Nuclear Theory·nucl-th

Wednesday·June 24, 2026

11 papers—3 primary·8 cross-listed

01
[Submitted on 22 Jun 2026]
As above, so below: assessing extremeness of the neutron-star equation of state based on the unstable branch
Tyler Gorda · Oleg Komoltsev · Aleksi Kurkela · Jürgen Schaffner-Bielich
Microscopic models of neutron-star matter have been widely used in astrophysical applications. The focus of attention has been on densities up to the maximal densities reached in stable neutron stars. The possibility that the underlying model assumptions may have important implications at higher densities has not been addressed. Here, we show that the behaviour at higher densities is strongly constrained by requiring a causal, stable, and thermodynamically consistent extension to the perturbative-QCD regime. We explicitly reveal what that behaviour must be and provide a tool for constructing and visualizing such extensions. We find that purely hadronic models trusted up to the maximal central density often require radically different behaviour at higher densities from that assumed in the original model, while models with additional degrees of freedom fare better. Our analysis disfavors purely nucleonic models for describing all stable neutron stars and supports the appearance of some type of additional degrees of freedom in stable massive neutron stars.
Comments:
9 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Theory (hep-th)
arXiv:
2606.23929 [pdf]
2 citations
02
[Submitted on 23 Jun 2026]
Understanding the Intermittency Signal in RHIC-STAR Data through Modeling
Jin Wu🇨🇳 · Zhiming Li🇨🇳 · Mingmei Xu🇨🇳 · Shuyun Yang🇨🇳 · Ranran Guo🇨🇳 · Yuanfang Wu🇨🇳
Intermittency analysis provides a promising probe of scale-invariant density fluctuations near the QCD critical point. The intermittency measurements reported in the STAR BES-I data call for a quantitative assessment of the signal strength and a clearer physical understanding of its collision-energy dependence. In this work, we perform such a study for the STAR measurements using an improved hybrid UrQMD+CMC model, in which critical-like fluctuations are embedded into a realistic non-critical background through event-level, particle-level, and combined replacement schemes. By directly comparing the second-order factorial moment $Δ F_{2} (M)$ between model calculations and experimental data on a point-by-point basis, we constrain the effective critical-like contribution compatible with the STAR measurements without relying on scaling exponents. The STAR data at $s_{NN} = 7.7$ -- $27 GeV$ used for model comparison can be consistently described only by small and nearly energy-independent effective critical-like fractions. These results indicate that the current BES-I intermittency signal is weak and exhibits little collision-energy dependence, thereby favoring only a limited critical-like contribution rather than a strong critical-point-induced enhancement localized near a specific collision energy.
Comments:
10 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2606.24436 [pdf]
0 citations
03
[Submitted on 23 Jun 2026]
Mass-Dependent Non-Extensivity in Tsallis Blast-Wave Fits to Identified Hadron $p_{T}$ Spectra at RHIC and LHC
C.Y. Tsang🇺🇸 · Z. Xu🇺🇸
We analyze identified-hadron transverse-momentum spectra from STAR Au+Au and ALICE Pb+Pb collisions over $s_{N N} = 7.7$ ~GeV-- $5.02$ ~TeV using an extended Tsallis Blast-Wave (TBW) framework, which includes a non-extensivity parameter $q$ to quantify the degree of incomplete thermal equilibrium. Conventionally, either a common value of $q$ , or two separate $q$ values, one for mesons and one for baryons, are used to describe particle spectra in the TBW framework, with the latter being referred to as TBW4 in Ref.~\cite{Chen:2020zuw}. This work extends the TBW framework by studying the dependence of $q$ on different kinds of particles in detail. Fits allowing independent non-extensivity parameters $q$ for each species reveal a systematic correlation between $q$ and particle mass, except for quarkonia. Motivated by this trend, we introduce two new parameterizations: TBW5, which posits that $q$ depends linearly on particle mass, and TBW6, which allows the $q$ intercepts for mesons and baryons to differ. Across all energies and centralities considered in this study, TBW5 improves $χ^{2} / NDF$ relative to the TBW4 fit in 71\% of the datasets, while TBW6 shows improvement in 94\% of the datasets. They perform especially well in central collisions. These results demonstrate a robust mass ordering in non-equilibrium behavior at kinetic freeze-out and provide a more accurate description of hadron spectra from RHIC to LHC energies.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2606.24777 [pdf]
0 citations
04
[Submitted on 20 Jun 2026] (cross-list from hep-ph)
Analysis of Fully-Heavy and Hidden-Heavy Tetraquarks in Anisotropic Plasma Using the Generalized Fractional Derivatives
H. M. Fath-Allah🇪🇬 · M. Abu-Shady🇪🇬 · E. M. Khokha🇪🇬
Investigating the spectroscopy and thermal stability of exotic multiquark states provides crucial insights into the fundamental confinement mechanisms of quantum chromodynamics (QCD) under extreme regimes. This work presents an innovative study of the spectroscopy and dissociation of fully-heavy tetraquarks in an anisotropic plasma via the generalized fractional derivative (GFD) structure. The radial Schrödinger equation (SE) with an extended Cornell potential that includes Debye screening and plasma anisotropy into account is solved by applying the parametric generalised fractional Nikiforov-Uvarov (PGFNU) technique. The analysis of systems consisting of $cc c ˉ c ˉ$ and $bb b ˉ b ˉ$ shows that the binding potential of the systems and the dissociation energy increase with the anisotropy parameter and decrease with temperature. The fractional paradigm also shows that when the fractional orders are lower, the systems will be more strongly bound than in classical quantum mechanics. Furthermore, the mass spectra for all considered tetraquark configurations, including the $cc c ˉ c ˉ$ , $bb b ˉ b ˉ$ , $c q ˉ c q ˉ$ , and $b q ˉ b q ˉ$ systems, are calculated for both ground and excited states. These calculations were performed across both the fractional and classical regimes. The findings indicate that the GFD framework provides an effective mathematical basis for modelling hadronic systems in complex contexts, and they demonstrate significant agreement with earlier theoretical studies.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2606.23732 [pdf]
0 citations
05
[Submitted on 21 Jun 2026] (cross-list from hep-ph)
From Magnetic to Inverse Magnetic Catalysis: The Interplay of Quark and Gluon Mass Generation in Magnetic Fields
Fei Gao🇨🇳 · Kairen Huang🇨🇳 · Yi Lu🇨🇳 · Yuxin Liu🇨🇳
We analyze the effects of the magnetic field on the quark and gluon propagators within the functional QCD framework. By solving the coupled Dyson-Schwinger equations for the quark and gluon propagators, we find that the quark mass is generally enhanced in the presence of a magnetic field, leading to magnetic catalysis of the chiral condensate. Meanwhile, the magnetic field also induces an increase in the gluon screening mass. The enhancement of the gluon screening mass suppresses the quark-gluon interaction and thereby weakens the strength of dynamical chiral symmetry breaking, establishing a competing mechanism against magnetic catalysis. In particular, this enhancement of the gluon screening mass becomes dominant near the chiral phase transition, which in turn gives rise to inverse magnetic catalysis.
Comments:
8 pages, 4 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2606.23736 [pdf]
1 citation
06
[Submitted on 22 Jun 2026] (cross-list from hep-ph)
Scalar diquarks in the QCD vacuum
Hosein Gholami🇩🇪 · Ugo Mire🇩🇪 · Fabian Rennecke🇩🇪 · Bernd-Jochen Schaefer🇩🇪 · Shi Yin🇩🇪
While QCD fundamentally only depends on the values of the strong coupling and the quark masses, it exhibits a rich nonperturbative structure at low energies, where composite fields emerge as the relevant degrees of freedom. In this work, we present a first-principles framework that captures the transition from fundamental QCD to its low-energy sector in vacuum. It builds on the dynamical hadronization technique within the functional renormalization group approach to two-flavor QCD. In this framework, the low-energy constants relevant for effective models, including effective masses and coupling strengths, naturally emerge from the underlying renormalization group flow without introducing free parameters beyond those of QCD itself. We investigate the dynamical emergence of the pion, the $σ$ -meson and the scalar diquark in both imaginary and real time, and determine a set of QCD low-energy constants which can be used to fix the free parameters of models of dense quark matter with a two-flavor color superconducting phase. In particular, this includes previously unknown properties of the scalar diquark. Our results provide important microscopic input for constraining color superconducting phases, which are expected to play a key role in our understanding of dense neutron star matter.
Comments:
46 pages, 22 figures, 4 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2606.23772 [pdf]
2 citations
07
[Submitted on 22 Jun 2026] (cross-list from hep-ph)
Polarized Deep-Inelastic Scattering with Spin Correlations in Herwig 7
M.R. Masouminia🇬🇧 · A. Papaefstathiou🇺🇸 · P. Richardson🇬🇧
We investigate polarized deep-inelastic scattering (DIS) in the context of fully exclusive Monte Carlo simulations for the Electron-Ion Collider (EIC). We present a next-to-leading-order (NLO) treatment of polarized DIS in HERWIG 7 using the POWHEG matching scheme, including neutral-current $γ / Z$ exchange and charged-current scattering. We also construct a spin-correlation treatment for NLO-matched events, first by initializing the shower from the spin-density matrix of the polarized DIS Born process and then by propagating the spin-density matrix of the accepted real-emission configuration without changing the POWHEG event weight or hardest-emission choice. We validate the integrated cross sections against fixed-order calculations, use parton-level comparisons without subsequent shower evolution to isolate the accepted POWHEG real-emission kinematics, and employ shower-level observables to test the numerical importance of the Born-level and real-emission spin information. We find that the Born-level spin-density initialization can have a visible impact on shower-sensitive observables, while the additional spin information from the accepted real-emission configuration is not resolved as a robust separate effect within the independent-sample Monte Carlo precision for the longitudinally polarized observables considered here.
Comments:
55 pages, 17 figures, 6 tables. Updated shower-spin study using independent physical-helicity samples and covariance-aware uncertainties; replaced the spin-correlation figures and clarified the associated conclusions. Corrected the report number and NNLO references
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2606.23845 [pdf]
0 citations
08
[Submitted on 22 Jun 2026] (cross-list from hep-ph)
Mapping jet substructure in heavy-ion collisions with track functions
João Barata🇨🇭 · Yeonju Go🇺🇸 · Daniel Pablos🇪🇸
We investigate the dynamics of high-energy QCD cascades in heavy-ion collisions, focusing on modifications to jets' substructure induced by the presence of a quark-gluon plasma (QGP). To this end, we study the properties and scale evolution of track functions, non-perturbative objects encoding the flow of energy from an initiating parton to all charged hadrons. In contrast to the more standard fragmentation functions, these objects have a non-linear renormalization group (RG) evolution, being sensitive to the entire jet fragmentation process. Using the JEWEL and HYBRID Monte-Carlo models of jet quenching, we find that in both frameworks the higher moments and cumulants of the track functions' distributions exhibit sizable deviations from their vacuum baselines, demonstrating that medium-induced energy loss imprints itself in the in-medium jet fragmentation pattern. We find that the quantitative magnitude of these modifications differs significantly between the two models. This identifies track functions as a class of observables capable of discriminating between competing microscopic pictures of jet-medium interactions. We further examined the (in-medium) RG flows for the leading moments, which remain in qualitative agreement with the in-vacuum evolution. This provides an avenue to directly test the RG flows inside a QGP, linking heavy-ion jet measurements to basic QFT understanding of partonic branching. Finally, we comment on the feasibility and challenges associated with extracting track functions from experimental data.
Comments:
31 pages, 17 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2606.23971 [pdf]
0 citations
09
[Submitted on 23 Jun 2026] (cross-list from astro-ph.HE)
Asteroseismology of neutron stars with both hyperons and $Δ$ resonances
Hao Sun🇨🇳 · Jia-Xing Niu🇨🇳 · Yong Gao🇩🇪 · Hong-Bo Li🇨🇳 · Cheng-Jun Xia🇨🇳
Employing various relativistic energy density functionals for nucleon-nucleon interactions, we investigate the impact of hyperons and $Δ$ resonances on the frequencies of non-radial oscillations in neutron stars, where the universal coupling scheme is adopted for the $Δ$ -meson couplings. It is found that the inclusion of $Δ$ resonances is essential for neutron stars to accommodate the recent mass and radius measurements of PSR J0030+0451, PSR J0740+6620, PSR J0437-4715, PSR J0614-3329, and HESS J1731-347. As $Δ$ resonances start to emerge in neutron stars' inner core, the $g$ -mode oscillation energy becomes concentrated within the $Δ$ -admixed region, leading to a sharp increase in the $g$ -mode frequency. We also examine the $f$ -mode and $p$ -mode oscillations and find that the impact of $Δ$ resonances on these modes is less pronounced than the $g$ -modes. The oscillation frequencies calculated in the Cowling approximation are then compared with those from full general relativity, confirming that the Cowling approximation introduces an error of approximately 20\% for the $f$ -modes and within 10\% for the $g$ -modes. The notable effect of $Δ$ resonances on neutron stars' $g$ -mode frequencies holds important implications for probing the internal composition of neutron stars.
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2606.24343 [pdf]
1 citation
10
[Submitted on 23 Jun 2026] (cross-list from hep-ph)
The $a_{1} (1420)$ in a Unitary Coupled-Channel Three-Body Approach
Ajay S. Sakthivasan🇩🇪 · Yuchuan Feng🇺🇸 · Michael Döring🇺🇸 · Maxim Mai🇺🇸
An enhancement in the three-pion energy at around $s \approx 1.42 GeV$ with $a_{1}$ quantum numbers was observed at the COMPASS experiment. This was later attributed to the triangle singularity mechanism involving an on-shell $K^{*} (892)$ , $K$ and $K ˉ$ intermediate states. The alignment of the decay $K$ with the spectator $K ˉ$ produces an $f_{0} (980)$ , resulting in a kinematic enhancement, which is classically explained by the Landau equations. However, this one-loop process forms only part of a non-diagonal transition in a much larger coupled-channel framework. This study demonstrates the feasibility of embedding one-loop triangle-singularity calculations into a unitary three-body amplitude allowing one to consistently incorporate final-state interactions and their potentially substantial effect. For this, up to $P$ -wave isobars and all sub-channel isospins are combined in a nine-channel production amplitude that is fitted to COMPASS lineshapes at different momentum transfers. The fitted amplitude reproduces the narrow enhancement in the $(π f_{0})_{P}$ channel near $s \approx 1.42$ GeV. This implies that the triangle singularity mechanism sufficiently explains the observed enhancement, and an additional genuine $a_{1} (1420)$ pole is not required. Incidentally, the parameters of the ground state axial vector resonance (the $a_{1} (1260)$ ) are also extracted from that data.
Comments:
25 pages, 11 figures, 3 tables, major revision
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2606.24709 [pdf]
0 citations
11
[Submitted on 23 Jun 2026] (cross-list from hep-ph)
Radiative decays of dynamically generated pentaquarks in the chiral unitary approach: the $P_{c} (4457) \to P_{c} (4312) γ$ transition
Ratirat Suntharawirat🇹🇭 · Nongnaphat Ponkhuha🇹🇭 · Daris Samart🇹🇭
We study the radiative decay of dynamically generated pentaquarks and apply the formalism to the transition $P_{c} (4457) (3/ 2^{-}) \to P_{c} (4312) (1/ 2^{-}) γ$ . Both states are treated as $S$ -wave hadronic molecules generated in the chiral unitary approach with heavy-quark spin symmetry and the local hidden gauge interaction. The photon therefore couples to the meson-baryon components of the two poles. The calculation combines the strong coupling residues of the coupled-channel solution, heavy-quark spin symmetry for the electromagnetic vertices, and a transverse assembly of the $M 1$ triangle loops. A complete calculation gives nineteen triangle loops. We reduce each loop to a single numerical quadrature and give the closed analytic form. The electromagnetic vertices that are not fixed by data are estimated with the naive-quark model and heavy-quark spin symmetry. We normalize the main $D^{*} D γ$ coupling to $D ˉ^{* 0} \to D ˉ^{0} γ$ and test the same convention with $J / ψ \to η_{c} γ$ . The central width is $6.7 \keV$ , with a conservative range of about $2$ to $9 \keV$ . This radiative decay process is a pure $M 1$ transition with photon energy $143 \MeV$ . The $D ˉ^{* 0} \to D ˉ^{0} γ$ loop gives the leading contribution. The near-threshold $D ˉ^{*} Λ_{c}$ loop gives the main correction. A soft Gaussian form-factor on the leading diagram reduces the width to about $2 \keV$ , compatible with earlier molecular results, and decreases the full width to about $4 \keV$ . The coherent result is sensitive to the relative residue phases in the coupled-channel convention. We also estimate the cascade rate for $Λ_{b}^{0} \to J / ψ p K^{-} γ$ and discuss how the line can be searched for. The pure $M 1$ content, the ratio to the $P_{c} (4440)$ radiative decay, and the binding-energy dependence of the width are proposed as tests of the molecular nature.
Comments:
21 pages, 3 figures, 11 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2606.24764 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE