Nuclear Theory·nucl-th

Wed·Oct 7, 2026Wednesday·October 7, 2026

13 papers—5 primary·8 cross-listed

01
Radii and Scaling Relations of Dark-Matter-Admixed Neutron Stars
Zhi-yao Li · Wei-zhou Jiang · Dian Sun
The radius of a neutron star is closely related to the equation of state (EOS) of asymmetric nuclear matter, particularly to the nuclear symmetry energy. At fixed stellar mass, the neutron-star radius and the nuclear-matter pressure near saturation density approximately satisfy a pressure--radius (R-P) scaling relation, linking stellar geometry to strong-interaction matter. In the presence of dark matter (DM), changes in the stellar geometry can modify this relation. We investigate how GeV- and sub-GeV-scale DM affects the R-P relation in DM-admixed neutron stars (DANSs) within a gravity-only two-fluid framework. We extend the Buchdahl analytic solution to a two-fluid configuration to demonstrate this scaling and then use 21 nuclear EOSs to fit the relation $R_{NM} = C ˉ P_{NM}^{η}$ for $1 M_{⊙}$ and $1.4 M_{⊙}$ DANSs. The exponent $η$ and coefficient $C ˉ$ jointly quantify the DM-induced modification and depend on the DM particle mass, stellar DM content, and self-interaction strength. For bosonic DM, changes in $η$ and $C ˉ$ occur mainly in the sub-GeV range, whereas significant fermionic-DM effects persist up to about 1.5 GeV. Increasing the DM content or strengthening a repulsive self-interaction generally increases $η$ and decreases $C ˉ$ . The modified R-P relation therefore encodes information about the DM particle mass, abundance, and self-interaction, and affect the extraction of the nuclear EOS from celestial observations. At DM masses of several hundred MeV, both fermionic and bosonic DM can also produce DM-dominated low-mass ( $1 M_{⊙}$ ) DANSs with large radial extensions, for which the conventional scaling relation ceases to apply.
nucl-th
02
Influence of nuclear matter properties on heavy-ion sub-barrier fusion reactions
Ki-Seok Choi · Hana Gil · Kouichi Hagino · W. Y. So · Chang Ho Hyun · K. S. Kim
Interactions between two nuclei in nuclear reactions are calculated by applying the energy density method to nuclear energy density functionals. We particularly focus on the effects of nuclear mat- ter properties on fusion reactions by using the Korea-IBS-Daegu-SKKU (KIDS) density functional. Uncertainty of the equation of state in symmetric nuclear matter is accounted for by using different values of the incompressibility and the effect is explored with the 40Ca+40Ca system. Though not prominent, a systematic dependence on the incompressibility can be inferred from the fusion cross sections. The effect of asymmetric nuclear matter is described by adopting the symmetry energy parameters that are consistent with the neutron star data, but still have large uncertainties. In the application to the 48Ca+48Ca and 16O+208Pb systems, we observe a systematic dependence on the stiffness of the symmetry energy. We also consider the uncertainty of the effective mass of the nucleon in nuclear medium. We employ models that have isoscalar and isovector effective masses varying from minimum to maximum values in the allowed ranges. Contrary to incompressibility and symmetry energy, fusion cross sections are insensitive to the isoscalar and isovector effective masses. Without any phenomenological adjustment or modification of the model, fusion processes are described accurately by applying the interaction potentials derived from nuclear structure mod- els
nucl-th
03
One-nucleon intermediate-state contribution to the pion-coupled four-quark condensate in the $N$ -- $J / ψ$ interaction
Seokwoo Yeo · Philipp Gubler · Su Houng Lee
The density dependence of four-quark condensates is a major source of uncertainty in operator product expansion analyses of hadrons in nuclear matter. Their determination is particularly relevant to the $N$ -- $J / ψ$ interaction, whose long-range attraction appears to be well described by two-pion exchange in lattice QCD. We evaluate the pion-coupled four-quark condensates using one-nucleon intermediate-state insertions and incorporate them into the QCD sum rule analysis for the $J / ψ$ meson in nuclear matter. At normal nuclear matter density, we find a mass shift of $- 1.75$ MeV, which is of the same order as the approximately $- 5$ MeV attraction inferred from a two-pion exchange potential fitted to lattice QCD results. A previous factorization-based treatment required the introduction of unnaturally large phenomenological parameters to obtain a comparable shift. Our result shows that one-nucleon intermediate states provide a significant contribution to the in-medium four-quark condensates and improve the connection between the operator product expansion and the long-range $N$ -- $J / ψ$ interaction.
nucl-thhep-th
04
Probing alternating-parity bands in even-even nuclei within an axial quadrupole-octupole-hexadecapole collective model
M.Chabab · A.El Batoul · L.El Ouaourti
An analytic quadrupole octupole hexadecapole (QOH) axially symmetric model is used to provide a coherent framework for describing both octupole vibrations and octupole deformations in even-even nuclei. The model offers analytical solutions for the energy spectra and electric E1, E2 and E3 transition probabilities. The spectroscopic features are governed by three physically meaningful parameters: the stiffness constant $c_{2}$ , the hexadecapole deformation parameter $ϕ_{02}$ , and the sextic potential parameter $α$ , directly linked to $ϕ_{01}^{π}$ which represents the interplay between the quadrupole and octupole deformations for both even and odd angular momentum states. The model is applied across a broad range of nuclei including Ra, Th, Sm, Ba, U, Gd, Nd, Rn, Pu, Xe, and Ce isotopes, effectively capturing the characteristic properties of alternating parity bands. Detailed calculations of E1, E2, and E3 transition matrix elements have been performed for $^{220, 222}$ Rn, $^{222, 224, 228}$ Ra, and $^{144, 146}$ Ba yielding results in good agreement with available experimental data.
nucl-thEur. Phys. J. A 62, 118 (2026)
05
The Fock representation of the Coulomb interaction. II. Three-body bound states
M. M. Nishonov
The Fock representation of the unscreened Coulomb interaction, a block of separable terms with analytic form factors and strengths, is included in the momentum-space Faddeev kernel of three-body bound states beside the separable nuclear terms. A bound-state kernel evaluates every pair interaction at negative pair energies, where the representation is exact and convergent, so the Coulomb force enters without a screening radius and without a limiting procedure. With this representation the $^{3}$ H-- $^{3}$ He splitting of the CD~Bonn potential is in very good agreement with the exact Faddeev result; in the $S$ -wave model space the Coulomb-distorted form factors give about half the Fock value. The Feshbach--Schur projection of the Pauli-forbidden states acts on the forbidden eigenstates of the nuclear-plus-Coulomb pair Hamiltonian, the Coulomb-dressed states obtained inside the extended separable problem, as the eigenstate condition requires. The Coulomb displacements of the cluster-model states of $^{6}$ Li, $^{9}$ Be and $^{12}$ C and of the $^{9}$ Be-- $^{9}$ B mirror pair are given. The eigenstate condition is tested in $^{9}$ Be and $^{12}$ C by replacing the Coulomb-dressed forbidden states with those of the Coulomb-subtracted interaction and with the oscillator functions of the orthogonality-condition model.
nucl-th
06
Radial Modes of Hot Neutrino-Trapped Hybrid Stars
Peter B. Rau · Andrea Sabatucci · Armen Sedrakian
We study the fundamental radial oscillation mode of hot hadronic and hybrid stars under conditions relevant to proto-neutron stars and neutron-star merger remnants. The stellar backgrounds are constructed from finite-temperature equations of state with a covariant density functional for hadronic matter and three-flavor 2SC quark matter at high density. We consider two isentropic configurations in both neutrino-transparent matter and with trapped electron neutrinos at fixed electron-lepton fraction. For trapped matter we compare a Gibbs-type construction with global electron-lepton-number conservation to a locally constrained Maxwell-type prescription; in both cases the fixed-entropy stellar equation of state contains an extended coexistence region and no sharp interface requiring conversion rate-dependent junction conditions. We find that the fundamental radial frequency follows the corresponding purely hadronic sequence up to the onset of deconfinement and then decreases relative to it. Neutrino trapping shifts this dynamical signature to larger stellar masses and central pressures, reflecting the delayed appearance of quark matter. The Maxwell-type prescription moves the onset of deconfinement to still higher central pressure and produces a more rapid decrease of the mode frequency near the stability limit. We quantify the deconfinement effect through the fractional frequency shift between hybrid and hadronic stars at equal gravitational mass. These results show that the fundamental radial mode provides a sensitive dynamical probe of the interplay among entropy, lepton trapping, phase-transition construction, and quark deconfinement in hot compact stars.
↳ astro-ph.HEnucl-th
07
Chromatic Gravitational-Wave Tests of Dirac-Induced Torsion in Quadratic Einstein--Cartan Gravity: Nanohertz PTA Null Signatures
Zhi-Fu Gao · Biao-Peng Li · Na Wang · Hui Wang · Guo-Qiang Jin · Zhoujian Cao · Luiz C. Garcia de Andrade
We derive a conditional result for leading tensor propagation in Einstein--Cartan--Dirac gravity with the parity-even invariant $ζ T_{λ μν} T^{λ μν}$ and algebraic torsion sourced by a coarse-grained fermionic axial current. On a spatially flat, homogeneous, and isotropic background, eliminating the nondynamical Lorentz connection yields the Einstein--Hilbert transverse-traceless (TT) action at leading two-derivative order if the matter state obeys an explicit factorized mean-field closure: the connected contribution to $⟨ J_{5 μ} J_{5}^{μ} ⟩$ is set to zero, the factorized scalar $J ˉ_{5 μ} J ˉ_{5}^{μ}$ has vanishing first- and second-order TT response, and intrinsic TT anisotropic stress vanishes. Under these conditions, $Q_{T} = M_{Pl}^{2}$ , the tensor speed is luminal, and the local dispersion relation is $ω^{2} = k_{phys}^{2}$ , with no leading propagation-induced polarization splitting. The contribution is a model-specific constrained TT-Hessian calculation for this invariant that retains the auxiliary-connection response and states the closure needed for the $ζ$ -dependent terms to cancel. The connected-current TT response of a general fermionic state is not evaluated; this is therefore a conditional result, not a general Einstein--Cartan no-go theorem. The coupling $ζ$ remains in the axial--axial fermion contact interaction. We define null-test observables and a covariance-weighted statistic for future pulsar-timing-array (PTA) likelihood analyses. Published NANOGrav 15-year harmonic posteriors and the public 2026 collaboration preprint serve only as consistency checks: we perform no new time-of-arrival (TOA)-level likelihood or evidence calculation, and these data do not directly constrain $ζ$ .
↳ gr-qchep-exnucl-th
08
Born-Oppenheimer Effective Field Theory as a unified framework for all the XYZ exotics
Tommaso Scirpa
We discuss some recent applications of the Born-Oppenheimer effective field theory (BOEFT) formalism, directly derived from QCD and grounded in scale separation and symmetries, to hadronic systems containing two heavy quarks. This formalism provides a unified description of both ordinary and exotic quarkonium states (i.e., hybrids, tetraquarks, pentaquarks, ...) dynamics via coupled Schrödinger equations, whose potentials are computable on the lattice. The aim is to unveil the elusive pattern of the XYZ exotic hadrons. Here, we apply the BOEFT formalism to the $χ_{c 1} (3872)$ , $T_{cc} (3875)^{+}$ , and their bottom counterparts. Moreover, we assess the threshold effects on the quarkonium spectrum and discuss the inclusive production cross section for $χ_{c 1} (3872)$ .
↳ hep-phhep-exhep-latnucl-th
09
Neutral Pseudoscalar Mesons, Hadron Light-by-Light Scattering, and the Muon Anomalous Magnetic Moment
Cong-Cong Ye · Yu-Chen Hu · Minghui Ding · Craig D. Roberts
Continuum Schwinger function methods\linebreak (CSM) are used to provide estimates of pseudoscalar meson pole contributions - $P = π^{0}$ , $η$ , $η^{'}$ , $η_{c}$ , $η_{b}$ - to the muon anomalous magnetic moment. The analysis framework is benchmarked via successful applications to an array of other meson and nucleon properties. It uses the leading order CSM truncation, augmented by a parametrisation of non-Abelian anomaly effects, to deliver an internally consistent treatment of all the pseudoscalar--two-photon transition form factors required to complete such a calculation. Employing those form factor predictions, the following results are obtained (units $1 0^{- 11}$ ): $a_{μ}^{π^{0}} + a_{μ}^{η} + a_{μ}^{η^{'}} = 84.3 (0.8)$ - a value lower than some other contemporary estimates; $a_{μ}^{η_{c}} = 0.82 (0.04)$ ; and a value of $a_{μ}^{η_{b}}$ that is negligible. The total contribution is $\sum_{P} a_{μ}^{P} = 85.1 (0.8) /1 0^{11}$ . Our analysis suggests that this pole contribution to $a_{μ}$ is still not known with precision better than 5\%.
↳ hep-phhep-exhep-latnucl-ex+1
10
Early galactic heavy element production - a phenomenological approach
B. Wehmeyer · D. Blaschke · F.K. Röpke · G. Röpke
The high abundances of heavy elements in early, extremely metal-poor stars is still an unsolved issue in Galactic Chemical Evolution (GCE). Standard approaches, such as mergers of neutron stars, have several difficulties, and several non-merger production channels are under discussion. Here, we suggest that pre-enriched inflow might explain the heavy elements seen in low metallicity stars in the Galaxy. To characterize the conditions of the origin of such a pre-enriched infall, we apply a heavy-element freeze-out approach. We characterize the initial distribution by Lagrange parameters which are nonequilibrium generalizations of temperature and chemical potentials. We then speculate about the origin of such a pre-enriched infall: The required nonequilibrium conditions might be found in cosmological fluctuations in the early Universe, and might be connected to the formation of primordial black holes.
↳ astro-ph.GAnucl-th
11
Comparison of pair-source and correlation-function based Lévy analyses in Ar+Sc system at SPS energies
Barnabás Pórfy
Non-Gaussian features in femtoscopic observables have been observed in high-energy collisions, yet their origin remains not fully understood. This study focuses on the phenomenological approach to femtoscopy, going beyond the Gaussian approximation by utilizing Lévy-stable source distributions. Using UrQMD simulations, three-dimensional analyses of pion sources are done in central Ar+Sc collisions, and the extracted parameters are studied as functions of transverse mass and collision energy. This analysis contributes to a hadronic baseline motivated by past and future research work in femtoscopy at the NA61/SHINE experiment. A direct methodological comparison is presented between parameters extracted from the projections of three-dimensional pair-source distribution and those obtained from the three-dimensional correlation function, reconstructed via Fast Fourier Transform.
↳ hep-phnucl-th
12
Compositeness of near-threshold exotic hadrons in systems with Coulomb and short-range interactions
Tomona Kinugawa · Tetsuo Hyodo
We study the universal properties of near-threshold $s$ -wave eigenstates in systems with Coulomb plus short-range interactions by analyzing their compositeness. Using a nonrelativistic effective field theory, we derive a relation between the compositeness of near-threshold states and the Coulomb scattering length, the Coulomb effective range, and the Bohr radius. We find that the long-range Coulomb interaction modifies the threshold behavior expected from the low-energy universality of purely short-range systems. When the Coulomb interaction is relatively weak compared with the short-range interaction, a remnant of the low-energy universality associated with the short-range interaction survives, leading to composite-dominant near-threshold eigenstates. In contrast, in the strong-Coulomb regime, this remnant disappears.
↳ hep-phnucl-th
13
Medium modification of pseudoscalar meson structure: Distribution amplitudes and parton distribution functions
Muhammad Ridwan · Parada Tobel Paraduan Hutauruk · Ahmad Jafar Arifi · Kazuo Tsushima
In this work, we present a comprehensive investigation of the in-medium properties and internal structure of pseudoscalar mesons within the light-front quark model (LFQM), employing both Gaussian and power-law (PL) wave functions. We incorporate in-medium quark properties obtained from the quark-meson coupling (QMC) model into the LFQM, thereby providing a unified description in terms of quark degrees of freedom. We investigate the distribution amplitudes (DAs) and parton distribution functions (PDFs) of $π^{\pm}$ , $K^{\pm}$ , $D^{\pm}$ , and $B^{\pm}$ mesons in symmetric nuclear matter. We find that the evolved in-medium pion DA and PDF are strongly suppressed at intermediate $x$ , indicating substantial medium-induced modifications to the meson structure. The signs and magnitudes of the modified Gegenbauer coefficients $a_{n}^{'}$ , the parameter $ξ$ , and the Mellin moments of the DAs and PDFs in nuclear matter are found to be consistent with other theoretical predictions. In particular, the second Gegenbauer coefficient of the pion DA, $a_{2}^{π}$ , increases substantially with nuclear density, from $0.096$ ( $0.057$ ) in vacuum to $0.232$ ( $0.202$ ) at normal nuclear density for the Gaussian (PL) wave function, respectively. This increase indicates a broader pion DA and an enhanced second Gegenbauer moment in the nuclear medium. We further calculate the pion PDF ratio $R_{ρ /0}^{π}$ and find that its $x$ dependence exhibits a behavior qualitatively similar to the observed European Muon Collaboration (EMC) effect, highlighting the important role of QCD evolution in shaping the medium-modified partonic structure. Finally, we compare the calculated free-space $π^{\pm}$ and $K^{\pm}$ DAs with available free-space lattice QCD results and find reasonable agreement.
↳ hep-phhep-exnucl-th