Nuclear Theory·nucl-th

Tuesday·April 14, 2026

20 papers—14 primary·6 cross-listed

01
From credible shell model interactions to neutron-capture uncertainties
Oliver Gorton · Konstantinos Kravvaris
Nuclear structure theory can provide nuclear astrophysics and nuclear technologies with bound state properties and transition rates. When describing nuclear reactions, the list can be extended to include statistical properties such as nuclear level densities (NLDs) and radiative strength functions (RSFs). We present the first uncertainty-quantified neutron-capture cross section for $^{27}$ Al based on NLDs and RSFs computed with the shell model (SM). We find that the USDBUQ500 SM interaction predicts NLDs and RSFs with constant uncertainties of 6% and 9%, respectively. These, in turn, translate to a 5 to 25% uncertainty in the neutron-capture cross section, which exhibits a surprisingly non-Gaussian distribution.
nucl-th0 citations
02
$S$ -matrix calculation of $B Q$ correlation at finite baryon density
Vojtech Honek🇸🇰 · Pok Man Lo🇵🇱 · Boris Tomasik🇸🇰
We calculate the baryon number--electric charge susceptibility at non-vanishing baryo-chemical potential within the model of hadron gas where pion-nucleon interaction is accounted for by the $S$ -matrix formalism. The susceptibility is largely increased when the chemical potential grows within a phenomenologically relevant interval. The results are then evaluated along the chemical freeze-out line. We also calculate the evolution of the susceptibility in a cooling fireball by making use of the Partial Chemical Equilibrium model.
nucl-thhep-ph1 citation
03
Complementary Approach to Anisotropic Flows in Heavy-Ion Collisions
E. Dlin🇷🇺 · O. Teryaev🇷🇺
We introduce a no-reaction-plane (no-RP) method for extracting directed ($v_1$) and elliptic ($v_2$) flows in heavy-ion collisions, which eliminates the need for event-plane reconstruction. %by scanning over fixed test angles and using simple count asymmetries. The method is validated with PHSD model simulations of Au+Au collisions at $\sqrt{s_{NN}} = 9.2$ GeV at freeze-out (for impact parameters $b = 4-8$ fm). We demonstrate that the two asymmetries for each harmonic contribute equally, i.e., $\langle A_{\mathrm{ud}}^2\rangle \approx \langle A_{\mathrm{lr}}^2\rangle$ and $\langle A_1^2\rangle \approx \langle A_2^2\rangle$, so that a single asymmetry measurement suffices for a good flow estimate. Event-by-event comparisons with direct calculations using the true reaction plane yield Pearson correlation coefficients of 0.956 for $v_2$ and 0.834 for $v_1$, confirming that the no-RP method captures flow fluctuations well enough.
nucl-thhep-phnucl-ex0 citations
04
Catapult neutrons from neck snapping in fission
Jørgen Randrup · Roberto Capote · Ramona Vogt
Dynamical fission calculations show that the post-scission configurations resemble two collinear pear-shaped fragments whose juxtaposed surface bulges subside relatively quickly, as the fragments acquire smoother shapes. The associated rapid speed of the healing bulge surface may boost nucleons in the fragment to energies sufficient for emission. The present study explores this mechanism by following the fate of nucleons that are reflected off the inwards moving bulge surface. The simulations suggest that the mechanism may produce high-energy neutrons at the level of a few per cent.
nucl-th1 citation
05
Microscopic investigation of $E 2$ matrix elements in atomic nuclei -- II
Kouser Qureshie · S. P. Rouoof · J. A. Sheikh · N. Rather · S. Jehangir · G. H. Bhat · S. Frauendorf
The present work is a continuation of our earlier investigation with the primary objective to systematically calculate the $E 2$ matrix elements using the microscopic approach of the triaxial projected shell model (TPSM). In the earlier work, we studied nine nuclides of $^{72}$ Ge, $^{76}$ Ge, $^{104}$ Ru, $^{168}$ Er, $^{186}$ Os, $^{188}$ Os, $^{190}$ Os, $^{192}$ Os, and $^{194}$ Pt. In the present work six more nuclides of $^{70}$ Ge, $^{76, 78, 80, 82}$ Se, and $^{100}$ Mo have been investigated. The Coulomb excitation data has recently become available for $^{70}$ Ge and other nuclides were inadvertently omitted in our earlier investigation. It is demonstrated that TPSM approach provides a good description of the available experimental data and most of the nuclides, except for $^{76}$ Se and $^{100}$ Mo, are shown to have $γ$ soft behaviour. Further, it is demonstrated that in contrast to the predictions of the phenomenological collective model, TPSM calculations depict no clear correlation between the energy staggering pattern of the $γ$ band and the deduced shape invariant quantities using the Kumar-Cline sum rules.
nucl-th0 citations
06
Sensitivity of Neutron Star Observables to Transition Density in Hybrid Equation-of-State Models
N. K. Patra🇺🇸 · Sk Md Adil Imam🇨🇱 · Kai Zhou🇺🇸
We investigate how the transition density $\rho_{tr}$ affects hybrid constructions of the neutron-star equation of state (EoS) in which a nucleonic description at low densities is matched to a model-agnostic high-density extension based on a speed-of-sound parametrization. Using four representative nucleonic models--Taylor expansion, $\frac{n}{3}$ expansion, Skyrme, and relativistic mean-field--built from identical nuclear matter parameters, we isolate the impact of the low-density EoS and the transition density on neutron star observables. We find that, within the present smooth-matching prescription, neutron star properties such as radii and tidal deformabilities retain significant sensitivity to the choice of low-density EoS for commonly adopted transition densities around $\rho_{tr} \approx 2\rho_0$, even when the same high-density parametrization is employed. This residual dependence arises from differences in the matching conditions at $\rho_{tr}$, which propagate into the high-density extension, so different low-density inputs lead to different effective high-density EoSs. These findings are robust across two distinct speed-of-sound parametrizations. Quantitatively, the model spread in radius and tidal deformability at $1.4 M_{⊙}$ exceeds the current observational uncertainty by factors of $\sim 1.8$ and $\sim 1.4$ at $ρ_{tr} \approx 2 ρ_{0}$ , whereas these factors reduce to $\sim 1.05$ and $\sim 0.4$ at $ρ_{tr} = ρ_{0}$ . Lowering the transition density, therefore, systematically diminishes the spread among models and leads to more consistent predictions. Our results demonstrate that the widely used choice $\rho_{tr} \approx 2\rho_0$ does not guarantee model independence in hybrid EoS constructions, and should be treated as an explicit source of systematic uncertainty when inferring dense matter properties from neutron star observations.
nucl-thastro-ph.HEastro-ph.SRgr-qc+1PRD(2026)·0 citations
07
Nonlinear response of flow harmonics in Gubser flow with participant-reaction planes mismatch
Xiang Ren🇨🇳 · Jin-Yu Hu🇨🇳 · Hao-jie Xu🇨🇳 · Shi Pu🇨🇳
We investigate the nonlinear response of flow harmonics $v_{2}, v_{4}$ to initial-state eccentricities $ϵ_{2}, ϵ_{4}$ within the Gubser-flow framework. By extending the perturbative solutions of Gubser flow, we derive analytic nonlinear response relations connecting the eccentricities $ϵ_{2}, ϵ_{4}$ to the flow harmonics $v_{2}, v_{4}$ . Our results reproduce the well-known result $v_{4} / v_{2}^{2} \to 1/2$ in large transverse momentum $p_{T}$ limit. Furthermore, we study the effects of a mismatch between the participant and reaction planes. We find that the conventional nonlinear response coefficients acquire an additional factor determined by the participant-plane angles, which is often approximated as statistical noise driven by event-by-event fluctuations. This factor can modify both the strength but even the sign of the effective nonlinear response coefficient, making it sensitive to the initial configuration of the colliding nuclei. Our study provides new analytical insight into the origin of collective phenomena in relativistic heavy-ion collisions.
nucl-thhep-phnucl-exPRD(2026)·2 citations
08
Extended Variable Phase Method for Spin-1/2 Correlation Functions
Renjie Zou · Sheng Xiao · Zhi Qin · Zhigang Xiao
We have developed a systematic approach to calculate the correlation function for spin-1/2 particles, incorporating both central and noncentral components of the interparticle interaction. This is achieved by extending the variable phase method to accommodate noncentral potentials and numerically solving the Schrödinger equation. Within this framework, the partial-wave contributions to the nucleon-nucleon correlation functions adopting the Reid soft-core potential are evaluated. The resulting correlation functions are then compared for Gaussian sources of different sizes.
nucl-thPRC(2026)·0 citations
09
Inclusive breakup reactions with non-spectator fragments: Generalization of the IAV sum rules
Jin Lei
The Ichimura-Austern-Vincent (IAV) sum rule formalism for inclusive breakup reactions $a + A \to b + anything$ treats the detected fragment $b$ as a spectator by replacing its interaction with the target by an optical potential. This assumption becomes questionable when $b$ is a loosely bound composite particle such as a deuteron. I derive a generalization that removes the spectator approximation and retains $b$ 's internal degrees of freedom, providing state-resolved inclusive cross sections. Within the DWBA, all non-spectator effects enter through the source function via the operator $V_{b A} - U_{b A}$ . The exact sum rule involves the full $x + A$ resolvent $(E_{x, 0}^{+} - H_{x A})^{- 1}$ , while a single-channel IAV-like expression is recovered only when the explicit target dependence of $V_{b A}$ is neglected; post-prior equivalence is preserved in both cases. A key conceptual finding is that the standard IAV result for structureless $b$ corresponds, under closure, to the \emph{total} inclusive cross section summed over all of $b$ 's internal states, rather than the cross section for $b$ in a specific state. An operator-level estimate for $b = d$ on $^{208} Pb$ shows that the non-spectator correction is not a small perturbation at the nuclear surface. The present work is purely formal: it establishes the theoretical framework and identifies the relevant operators, while quantitative assessment of the cross-section impact awaits a full numerical evaluation of the source integrals.
nucl-thPRC(2026)·1 citation
10
$Δ l = 1$ coupling of single-particle orbitals in octupole deformed nuclei
XuDong Wang · Bin Qi · Shouyu Wang · Chen Liu
Conventionally, octupole deformation in nuclei has been attributed to strong $Δ l = 3$ couplings between opposite-parity single-particle orbitals. In this work, we demonstrate that the often-overlooked $Δ l = 1$ mode also plays an important role. Taking orbitals near the octupole magic number $N = 134$ as a benchmark, we systematically evaluate the $Δ l = 1$ and $Δ l = 3$ mixing ratios of the wave functions within the Nilsson model, interpreting the trends through matrix elements of the deformed potential. We introduce component-resolved single-particle octupole energy contributions, based on the Hellmann--Feynman relation, to quantify the contributions of each $(Δ l, Δ j)$ coupling. Furthermore, the impact of $Δ l = 1$ coupling on the rotational structure is demonstrated via particle-rotor model calculations for $^{221}$ Ra and $^{223}$ Th. Our work suggests that $Δ l = 1$ and $Δ l = 3$ octupole couplings act synergistically in driving reflection asymmetry, necessitating a revised paradigm for understanding octupole correlation.
nucl-thPRC(2026)·0 citations
11
Emulator-Assisted Nuclear DFT Inference and Its Consequences for the Structure of Neutron Stars
Pietro Klausner🇫🇷 · Marco Antonelli🇫🇷 · Gianluca Colò🇮🇹 · Francesca Gulminelli🇫🇷 · Xavier Roca-Maza🇮🇹 · Enrico Vigezzi🇮🇹
Nuclear density functional theory provides a unified description of finite nuclei and bulk nuclear matter, and is widely used to model the neutron star equation of state. However, extrapolations to supra-saturation densities require a quantified treatment of uncertainties arising from parameter estimation and functional choices. We present an updated Bayesian inference of a Skyrme energy density functional augmented by a flexible meta-model density dependence at high density. Nuclear observables are computed using a Gaussian emulator of the publicly available Milano HFBCS-QRPA code, enabling efficient exploration of a high-dimensional parameter space. Relative to previous analyses, we extend the calibration set with isospin-sensitive data, including masses and charge radii along selected Ca and Sn isotopic chains, and updated constraints from giant monopole resonances. The resulting posteriors are further constrained by \emph{ab initio} neutron-matter calculations and astrophysical observations, including recent NICER measurements, yielding consistent crust and core properties of catalyzed NS compatible with current constraints. Bulk nuclear-matter parameters are well approximated by a multivariate Gaussian with covariance matrix provided for direct reuse, while several finite-nucleus parameters exhibit pronounced non-Gaussianity.
nucl-thastro-ph.HE0 citations
12
Improved quasiparticle nuclear Hamiltonians for quantum computing
Emanuele Costa🇪🇸 · Javier Menendez🇪🇸
Quantum computing is increasingly offering concrete solutions toward the simulation of nuclear structure, with the potential to overcome the exponential scaling that limits classical diagonalization methods in large spaces. A particularly efficient encoding scheme, based on collective like-nucleon pairing modes, reduces the qubit requirements by half and avoids the non-local operator strings of standard fermion-to-qubit mappings. While this quasiparticle framework provides accurate results for semimagic nuclei, it does not adequately describe open-shell systems where proton-neutron correlations become important. In this work, we apply Brillouin-Wigner perturbation theory to systematically improve the quasiparticle description of open-shell nuclei in the $s d$ shell, reaching an energy relative error below $0.2%$ compared to the nuclear shell model. Furthermore, to make the effective Hamiltonian suitable for quantum simulation, we introduce a mean-field Hartree-Fock approximation of the non-quasiparticle resolvent, achieving ground-state energies typically within $2%$ of the exact shell-model result. This represents a systematic improvement over the bare quasiparticle Hamiltonian while remaining within the reach of near-term quantum devices.
nucl-thquant-phPRC(2026)·0 citations
13
Impact of Effective Nucleon Mass and Multineutron States on the Equation of State for Core-Collapse Supernovae
Tatsuya Matsuki · Shun Furusawa · Kohsuke Sumiyoshi · Hong Shen · Katsuhiko Suzuki
In this study, we investigate the impact of effective nucleon mass and the existence of the dineutron $(^{2} n)$ and the tetraneutron $(^{4} n)$ on the thermodynamic properties and nuclear compositions by constructing new equations of state. Our results indicate that the model with a larger effective nucleon mass slightly alters the nuclear composition in neutron-rich environments primarily due to differences in the symmetry energy: the mass fractions of unbound neutrons, protons, and heavy nuclei increase. The impact on the thermodynamic properties is negligible, except for the chemical potentials. On the other hand, multineutron states become prominent at high densities in neutron-rich environments, leading to a substantial reduction in the unbound neutron fraction. This depletion lowers the chemical potential of unbound neutrons, which in turn reduces the abundance of neutron-rich nuclei. Consequently, the number of unbound protons increases, leading to a corresponding rise in proton chemical potential. These shifts in chemical potentials promote the formation of heavy nuclei with larger mass and atomic numbers. Ultimately, this compositional shift results in a lower free energy, primarily driven by the emergence of these heavy nuclei.
nucl-thPRC(2026)·1 citation
14
Resonances extracted in truncated partial-wave analysis are effective mixtures of angular momenta (Possible implications for Höhler's clustering)
A. Švarc
In truncated partial-wave analysis one fits observables, not amplitudes, and the relevant observables are bilinear in the amplitudes. For angle-dependent observables from which partial-wave content is inferred, truncation therefore does more than simply discard higher partial waves. The extracted lower partial waves are determined by a coupled nonlinear fit and need not be direct projections of the corresponding quantities in the full non-truncated problem. Instead, truncation reshuffles pole-bearing content among partial waves, including the nominally retained lower ones, so that a resonance contribution associated with one exact angular-momentum sector can reappear in several extracted partial waves and lose a unique angular-momentum assignment. We demonstrate this explicitly in a minimal scalar toy model, where a Hermitian bilinear represented by a Legendre series truncated at order 2 is fitted by another series truncated at order 1. Even in this simplest case, the fitted low-order coefficients depend on bilinear combinations involving higher-order parts of the original amplitude. Resonance-related quantities extracted from such a truncated analysis should therefore not, in general, be interpreted as resonances with definite angular momentum. We then discuss a possible phenomenological consequence for Höhler's observation that resonance poles assigned to different partial waves in $π N$ scattering tend to cluster near a few common points in the complex energy plane. If the extracted pole-bearing quantities are effective mixtures of several angular-momentum sectors, the inferred spectrum can naturally exhibit cross-wave correlations. In this sense, truncation provides a plausible contribution to Höhler-type clustering.
nucl-thNPA(2026)·1 citation

Affiliations

first authorsco-authorsvia INSPIRE