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
10
Achieving angular-momentum conservation with physics-informed neural networks in computational relativistic spin hydrodynamics
Hidefumi Matsuda🇨🇳 · Koichi Hattori🇨🇳 · Koichi Murase🇯🇵
We propose physics-informed neural networks (PINNs) as a numerical solver for relativistic spin hydrodynamics and demonstrate that the total angular momentum, i.e., the sum of orbital and spin angular momentum, is accurately conserved throughout the fluid evolution by imposing the conservation law directly in the loss function as a training target. This enables controlled numerical studies of the mutual conversion between spin and orbital angular momentum, a central feature of relativistic spin hydrodynamics driven by the rotational viscous effect. We present two physical scenarios with a rotating fluid confined in a cylindrical container: one case in which initial orbital angular momentum is converted into spin angular momentum in analogy with the Barnett effect, and the opposite case in which initial spin angular momentum is converted into orbital angular momentum in analogy with the Einstein-de Haas effect. We investigate these conversion processes governed by the rotational viscous effect by analyzing the spacetime profiles of thermal vorticity and spin potential. Our PINNs-based framework provides the first numerical evidence for spin-orbit angular momentum conversion with fully nonlinear computational relativistic spin hydrodynamics.
↳ physics.flu-dyngr-qchep-phnucl-th+13 citations
11
Constrained Gaussian-process bridge prior for neutron-star equation-of-state inference
Tyler Gorda🇺🇸 · Oleg Komoltsev🇩🇪 · Aleksi Kurkela🇳🇴 · Eirik Sunde🇳🇴
We set forth a new method for generating model-agnostic, nonparametric priors for neutron star equation-of-state inference that are stable, causal and thermodynamically consistent by construction. This generalizes Gaussian processes to include global thermodynamic constraints, specifically allowing the inclusion of any number of training points in the form $(μ, n, p)$ while retaining thermodynamic consistency between them. The method is based on constructing constrained Gaussian-process bridges, whose correlation properties can be tuned at will allowing flexibility between a conservative prior and a theory-informed prior. The method does not require any shooting to obey multiple constraints and provides an efficient and informed way to include both chiral effective field theory and perturbative quantum chromodynamics constraints within the same framework.
↳ astro-ph.HEhep-phnucl-thApJ(2026)·11 citations
12
Quantum simulation of real-time current correlators and DIS-inspired observables in the Schwinger model
Kazuki Ikeda🇺🇸 · Zhong-Bo Kang🇺🇸 · Dmitri E. Kharzeev🇺🇸 · Wenyang Qian🇪🇸
Hadronic tensors encode the nonperturbative structure of hadrons probed in deep inelastic scattering (DIS), yet their direct evaluation requires real-time evolution that presents a challenge for traditional Euclidean lattice approaches. In this work, we present the first quantum simulation of real-time hadronic current-current correlators in a confining gauge theory, from which DIS-inspired structure functions are extracted as a proof-of-principle demonstration in the Schwinger model, i.e (1+1)-dimensional QED. Using two complementary quantum-simulation strategies -- quantum-circuit and tensor-network methods -- we compute the real-time current-current correlator directly on the lattice and validate our results against exact diagonalization where applicable. From this correlator, we compute the hadronic tensor and determine the longitudinal structure function, the sole nonvanishing DIS observable in two space-time dimensions. Our study demonstrates that quantum simulation offers a viable complementary pathway towards the evaluation of real-time observables relevant for hadronic structure. It also provides a foundation for extending the calculations from Schwinger model to other gauge theories.
↳ hep-phhep-latnucl-thquant-phJHEP(2026)·4 citations
13
Collapse of Coulomb Bound States of Vector Bosons
V.V. Flambaum🇦🇺 · H. B. Tran Tan🇺🇸
Charged spin 1 (vector) particles behave very differently from electrons or scalars in a Coulomb field. For an infinitely heavy point-like nucleus their bound state wave functions fall to the centre, and embedding the system in a renormalisable electroweak-type theory does not remedy this short-distance pathology. We therefore solve the pure Coulomb problem for a finite nuclear radius $R$ and recover the point nucleus limit by letting $R \to 0$ . This approach allows us to include the crucial Upsilon term in the wave equations, which for the point-like nucleus is proportional to delta(r) and was ignored in the previous calculations of the energy spectrum. Several unusual effects emerge: (i) The Upsilon term supports a tower of states located mainly inside the nucleus. As R -> 0 their number diverges, most lying in the negative energy continuum (energy epsilon < - m c^2). They trigger vacuum breakdown - particle-antiparticle pair creation that ultimately screens the nuclear charge. (ii) Ordinary Sommerfeld-like states (with binding energy smaller m c^2) persist, but a finite fraction of each wave function leaks into the nucleus, even as R -> 0. (iii) Charge density of a negatively charged vector particle changes sign in a vicinity of the nucleus and becomes positive charge density, whereas the Upsilon term ensures its density inside the nucleus remains negative. (iv) For weak coupling, Z alpha << 1, yet with mR <Z alpha, the non-relativistic solution differs qualitatively from Schrodinger theory despite binding energies are well below m c^2; agreement is recovered only when Z alpha << mR. These phenomena highlight the distinctive and subtle behaviour of spin-1 particles in the Coulomb field.
↳ hep-phnucl-thphysics.atom-phPRD(2026)·0 citations
14
Emergent chiral spin symmetry, non-perturbative dynamics and thermoparticles in hot QCD
Owe Philipsen🇩🇪
Several non-perturbative results for hot QCD are challenging some aspects of the phase diagram and its associated degrees of freedom which were previously believed to be well understood. With increasing temperature, the chiral crossover is followed by an intermediate region with an approximate chiral spin symmetry larger than chiral symmetry, in which pseudo-scalar mesons continue to exist as hadron-like excitations, before at some higher temperature the expected chiral symmetry is recovered. By testing general formal considerations against lattice data, it can be shown that thermally modified versions of stable vacuum particles, so-called thermoparticles, form the constituents of thermal quantum field theories, with properties quite different from what is expected perturbatively. This ``viewpoint'' aims to raise broader and, in particular, phenomenological interest in these directions.
↳ hep-phhep-latnucl-thEPJA(2026)·1 citation
15
Hydrodynamic Short-Range Correlations from Boltzmann-Langevin Equation
Li Yan🇨🇳 · Derek Teaney🇺🇸
We investigate hydrodynamic contributions to short-range two-particle correlations in relativistic heavy-ion collisions using the Boltzmann-Langevin equation. We derive and solve the transport equation for equal-time two-point correlations, obtaining both local and non-local contributions that scale with transport coefficients. The non-local correlations emerging from 2-to-2 scattering dynamics provide a hydrodynamic signature in short-range correlation measurements.
↳ hep-phnucl-exnucl-thEPJ Web Conf.(2026)·0 citations
16
Measurement of Fifth- and Sixth-Order Fluctuations of (Net-)proton Number in Au+Au Collisions from Phase II of the Beam Energy Scan Program at RHIC
The STAR Collaboration
We report high-statistics measurements of fifth- and sixth-order factorial cumulants and cumulant ratios of (net-)proton multiplicity distributions in Au+Au collisions at $s_{N N} = 7.7$ --27 GeV, using data from the STAR experiment collected during the Beam Energy Scan Phase~II at RHIC. Protons and antiprotons are identified at midrapidity ( $∣ y ∣ < 0.5$ ) with transverse momentum $0.4 < p_{T} < 2.0$ GeV/ $c$ . The proton factorial cumulants $κ_{4}$ , $κ_{5}$ , and $κ_{6}$ increase with order but exhibit no sign alternation within current uncertainties, offering no evidence for a two-component structure in the proton multiplicity distribution, as might be expected near a first-order phase transition. The cumulant ratios $C_{5} / C_{1}$ and $C_{6} / C_{2}$ fluctuate around zero in collisions at 0--40\% centrality. The results are consistent with both the negative predictions from lattice QCD (LQCD) and the positive trends obtained from the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model. At $s_{N N} ≳ 27$ GeV, the $C_{4} / C_{2}$ and $C_{5} / C_{1}$ results are compatible with predictions from lattice QCD, functional renormalization group (FRG), and hadron resonance gas (HRG) models, while UrQMD describes the data better at lower energies. These measurements place constraints on baryon number fluctuations and offer valuable insights into the QCD phase structure.
↳ nucl-exhep-exhep-lathep-ph+1PRC(2026)·2 citations
17
Strong model-agnostic constraints for twin-star solutions
Sofia Blomqvist🇫🇮 · Christian Ecker🇩🇪 · Tyler Gorda🇺🇸 · Aleksi Vuorinen🇫🇮
We perform a model-agnostic Bayesian analysis of the neutron-star-matter equation of state (EoS), using known ab-initio constraints and astrophysical observations to limit its behavior at intermediate densities. Permitting explicit first-order phase transitions allows us to systematically search for twin-star solutions, i.e. the existence of stars degenerate in mass but differing in radius. We find that current observational constraints exclude all but two classes of twin stars. The first is characterized by a first-order transition occurring at a very low density, where the material properties of the system either stay largely intact or move away from the conformal limit. In the second, more interesting class, the discontinuity in the mass-radius curve emerges after a rapid crossover transition at a significantly higher density, with the speed of sound exhibiting two sharp peaks at distinct densities. Since neither class shows clear conformalization upon entering the second branch, the standard twin-star scenario linking the mass-radius discontinuity to deconfinement can be firmly ruled out, while even the remaining solutions -- disfavored by per-mille Bayes factors and in tension with theoretical bounds -- are likely to be excluded in the future.
↳ astro-ph.HEhep-phnucl-thPRD(2026)·9 citations
18
Trigonometric continuous-variable gates and hybrid quantum simulations of the sine-Gordon model
Tommaso Rainaldi🇺🇸 · Victor Ale🇺🇸 · Matt Grau🇺🇸 · Dmitri Kharzeev🇺🇸 · Enrique Rico🇨🇭 · Felix Ringer🇺🇸 · Pubasha Shome🇺🇸 · George Siopsis🇺🇸
Hybrid qubit-qumode quantum computing platforms provide a natural setting for simulating interacting bosonic quantum field theories. However, existing continuous-variable gate constructions rely predominantly on polynomial functions of canonical quadratures. In this work, we introduce a complementary universality paradigm based on trigonometric continuous-variable gates, which enable a Fourier-like representation of bosonic operators and are particularly well suited for periodic and non-perturbative interactions. We present a deterministic ancilla-based method for implementing unitary and non-unitary trigonometric gates whose arguments are arbitrary Hermitian functions of qumode quadratures. As a concrete application, we develop a hybrid qubit-qumode quantum simulation of the lattice sine-Gordon model. Using these gates, we prepare ground states via quantum imaginary-time evolution, simulate real-time dynamics, compute time-dependent vertex two-point correlation functions, and extract quantum kink profiles under topological boundary conditions. Our results demonstrate that trigonometric continuous-variable gates provide a physically natural framework for simulating interacting field theories on near-term hybrid quantum hardware, while establishing a parallel route to universality beyond polynomial gate constructions. We expect that the trigonometric gates introduced here to find broader applications, including quantum simulations of condensed matter systems, quantum chemistry, and biological models.
↳ quant-phhep-lathep-phnucl-thJHEP(2026)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE