Nuclear Theory·nucl-th

Thu·Oct 15, 2026Thursday·October 15, 2026

11 papers—7 primary·4 cross-listed

01
Strange-quark-number-dependent response to partonic dynamics in baryon-rich Au+Au collisions
Di Zhao · Xun Zhu · Gao-Chan Yong
We identify a strange-quark-number-dependent hierarchy in the response to explicit partonic dynamics by comparing PHSD5.2 with its hadron--string limit in baryon-rich Au+Au collisions at $\snn = 3.0$ -- $7.2$ ~GeV. Crossing the local conversion threshold alone does not ensure a visible final-state signal: abundant-hadron flow changes little at 3--4.5~GeV, whereas the fractional yield response becomes ordered at 6.2--7.2~GeV, reaching $S_{∣ s ∣ = 1} ≃ 0.2$ -- $0.3$ , $S_{∣ s ∣ = 2} ≃ 0.65$ , and $S_{∣ s ∣ = 3} ≃ 0.93$ at 7.2~GeV. The hierarchy is consistent with an enlarged recombination phase space for strange constituents released from different pre-hadronic sources, but does not by itself establish an increase in the total $s + s ˉ$ abundance or stronger strange-quark clustering. Since $S_{X}$ is a model-defined response rather than a direct observable, matched excitation functions of $Ξ^{-} /Λ$ and $Ω^{-} /Λ$ , together with high- $m_{T}$ proton elliptic flow, provide experimentally accessible discriminants between the predicted PHSD and HSD dynamics.
nucl-thnucl-exPhys. Lett. B 882 (2026) 141031
02
Binding energies in the $0^{-+}$ and $1^{--}$ fermion--antifermion channels from the ladder Bethe-Salpeter and Schrödinger equations
Wei He · Hai-Qing Zhou
In this work, we calculate the binding energies of an equal-mass fermion--antifermion system in the $0^{-+}$ and $1^{--}$ channels from the ladder Bethe--Salpeter (BS) equation with scalar, pseudoscalar, and vector exchange. The results are compared with those of the Schrödinger equation with the corresponding leading static interaction in two regimes: pointlike massless exchange at weak coupling and finite-mass exchange with monopole form factors at stronger coupling. For the BS calculation, we use two independent numerical methods based on momentum-space integral equations and coordinate-space differential equations. The differential-equation method gives estimated relative binding-energy errors below $1 0^{- 9}$ in both regimes. For massless vector exchange in Coulomb gauge, the numerical results are consistent with the uncrossed-ladder perturbative spectrum through the $O (m α^{5})$ terms. The results for massless scalar exchange and vector exchange in Feynman gauge are consistent with the common Wick--Cutkosky expansion through order $m α^{3}$ . For finite exchange masses, the differences from the leading static Schrödinger spectra at the same masses, couplings, and form factors depend strongly on the exchange and channel. Scalar exchange gives nearly degenerate channels with much weaker binding than the Schrödinger reference. In contrast, vector exchange with only the metric term retained gives stronger binding than the Schrödinger reference in $0^{-+}$ and weaker binding in $1^{--}$ . Notably, retaining the full Proca numerator substantially increases the vector binding in both channels. Pseudoscalar exchange also supports bound states and favors $1^{--}$ , although its leading static central interaction vanishes.
nucl-thhep-ph
03
R-process nuclei in the rare-earth region above N=126 in Relativistic Hartree-Bogoliubov theory: A preponderance of shape-coexistence in nuclei
M.M. Sharma
The shell structure of nuclei beyond N=126 relevant to the third peak at A ~ 195 in r-process nuclear abundances in investigated. Within the framework of the relativistic Hartree-Bogoliubov theory in deformed space, a comparative study of the response of nuclei with three different model Lagrangians NL-SV1, SVI-2 and NL3 is made. Ground-state properties of even-even nuclei in the isotopic chains of Z=58-72 $= in t h e hi g h l y n e u t r o n - r i c h r e g i o na r e in v es t i g a t e d . A co m p a r i so n o f bin d in g e n er g i es w i t hma ss f or m u l a ss h o w s t ha t in t h ee x t r e m er e g i o n o f t h er - p r ocess p a t h, t h e R M F m o d e l S V I - 2 w i t h o u t n o n l in e a r i t i eso f s i g maan d o m e g am eso n ss h o w s an e x ce l l e n t a g r ee m e n tw i t h t h e ma ss f or m u l a H F B - 24. I t i ss h o w n t ha t ina l l t h e ab o v e L a g r an g ianm o d e l s, in t h e n e u t r o n r i c h r e g i o nb e tw ee n t h es h e l l c l os u r es N = 126 an d N = 184, t h er e i s a p r e p o n d er an ceo f n u c l i d ese x hibi t in g coe x i s t e n ceo f w e l l - d e f or m e d p r o l a t e an d o b l a t es ha p es in t h e g r o u n d s t a t e . A p r o l a t e g r o u n d s t a t e i ss h o w n t oe v o l v es m oo t h l y t o a coe x i s t in g o b l a t e g r o u n d s t a t e v iaan e a r d e g e n er a cy w i t h s u ccess i v e a dd i t i o n o f n e u t r o n s . I n d u ce d b y an o n se t o f d e f or ma t i o n f or$ N \ge 130$, nuclei approaching the r-process path are shown to exhibit enhanced stability in many isotopic chains (Z > 60). This has the effect of shifting the expected neutron drip line significantly farther into the neutron-rich region especially for the higher Z chains. Consequences of the enhanced stability, the shape co-existence and degeneracy of shapes in nuclei on the r-process nucleosynthesis are discussed.
nucl-th
04
Collective-flow signatures of bubble nuclei in intermediate-energy projectile fragmentation reactions
Ge Ren · Chun-Wang Ma · Xi-Guang Cao · Kai-Xuan Cheng · Jie Pu
Characterized by central density depletion, bubble nuclei represent an important class of exotic nuclear structures. Collective flow in the $^{40}$ Ca+ $^{9}$ Be projectile fragmentation reaction at 140 MeV/u is investigated using the extended quantum molecular dynamics (EQMD) model with a parameter on of the isoscalar monopole excitation strength $ε$ . The projectile $^{40} C a$ is initialized as a relaxed ten- $α$ cluster configuration exhibiting a bubble-like density distribution. The results reveal that increasing $ε$ modifies the density distribution and the size of the depleted central region of bubble, producing pronounced changes in fragment yields and collective flow around $ε \approx 0.5$ . Below this value, heavy-fragment production plays a significant role, while the directed flow $v_{1}$ of protons and neutrons remains predominantly negative, indicating preferential emission toward the target side. Above $ε \approx 0.5$ , enhanced expansion of the central low-density region suppresses heavy residues and drives $v_{1}$ toward positive values. In contrast, preformed $α$ clusters show different responses, reflecting their origin in the initial cluster configuration rather than solely in secondary decay. At low excitation, the cluster flow exhibits a pronounced impact-parameter dependence, whereas stronger excitation weakens cluster binding and suppresses directional anisotropy, driving the flow close to zero. The rapidity slopes of the flow coefficients also vary systematically with $ε$ , tracing changes in emission anisotropy during expansion. These findings extend traditional static descriptions by probing the dynamical evolution of exotic structures in heavy-ion reactions and the contrasting collective-flow behavior of preformed clusters and single nucleons constitutes a sensitive dynamical probe of bubble-like structures.
nucl-thnucl-ex
05
Constraining three-nucleon forces in nuclear lattice effective field theory
Serdar Elhatisari · Ulf-G. Meißner · Zhengxue Ren · Shuang Zhang
We study short-range three-nucleon forces (3NFs) in nuclear lattice effective field theory with a chiral two-nucleon interaction at N $^{3}$ LO. The one-pion-exchange ( $c_{D}$ ) and contact ( $c_{E}$ ) terms of the leading 3NF are decomposed into locally and non-locally smeared components and supplemented by partial-wave-resolved pair contacts coupled to the density of a third nucleon. We determine their coefficients from nuclear binding energies for nuclei in the mass range from $A = 3$ to $A = 40$ and neutron--alpha finite-volume energies. This allows to work out the minimal three-nucleon force that can be used for future precision studies in NLEFT.
nucl-thhep-latnucl-ex
06
Fast Monte Carlo calculation of multiple scattering in resonant neutron capture
R. M. Djilkibaev
A fast Monte Carlo code has been developed to calculate multiple neutron scattering in a sample. Good agreement with an independent Monte Carlo calculation using SAMMY is obtained for neutron capture in $^{197}$ Au over the energy range 50--300 eV. For capture following two or more scattering events, a difference is found between the direct Monte Carlo calculation and the analytical approximation in SAMMY. The computational speed allows the scattering correction to be recalculated whenever trial resonance parameters are changed during parameter estimation. The computational core is implemented in C++, while data preparation, calculation control and analysis are performed in Python. Model studies examine how Monte Carlo statistics affect the accuracy with which neutron and radiative resonance widths are recovered.
nucl-thphysics.ins-det
07
Prospects for modelling odd and odd-odd nuclei using energy density functionals
A.V. Afanasjev · B. Bally · M. Bender · J. Bonnard · J. Dobaczewski · M. Kortelainen · K. Nomura · S. Péru · N. Pillet · L.M. Robledo · R. Rodr\'ıguez-Guzmán · W. Ryssens · W. Younes
About half of particle-bound nuclei have an odd number of nucleons. About one quarter more are odd-odd, meaning they have an odd number of neutrons and an odd number of protons. In this context, it is about time to shift the 70-odd-year focus of theories using nuclear energy density functionals (EDFs) away from the remaining one-quarter of even-even nuclei. This White Paper aims to present open, unresolved problems and promising research directions in nuclear EDFs that were discussed during the 2024 ESNT workshop in Saclay, France, on ``The microscopic modelling of odd-mass and odd-odd nuclei''.
nucl-th
08
Constraints on pion parton distributions at small $x$ from leading-neutron electroproduction data
C. Yang · P. C. Barry · W. Melnitchouk · N. Sato
We revisit the extraction of parton distribution functions (PDFs) in the pion in a global QCD analysis of pion--nucleus Drell--Yan and leading-neutron (LN) electroproduction data, in view of recent suggestions that uncertainties on the pion PDFs at small parton momentum fraction $x$ are dramatically underestimated. We perform a set of controlled fits that vary the LN data coverage, PDF parametrization, and positivity constraints, determining both the PDFs and pion-nucleon splitting functions simultaneously. While the use of a restricted H1 LN data sample used by the Fantômas group is found to enlarge the PDF uncertainties and admit solutions with vanishing gluon PDFs, our global analysis provides a good description of an extended H1 and ZEUS LN database, significantly reducing the parametrization dependence and strongly disfavoring a zero gluon distribution.
↳ hep-phhep-exnucl-th
09
Excited-State Effects in Nucleon Sigma Terms from a Variational Analysis
Constantia Alexandrou · Giannis Koutsou · Yan Li · Srijit Paul · Ferenc Pittler
We investigate excited-state effects in nucleon sigma-terms in lattice QCD using twisted-mass clover-improved fermion ensembles. We study correlation functions with nucleon and multihadron nucleon- $σ$ -meson interpolating operators. The analysis is performed using three gauge ensembles, including one ensemble simulated with two degenerate light, a strange, and a charm quark with quark masses tuned to approximately their physical value. We solve the generalized eigenvalue problem that arises from the matrix of correlators and show that the three-point function for the light sigma-term obtained using the optimal linear combination of interpolating operators has substantially reduced time dependence without loss of statistical precision. We apply Laplace filtering and investigate residual excited-state contributions in the extraction of $σ_{π N}$ . Using the same optimal linear combination of correlators as for $σ_{π N}$ for the strange sigma-term we also observe suppressed excited state contributions over an extended range of source--sink time separations. For the charm sigma-term, we observe negligible time dependence within the large statistical uncertainties, and these improvements show no significant effect.
↳ hep-lathep-phnucl-th
10
Universal enhancement of the pairing gap in a dilute Fermi superfluid
Silas R. Beane · Roland C. Farrell · Cameron P. Shotwell
At zero temperature, a dilute Fermi gas with an attractive contact interaction forms a superfluid with gapped fermionic excitations. We show that the gap at weak coupling can be organized as a trans-series expansion in the interaction strength and the asymptotic Gor'kov-Melik-Barkhudarov gap. Low-energy virtual quasiparticles generate corrections that are linear in the gap with a leading coefficient nearly 25 $\times$ larger than the other known coefficients. This substantially increases the gap at intermediate densities, highlighting that systematic corrections are crucial for quantitative predictions.
↳ cond-mat.quant-gascond-mat.supr-connucl-thquant-ph
11
Evolution of multihadron fragmentation functions with nonperturbative behavior
K. Makino · T. C. Rogers
QCD calculations that use multihadron fragmentation functions usually involve multiple invariant mass scales simultaneously, with only one being the hard scale associated with an overall hard process. The other scales are associated with relative internal motion intrinsic to the fragmenting parton and the multihadron system. Nonperturbative contributions to this later type of dependence attract interest for their association with intrinsic partonic structures, but care is needed in disentangling the truly nonperturbative effects from perturbative behavior and relating the former to universal nonperturbative matrix elements. To this end, we show how to evolve collinear multihadron fragmentation functions in a way that accounts for the simultaneous presence of these extra scales. The general multihadron fragmentation functions evolve in the same way as ordinary single hadron fragmentation functions, with the dependence on the extra scales separated out. We use this to unify treatments of perturbative and nonperturbative effects in multihadron systems in a way that optimizes for interpretations focused on partonic structure.
↳ hep-phhep-thnucl-th