present a data-driven analysis of dipole strength functions across the nuclear chart, employing an artificial neural network to model and predict nuclear dipole responses. We train the network on a dataset of experimentally measured dipole strength functions for 216 different nuclei. To assess its predictive capability, we test the trained model on an additional set of 10 new nuclei, where experimental data exist. Our results demonstrate that the artificial neural network not only accurately reproduces known data but also identifies potential inconsistencies in certain experimental datasets, indicating which results may warrant further review or possible rejection. Additionally, for nuclei where experimental data are sparse or unavailable, the network confirms theoretical calculations, reinforcing its utility as a predictive tool in nuclear physics. Finally, utilizing the predicted electric dipole polarizability, we extract the value of the symmetry energy at saturation density and find it consistent with results from the literature.
Comments:
7 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2412.02876 [pdf]
PRC(2025)·4 citations
02
[Submitted on 4 Dec 2024]
Effects of Landau quantization on neutrino emission and absorption
Mia Kumamoto🇺🇸 · Catherine Welch🇺🇸
Some neutron stars known as magnetars possess very strong magnetic fields, with surface fields as large as $1 0^{15} G$ and internal fields that are possibly stronger. Recent observations of the radio pulsar GLEAM-X J1627 suggest it may have a surface field as strong as $1 0^{16} G$ . In the presence of a strong magnetic field, the energy levels of electrons and protons are quantized and the Direct Urca process allows neutron stars to cool rapidly, even at low density. For the case of magnetic fields $B \geq 1 0^{16} G$ , we find features in the emissivity due to energy quantization that are not captured by the frequently employed quasiclassical approximation where energy levels are treated as nearly continuous. Resonances can result in amplification of the neutrino emissivity at specific densities compared to a calculation that neglects quantization, particularly at low temperature. These effects are not important for the thermal evolution of an entire neutron star, but may be relevant for phenomena that depend on behavior at specific densities. We present a fully relativistic calculation of the Direct Urca rate in a strong magnetic field using the standard V-A weak Lagrangian incorporating mean field nuclear effects and discuss approaches to the numerical challenge the modified wavefunctions present and a new semi-analytic approximation. These tools are also applicable to calculating neutrino opacities in strong magnetic fields in the ejecta of binary neutron star mergers. We calculate the opacities for neutrinos capturing on free nucleons at sub-saturation densities and temperatures exceeding an MeV. We find an enhancement to capture processes of the lowest energy neutrinos by an order of magnitude or more due to suppression of electron Pauli blocking in the case of capture on neutrons, and from the effect of the nucleon magnetic moments in the case of capture on protons.
Comments:
14 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2412.02925 [pdf]
PRD(2025)·8 citations
03
[Submitted on 4 Dec 2024]
Generalized susceptibilities of net-baryon number based on the 3-dimensional Ising universality class
Xue Pan🇨🇳
Assuming the equilibrium of the QCD system, we have investigated the critical behavior of sixth-, eighth- and tenth-order susceptibilities of net-baryon number, through mapping the results in the three-dimensional Ising model to that of QCD. Both the leading critical contribution as well as sub-leading critical contribution from the Ising model are discussed. When considering only the leading critical contribution, the density plots for susceptibilities of the same order demonstrate a consistent general pattern independent on values of mapping parameters. As the critical point is approached from the crossover side, a negative dip followed by a positive peak is observed in the $μ_{B}$ dependence of the three different orders of susceptibilities. When sub-leading critical contribution is taken into account, modifications become apparent in the density plots of the susceptibilities. The emergence of negative dips in the $μ_{B}$ dependence of the susceptibilities is not an absolute phenomenon, while the positive peak structure is a more robust feature of the critical point.
Comments:
9 pages, 5 figures, to be published in Chinese Physics C
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
arXiv:
2412.03014 [pdf]
CPC(2025)·1 citation
04
[Submitted on 4 Dec 2024]
Impact of nuclear masses on r-process nucleosynthesis: bulk properties versus shell effects
Samuel A. Giuliani · Gabriel Martínez-Pinedo · Andreas Bauswein · Vimal Vijayan
We investigate the impact of the model estimating the masses of exotic nuclei on r-process nucleosynthesis, assessing the dependence of the abundance distribution on the specific properties of nuclear masses. By decomposing theoretical nuclear mass predictions into a liquid-drop parametrization and local shell effects, we show that r-process abundances are virtually insensitive to large variations of the masses which originate from nuclear bulk properties of the model, such as the symmetry energy. In contrast, the mass component associated with local shell effects is the main driver of r-process abundance variations, despite its relatively minor contribution to the absolute value of neutron separation energies. Our work suggests that experimental and theoretical studies of masses devoted to r-process applications, such as the nucleosynthesis in the ejecta of neutron star mergers, should focus on the physical origin and determination of local changes in mass trends.
Comments:
9 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2412.03243 [pdf]
PRC(2026)·1 citation
05
[Submitted on 4 Dec 2024]
Evolution of shell structure at $N = 32$ and 34: Insights from realistic nuclear forces
Subhrajit Sahoo · Praveen C. Srivastava
We investigated the evolution of shell structure at $N = 32$ and 34 in neutron-rich nuclei beyond the stability line using realistic nuclear forces, employing the state-of-the-art valence-space in-medium similarity renormalization group method. The shell gaps are discussed from the excitation energies of the first $2^{+}$ states and the evolution of effective single-particle energies. We addressed different components of the nuclear interaction--central, spin-orbit, and tensor--and their roles in the development of shell gaps far from stability. The calculated results align well with the available experimental data and suggest a strengthening of the $N = 34$ subshell gap and a weakening of the $N = 32$ subshell gap below Ca. Additionally, the low-energy structures of the exotic $N = 32$ isotones below Ca revealed that their ground states exhibit large deformation and coexist with a weakly deformed band at low excitation energy. The present work demonstrates essential components of the nuclear force in shaping magic numbers far from stability and provides deeper insights into the structure of exotic nuclei from the underlying nuclear forces.
Comments:
7 pages, 6 figures, 1 table
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2412.03265 [pdf]
PRC(2025)·6 citations
06
[Submitted on 4 Dec 2024]
Impact of hyperons on structural properties of neutron stars and hybrid stars within the regularized four-dimensional Einstein-Gauss-Bonnet gravity
Ishfaq Ahmad Rather🇩🇪 · Grigoris Panotopoulos🇨🇱
We investigate the impact of hyperons and phase transition to quark matter on the structural properties of neutron stars within the regularized four-dimensional Einstein-Gauss-Bonnet gravity (4DEGB). We employ the density-dependent relativistic mean-field model (DDME2) for the hadronic phase and the density-dependent quark mass (DDQM) model for the quark phase to construct hadronic and hybrid equations-of-state (EoSs) that are consistent with the astrophysical constraints. The presence of hyperons softens the EoS and with a phase transition, the EoS further softens, and the speed of sound squared drops to around 0.2 for the maximum mass configuration, which lies in the pure quark phase. Adjusting the Gauss-Bonnet coupling constant, $α$ , within its allowed range results in a decrease in the mass-radius relationship for negative $α$ , and an increase for positive $α$ . In addition, functions are fitted to the maximum mass and its associated radius as a function of the constant $α$ to observe its impact on these properties. We find that positive values of $α$ support massive stars consistent with the 2\, $M_{⊙}$ constraint and NICER measurements, while negative values, although compatible with low-mass radius observations, fail to reach the observed maximum mass, particularly for EoSs involving phase transitions. Therefore, astrophysical observations may be used to effectively constrain the allowed range of $α$ .
Comments:
28 pages, 7 figures, 4 tables
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
arXiv:
2412.03348 [pdf]
Int.J.Geom.Meth.Mod.Phys.(2026)·1 citation
07
[Submitted on 4 Dec 2024] (cross-list from gr-qc)
General Relativistic Hartree-Fock Calculations for Neutron Star
Naoki Onishi
We investigate the global structures of neutron stars within the framework of general relativity, treating the entire star as a quantum-degenerate system. Rather than relying on the Tolman-Oppenheimer-Volkoff (TOV) equation, we solve the Einstein-Cartan (EC) field equations self-consistently, incorporating the energy-momentum tensor contributions from neutrons. Neutron wave functions are obtained by solving the Dirac equation in a curved spacetime with both torsion and curvature effects. Given that neutron stars contain about 10^57 particles, we adopt a scaled h-bar approach to efficiently describe the quantum state of highly degenerate system.
Comments:
15 pages
Subjects:
General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2412.02990 [pdf]
0 citations
08
[Submitted on 4 Dec 2024] (cross-list from quant-ph)
A deep neural network approach to solve the Dirac equation
Chuanxin Wang · Tomoya Naito · Jian Li · Haozhao Liang
We extend the method from [Naito, Naito, and Hashimoto, Phys. Rev. Research 5, 033189 (2023)] to solve the Dirac equation not only for the ground state but also for low-lying excited states using a deep neural network and the unsupervised machine learning technique. The variational method fails because of the Dirac sea, which is avoided by introducing the inverse Hamiltonian method. For low-lying excited states, two methods are proposed, which have different performances and advantages. The validity of this method is verified by the calculations with the Coulomb and Woods-Saxon potentials.
Comments:
16 pages, 16 figures, 3 tables
Subjects:
Quantum Physics (quant-ph); cond-mat.other (cond-mat.other); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
arXiv:
2412.03090 [pdf]
EPJA(2025)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE