Nuclear Theory·nucl-th

Tuesday·December 23, 2025

18 papers—9 primary·9 cross-listed

01
Octupole deformation in quasiparticle states of odd-mass and odd-odd nuclei
N. Kontowicz🇫🇷 · L. Bonneau🇫🇷 · J. Bartel🇫🇷 · H. Molique🇫🇷 · N. Minkov🇧🇬 · M.-H. Koh🇲🇾
As a follow up of [Phys. Scr. 99 055305 (2024)], where we studied axial octupole shapes in two-quasiparticle states of even-even nuclei, we investigate this type of shapes in odd-mass and odd-odd well-deformed nuclei, using the Skyrme-Hartree-Fock-BCS approach with selfconsistent blocking and a constraint on the expectation value $Q_{30}$ of the axial octupole moment operator. To interprete the pattern of the resulting deformation energy curve as a function of $Q_{30}$ , we extend the perturbative mechanism of Ref. [1]. We deduce selection rules which can predict, from the single-particle spectra at $Q_{30} = 0$ , whether in a given multiquasiparticle state the deformation energy curve has a local minimum at a vanishing or a finite value of $Q_{30}$ . The predictions of this perturbative mechanism are compared with actual Skyrme-Hartree-Fock-BCS calculations with a constraint on the expectation value $Q_{30}$ . Overall we obtain a qualitative agreement and we show that quantitative predictions are limited by the role of pairing correlations and strong octupole coupling between quasi-degenerate members of a single-particle parity doublet.
nucl-th0 citations
02
Superfluid fraction in the crystal phase of the inner crust of neutron stars
Giorgio Almirante🇫🇷 · Theodora Kaskitsi🇫🇷 · Michael Urban🇫🇷
In the most extended layer of the inner crust of neutron stars, nuclear matter is believed to form a crystal of clusters immersed in a superfluid neutron gas. Here we analyze this phase of matter within fully self-consistent Hartree-Fock-Bogoliubov calculations using Skyrme-type energy density functionals for the mean field and a separable interaction in the pairing channel. The periodicity of the lattice is taken into account using Bloch boundary conditions, in order to describe the interplay between band structure and superfluidity. A relative flow between the clusters and the surrounding neutron gas is introduced in a time-independent way. As a consequence, the complex order parameter develops a phase, and in the rest frame of the superfluid one finds a counterflow between neutrons inside and outside the clusters. The neutron superfluid fraction is computed from the resulting current. Our results indicate that at densities above 0.03 fm $^{- 3}$ , more than 90% of the neutrons are effectively superfluid, independently of the detailed choice of the interaction, cluster charge, and lattice geometry. This fraction is only slightly lower than the one obtained recently within linear response theory on top of the Bardeen-Cooper-Schrieffer approximation, and it approaches the hydrodynamic limit for strong pairing. As a consequence, it is likely that the inner crust alone can provide a sufficient superfluid angular momentum reservoir to explain pulsar glitches.
nucl-thastro-ph.HEcond-mat.quant-gasPRC(2026)·3 citations
03
Neural Network Construction of the Equation of State from Relativistic ab initio Calculations
Kangmin Chen · Xiaoying Qu · Hui Tong · Sibo Wang · Yangyang Yu
Constraining the nuclear matter equation of state (EOS) beyond saturation density is a central goal of nuclear physics and astrophysics. While the relativistic Brueckner-Hartree-Fock (RBHF) theory, an \textit{ab initio,} non-perturbative nuclear many-body theory starting from realistic interactions, accurately describes nuclear matter properties near the saturation density $ρ_{0} \approx 0.16$ fm $^{- 3}$ , its applicability is currently limited to densities up to $3 ρ_{0}$ , necessitating a reliable extrapolation to higher densities. In this work, we employ supervised machine learning to train thousands of fully connected neural networks on low-density RBHF data. By enforcing thermodynamic consistency and smoothness, we finally select a subset of 264 optimal models. These models employ the Swish activation function, which we identify as the most reliable choice for stable extrapolation after extensive testing and comparison. Using these models to extend the EOS over the full density range, we obtain the nuclear matter symmetry energy and then compute the neutron star mass-radius relation and tidal deformability, which are in a great harmony with current astronomical observations. The corresponding extrapolation uncertainty originates from the combined contributions of both the 264 optimal models and the linear regression on nuclear matter EOS, yielding a symmetry energy of $E_{sym} (5 ρ_{0}) = 136.0 \pm 52.8MeV$ , a pressure of $P (5 ρ_{0}) = 346.3 \pm 97.4 MeV/f m^{3}$ , a maximum neutron star mass of $M_{max} = 2.18 \pm 0.18 M_{⊙}$ , and a tidal deformability of $Λ_{1.4 M_{⊙}} = 532 \pm 34$ . This work establishes a general and data-driven framework to explore dense matter EOS by integrating \textit{ab initio} calculations with modern machine learning techniques.
nucl-thApJ(2026)·0 citations
04
Dissociation-driven quarkonium spin alignment in Pb--Pb collisions at $s_{NN} = 5.02$ TeV
Bhagyarathi Sahoo🇮🇳 · Captain R. Singh🇮🇳 · Raghunath Sahoo🇮🇳
The observation of spin alignment of quarkonia in ultra-relativistic heavy-ion collisions provides deep insight into the possible formation of the quark-gluon plasma (QGP). The present study investigates the spin alignment of quarkonia induced by dissociation mechanisms arising from medium effects imposed on quarkonia. We implement an effective Hamiltonian with a medium-modified color-singlet potential to incorporate the coupling of quarkonium spin with medium vorticity. This coupling gives rise to spin-dependent dissociation, which we identify as a plausible mechanism contributing to quarkonium spin alignment. Within the ambit of second-order relativistic viscous hydrodynamics, we calculate the spin-dependent decay widths of charmonium ( $J / ψ$ , $ψ$ (2S)) and bottomonium ( $Υ$ (1S), $Υ$ (2S)) in a rotating thermal medium, including collisional damping and gluonic dissociation effects. We evaluate the observable $ρ_{00}$ for Pb--Pb collisions at $s_{NN} = 5.02$ TeV as a function of transverse momentum of the quarkonia, charged particle multiplicity, and medium rotation. The results demonstrate that medium vorticity modifies the quarkonia net decay width and, as a consequence, quarkonia spin alignment gets modified. These findings suggest new directions for understanding spin transport and the microscopic dynamics of vortical QGP.
nucl-thhep-exhep-phhep-th+1PRD(2026)·1 citation
05
Quantum-inspired Bayesian probability algorithm for nuclear mass predictions
Kaizhong Tan · Jian Liu · Chuan Wang
In this study, a novel quantum-inspired Bayesian probability (QIBP) algorithm, informed by quantum dynamics, is proposed to improve the predictions of nuclear mass from theoretical models. Within the QIBP framework, residuals between the theoretical and experimental mass values are mapped into wave functions in Hilbert space. The corresponding potentials are obtained by solving the Schrödinger equation. Assuming that the residuals follow a Boltzmann distribution, the prior and likelihood probability density functions (PDFs) can be obtained from potentials. Finally, the Bayesian theorem is applied to derive the posterior PDF for estimating the target nuclear mass residuals. In global optimization, after employing the QIBP algorithm, the standard deviations of the WS4 model and the HFB model with the SLy4 parameter set are reduced from 0.273 MeV and 5.250 MeV to 0.149 MeV and 0.324 MeV, respectively. In extrapolation analysis, the QIBP algorithm also effectively improves both models, indicating robust extrapolation capability. In addition, extrapolation based on the synthetic experimental set shows that the QIBP algorithm performs well near the known region and remains effective for most nuclides toward the drip lines. Furthermore, the QIBP algorithm is applied to predict $α$ -decay energies of Ra and Es isotopes, and the shell effects manifested in these isotopes are analyzed. This study validates the feasibility of quantum machine learning in nuclear mass research and demonstrates that the proposed algorithm can accurately describe nuclear masses, with potential applications in other areas of nuclear physics.
nucl-thPRC(2026)·0 citations
06
Multi-neutron correlations in light nuclei via ab-initio lattice simulations
Shuang Zhang🇩🇪 · Serdar Elhatisari🇸🇦 · Ulf-G. Meißner🇩🇪
The quest to understand multi-neutron systems has a long history, and recent experimental efforts aim to probe candidate four-neutron configurations in neutron-rich light nuclei such as $^{8}$ He and $^{7}$ H via quasi-free knockout reactions. However, the ground-state energies of the hydrogen isotopes $^{6}$ H and $^{7}$ H are not yet well constrained, with substantial discrepancies across experimental analyses and theoretical predictions. Using ab initio nuclear lattice effective field theory with an ensemble of 282 chiral two- and three-nucleon forces, we perform a Bayesian uncertainty-quantified analysis of the ground-state energies of $^{6}$ H and $^{7}$ H. The marginal posteriors suggest single-neutron separation energy $S_{n} (^{7} H) = 0.3 5_{- 0.32}^{+ 0.32}$ MeV, which kinematically disfavors sequential decay via $^{6} H + n$ and thereby makes multi-neutron emission channels comparatively more relevant. Intrinsic densities indicate triton- and $α$ -like clusters in $^{7}$ H and $^{8}$ He, respectively. By computing two-body and reduced four-body correlation functions, we find that the valence neutrons in the surface region of these systems form compact dineutrons that predominantly organize into approximately symmetric dineutron-dineutron configurations, with only a small but non-negligible fraction assembling into more compact tetraneutron-like substructures. In $^{7}$ H, these components account for roughly 95\% and 5\% of the sampled four-neutron configurations, respectively, and $^{8}$ He exhibits a similar hierarchy. For these configurations, we also extract the corresponding spatial and angular correlation patterns among the nucleons. These results provide nuclear-structure insights into the debate surrounding four-neutron clusters and complement ongoing experimental searches for tetraneutron signatures in light nuclei.
nucl-thhep-lathep-phnucl-ex4 citations
07
Nuclear collectivity and the harmonic spectrum of two-body correlations
Jean-Paul Blaizot🇫🇷 · Giuliano Giacalone🇨🇭 · Alessandro Lovato🇮🇹
High-energy nuclear collisions have opened a new experimental method to reveal collective behavior in nuclear ground states through the lens of many-body correlations of nucleons. Using ab initio lattice and variational calculations of $^{20}$ Ne and $^{16}$ O, we study how emergent phenomena such as deformation or clustering can be identified in these systems from the dependence of their two-body density distributions on the relative azimuthal angle of nucleon pairs. A harmonic analysis of the correlation functions reveals in particular a dominant quadrupole component in $^{20}$ Ne, consistent with a bowling-pin picture, and a prominent triangular modulation in $^{16}$ O, possibly indicative of alpha-cluster correlations. Given that such structures can be accurately identified in high-energy collider experiments, these findings open a new paradigm for analyzing emergent collective behavior in atomic nuclei, relating their intrinsic shapes to the harmonic spectrum of microscopic correlations.
nucl-thhep-exhep-phnucl-ex8 citations
08
Probing the delicate balance of the spontaneous fission instability in sub-{\mu}s superheavy nucleus 252Rf
Zhen-Zhen Zhang · Hua-Lei Wang · Kui Xiao · Min-Liang Liu
Stimulated by the recent experimental discovery of the sub- $μ$ s fission nucleus $^{252}$ Rf [Phys. Rev. Lett. 134 (2025) 022501], we perform an improved configuration-constrained potential-energy-surface calculation, revealing the mechanism of intricate balance for the enhanced stability due to the high- $K$ (e.g., $K^{π} = 6^{+}$ ) isomer, possibly building on a shape isomeric state. The different deformation and coupling effects, such as triaxial $γ$ , reflection-asymmetric $β_{3}$ and high-order $β_{6}$ deformations, are discussed for both ground state and isomeric state based on the corresponding potential-energy curves along the fission valley. In particular, it is pointed out for the first time that possible multipath decay, e.g., from the high- $K$ isomeric state to those states formed between potential energy surfaces of this isomeric state and the ground state during the fission process, may reduce the nuclear lifetime and balance the fission stability. These results elucidate not only the enhanced stability of the high- $K$ isomeric state, including the inversion of stability between it and the ground state, but also the limitation of the stability increase of such an isomeric state.
nucl-thPLB(2026)·1 citation
09
Neutron star crust and outer core equation of state from chiral effective field theory with quantified uncertainties
H. Göttling🇩🇪 · L. Hoff🇩🇪 · K. Hebeler🇩🇪 · A. Schwenk🇩🇪
We study the order-by-order expansion of the energy per particle of asymmetric nuclear matter up to twice saturation density in chiral effective field theory (EFT) within a Bayesian framework. For this, we develop a two-dimensional Gaussian process (2D GP) that is trained using many-body perturbation theory results based on chiral two- and three-nucleon interactions from leading to next-to-next-to-next-to-leading order (N $^{3}$ LO). This allows for an efficient evaluation of the equation of state (EOS) and thermodynamic derivatives with EFT truncation uncertainties. After benchmarking our 2D GP against Bayesian uncertainties for pure neutron matter and symmetric matter, we study the energy per particle, pressure, and chemical potentials of neutron star matter in $β$ -equilibrium including EFT uncertainties. We investigate the phase diagram of neutron-rich matter from neutron- to proton-drip and to the uniform phase, including surface and Coulomb corrections. Based on this, we construct EOSs for the inner crust of neutron stars that are consistent with the chiral EFT results for uniform matter at N $^{3}$ LO.
nucl-thastro-ph.HEnucl-exPRC(2026)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE