Nuclear Theory·nucl-th

Wednesday·April 8, 2026

14 papers—7 primary·7 cross-listed

01
Species-dependent viscous corrections at particlization: A novel relaxation time approximation approach
I. Aguiar🇧🇷 · T. Nunes da Silva🇧🇷 · G. S. Denicol🇧🇷 · M. Luzum🇧🇷 · G. S. Rocha🇧🇷 · C. Shen🇺🇸
We assess the effects of a recently proposed generalized relaxation time approximation (RTA) for multi-species relativistic gases within a realistic numerical hybrid framework and study its phenomenological consequences in p-Pb and Pb-Pb collisions. The novel approximation introduces counter-terms to the collision kernel, allowing for momentum-dependent relaxation times $τ_{i} (p)$ while preserving local energy-momentum conservation. As a consequence, the resulting first-order viscous corrections $δ f_{i}$ to the phase-space distribution functions depend explicitly on the particle species mass $m_{i}$ . We systematically investigate the impact of these species-dependent corrections on particle production at particlization, focusing on identified hadron yields and transverse momentum ( $p_{T}$ ) spectra obtained from Cooper-Frye sampling. We find that the yields and spectra of light hadrons ( $π, K, p$ ) are significantly affected, leading to modifications of relative particle yields such as the $K / π$ and $p / π$ ratios. We show that these effects persist, albeit with reduced magnitude, after the inclusion of the hadronic cascade stage. In contrast, the impact on inclusive charged-particle observables is strongly reduced due to compensating enhancements and suppressions among different species. This controlled deformation of identified hadron observables, which selectively modifies flavor-sensitive quantities, makes the new prescription particularly well suited for Bayesian inference, as it introduces new sensitivity directions without spoiling existing constraints. Overall, our results demonstrate that species-dependent viscous corrections arising from the generalized RTA can leave significant and observable imprints on identified hadron production and relative yields, while remaining fully consistent with the successful description of bulk collective flow observables.
nucl-thhep-ph0 citations
02
Equilibrated fraction of QCD matter in high-energy oxygen--oxygen collisions
Naoya Ito🇯🇵 · Tetsufumi Hirano🇯🇵
We quantify to what degree the QCD matter created in high-energy oxygen--oxygen ( $O + O$ ) collisions at $s_{N N} = 5.36$ TeV reaches a locally equilibrated state. For this purpose, we employ a novel framework based on the core--corona picture that describes the dynamics of both locally equilibrated fluids (the core) and nonequilibrium particles (the corona). Contributions from the core become larger than those from the corona above charged-particle multiplicity at midrapidity, $⟨ d N_{ch} / d η ⟩_{∣ η ∣ < 0.5} \approx 20$ . We also find that nonnegligible contributions from the corona still remain even in central $O + O$ collisions. The yield ratios of strange baryons to charged pions exhibit an increasing behavior with increasing multiplicity at midrapidity. However, these ratios are smaller than those obtained when assuming that QCD matter has reached complete chemical equilibrium. These results demonstrate that a purely hydrodynamic approach is insufficient and that the inclusion of a corona component is essential for describing the dynamics of intermediate-size systems such as $O + O$ collisions.
nucl-thhep-phnucl-exPRC(2026)·2 citations
03
Predictions of charge density distributions for nuclei with $Z \geq 8$
Yun Dong Wang · Tian Shuai Shang · Hui Hui Xie · Peng Xiang Du · Jian Li · Haozhao Liang
A deep neural network (DNN) has been developed to accurately predict nuclear charge density distributions for nuclei with proton numbers $Z \geq 8$ . By incorporating essential nuclear structure features, the model achieves a significant improvement in predictive accuracy over conventional methods. The charge density distributions are analyzed using a Fourier-Bessel (FB) series expansion, and the DNN is trained on a comprehensive dataset derived from relativistic continuum Hartree-Bogoliubov (RCHB) theory calculations. The model demonstrates exceptional performance, with root-mean-square deviations of 0.0123 fm and 0.0198 fm for charge radii on the training and validation sets, respectively, remarkably surpassing the precision of the original RCHB calculations. Beyond advancing nuclear physics research, this high-precision model provides critical data for applications in atomic physics, nuclear astrophysics, and related fields.
nucl-thcs.LGphysics.atom-phNucl.Sci.Tech.(2026)·5 citations
04
Impact of neutron-proton pairing on the nucleon high-momentum distribution in symmetric nuclear matter
Guo-peng Li · Ji-you Fu · Jin Zhou · Xin-le Shang · Jian-min Dong · Wei Zuo
The effect of neutron-proton ( $n p$ ) pairing on the high-momentum tail (HMT) of nucleon momentum distributions in symmetric nuclear matter is investigated within a combined framework of the extended Brueckner-Hartree-Fock approach with off-shell BCS theory. The HMT ratio, quantifying the high-momentum fraction in the BCS state relative to the normal state, reaches about $1.06$ around the density of $0.052 fm^{- 3}$ , indicating that the maximal contribution of the $n p$ pairing, amounts to approximately 6\% that from short-range correlations (SRCs). This contribution exhibits a density dependence that closely follows the squared relative pairing gap $Δ_{F} = Z_{F} Δ (k_{F})$ with respect to the kinetic energy $E_{k_{F}}^{*}$ evaluated using the effective mass, suggesting that $Δ_{F}^{2} / E_{k_{F}}^{* 2}$ provides a qualitative measure of the $n p$ pairing effect on the HMT. These findings highlight the significant role of $n p$ pairing and its interplay with SRCs in shaping nucleon momentum distributions in nuclear matter.
nucl-thPRC(2026)·1 citation
05
Channel couplings redirect absorbed flux from peripheral loss to fusion in weakly bound nuclear reactions
Hao Liu · Jin Lei · Zhongzhou Ren
In reactions of weakly bound nuclei, the absorption cross section mixes two physically distinct contributions: inner capture associated with compound-nucleus formation, and peripheral losses from breakup, transfer, and other direct reactions. Within a framework that combines an ingoing-wave boundary condition (IWBC) at an inner radius with a complex potential in the external region, we derive the exact flux identity $σ_{abs} = σ_{fusion} + σ_{W}$ from the radial continuity equation. The resulting partition is exact within the adopted CC/CDCC model space and provides a practical diagnostic of where absorbed flux is removed. Applied to $^{6}$ Li+ $^{209}$ Bi, the analysis reveals that channel couplings qualitatively reorganize the absorbed flux: the dominant absorption mechanism shifts from peripheral loss at sub-barrier energies to inner capture above the barrier, whereas the single-channel baseline remains peripheral-loss dominated throughout. The resulting IWBC-defined inner-capture cross section tracks the measured complete-fusion excitation function with only a modest dependence on the chosen boundary radius. Together with the exact identity $σ_{abs} = σ_{fusion} + σ_{W}$ , this agreement supports interpreting the peripheral term $σ_{W}$ as a major spatial contributor to the well-known CF suppression in weakly bound systems.
nucl-thPLB(2026)·2 citations
06
Beam energy dependence of identified particle production in heavy-ion collisions using a parton-hadron string dynamics model
Towseef Bhat🇮🇳 · Vipul Bairathi🇨🇱 · Lokesh Kumar🇮🇳 · Sonia Kabana🇨🇱
We report predictions for the transverse momentum ( $p_{T}$ ) spectra of $π^{\pm}$ , $K^{\pm}$ , $p$ , and $p ˉ$ in various collision centrality from Au + Au collisions at beam energies ( $E_{l ab}$ ) of 6.7, 8, 11, and 25 A~GeV using a parton-hadron string dynamics (PHSD) transport model. We studied the dependence of particle yields ( $d N / d y$ ), mean transverse momenta ( $⟨ p_{T} ⟩$ ), and particle ratios on collision energy and centrality to understand the underlying mechanisms of particle production. A comparison of the PHSD model results with available experimental measurements provides a qualitative description of these observables. Our results highlight the importance of baryon stopping, strangeness production, pair production, and baryon-antibaryon annihilation in the high baryon density region. These findings also provide theoretical insights relevant to the ongoing beam energy scan program at RHIC and the future heavy-ion programs at FAIR and NICA.
nucl-thhep-exhep-phnucl-ex0 citations
07
Uncertainty quantified three-body model applied to the two-neutron halo $^{22}$ C
Patrick McGlynn🇺🇸 · Chloë Hebborn🇺🇸
Two-neutron halo nuclei offer a fascinating probe into the behaviour of quantum few-body systems at the limits of binding. Although few nuclei have already been clearly identified, many of their properties remain poorly constrained. $^{22}$ C, one of the heaviest, still lacks a precise identification of its static and dynamic properties, such as its mass and dipole strength in the continuum. One main difficulty is that properties of two-neutron halo nuclei are inferred from experimental data using a theoretical model. Therefore, accurately determining the characteristics of two-neutron halo nuclei requires an accurate theoretical model and careful quantification of the uncertainties. In this work, we examine $^{22}$ C with a three-body model, seeing $^{22}$ C as a $^{20}$ C core and two halo neutrons, and quantify for the first time the uncertainties associated with the $^{20}$ C- $n$ interaction using a Bayesian approach. We propagate these uncertainties to properties of bound and scattering states of $^{22}$ C, as well as its dipole strength. The comparison of our prediction for the matter radius to experimentally-derived values suggests that $^{22}$ C is bound by less than 0.35~MeV and is dominated by a $(s_{1/2})^{2}$ configuration. Our analysis of the dipole strength shows that final-state interaction needs to be included for an accurate description, the uncertainties on the strength function are about 50\% and are mostly influenced by uncertainties on the ground-state properties, and partial-wave occupation of $^{22}$ C depends on the scattering length and the $d_{3/2}$ resonance energy of the $^{20}$ C- $n$ unbound system. Such sensitivity of the dipole strength to the properties of both $^{21}$ C and $^{22}$ C properties motivates a precise measurement of the $^{22}$ C dipole strength function, that will allow to precisely and accurately resolve the spectroscopy of these nuclei.
nucl-thPLB(2026)·0 citations
08
Multiquark clustering in neutron-star matter from color-spin molecular dynamics
Nobutoshi Yasutake🇯🇵 · Yuta Mukobara🇮🇹 · Aaron Park🇰🇷 · Su Houng Lee🇰🇷 · Toshiki Maruyama🇯🇵
We study the equation of state of neutron-star matter with color-spin molecular dynamics. The calculation includes the internal color and spin degrees of freedom and their time evolution. The matter composition, including strangeness under $β$ equilibrium, is determined by energy minimization. We find two main trends. First, within the present color-spin molecular dynamics framework and under the adopted clustering criterion along the stable neutron-star branch, isolated quarklike configurations do not appear; instead, color-magnetic interactions favor the self-consistent formation of multiquark clusters. Within the same criterion, the cluster-size distribution is concentrated at quark numbers that are multiples of three, corresponding to integer baryon numbers. Second, relative to the conventional no- $K^{*}$ baseline, the interaction between strange and light quarks has a strong impact on neutron-star radii. This suggests that future radius measurements, together with phenomenological information on the strangeness-onset density, may help constrain flavor-sector interactions involving strangeness.
↳ astro-ph.HEnucl-thPRD(2026)·0 citations
09
Non-universality of color transparency onset in pion and kaon electroproduction
Byung-Geel Yu · Tae Keun Choi · Kook-Jin Kong
A combined analysis of the Jefferson Lab data on nuclear transparency in $A (e, e^{'} π^{+})$ and $A (e, e^{'} K^{+})$ shows that the onset of color transparency (CT) is not universal across meson flavors. The pion transparency is well reproduced by the standard quantum diffusion model (QDM) with $Δ M_{π}^{2} ≃ 0.7$ GeV $^{2}$ , whereas the kaon data favor the quadratic expansion of the naive parton model (NPM) with the natural hadronic scale $R_{K} \sim σ_{K N} / π$ . This dichotomy cannot be repaired by physically motivated parameter choices: the pion slope excludes the quadratic expansion with any physical radius, and the kaon slope requires a QDM excitation scale far below the range conventionally used in pion transparency analyses. A microscopic interpretation, in which the diffusive evolution of the pion appears as an exceptional consequence of its Goldstone-boson nature while the kaon follows the generic ballistic expansion, is discussed.
↳ hep-phnucl-th0 citations
10
Probing the chiral magnetic effect via transverse spherocity event classification in relativistic heavy-ion collisions
Somdeep Dey🇮🇳 · Abhisek Saha🇨🇳
We present the first study of the Chiral Magnetic Effect (CME) using transverse spherocity as an event-shape classifier in Pb+Pb collisions at $s_{N N} = 5.02$ TeV, simulated with the A Multi-Phase Transport (AMPT) model with a realistic CME implementation. Transverse spherocity separates events into jetty and isotropic topologies based on the geometric distribution of transverse momentum. Unlike traditional event shape engineering methods, which use the flow vector as an event classifier that is itself contaminated by the very backgrounds it is intended to suppress, spherocity provides a cleaner, geometry-driven classification that avoids this circular limitation. CME inclusion shifts the spherocity distribution toward more isotropic events, confirming its sensitivity to CME-induced charge separation. The charge-dependent azimuthal correlator $Δ γ$ and correlated background coupled with elliptic flow are consistently higher in jetty events. The scaled ratio $Δ γ / v_{2}$ shows enhanced values for isotropic events, confirming effective background suppression after elliptic flow scaling. Our results demonstrate that isotropic event selection via transverse spherocity provides a cleaner and more reliable environment for CME searches by simultaneously suppressing flow-driven and resonance-decay backgrounds, making it a powerful complementary method to existing flow-vector-based methods.
↳ nucl-exhep-phnucl-th0 citations
11
Observation of nuclear suppression in coherent $Υ$ (1S) photoproduction off heavy nuclei at the LHC
CMS Collaboration
The first measurement of coherent $Υ$ (1S) meson photoproduction off heavy nuclei is performed using ultraperipheral lead-lead collisions collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The nuclear gluonic structure is probed at a nucleon momentum fraction of order $x$ $\sim$ 10 $^{- 3}$ , determined by the kinematics of the process. Owing to the large $Υ$ (1S) mass, the measurement reaches the highest scale accessible so far through coherent vector-meson photoproduction, $μ^{2}$ = 22.4 GeV $^{2}$ , where nonlinear quantum chromodynamics effects are expected to be minimal. In the $Υ$ (1S) rapidity range $∣ y ∣$ $<$ 1, the ratio of the measured photoproduction cross section to a baseline model prediction that neglects nuclear effects is $S_{Υ (1S)}$ = 0.25 $\pm$ 0.06 (stat) $\pm$ 0.02 (syst), thereby demonstrating nuclear suppression in this process. Expressed in terms of a nuclear gluon suppression factor, the result yields $R_{g}^{Pb}$ ( $x$ $\approx$ 10 $^{- 3}$ , $μ^{2}$ = 22.4 GeV $^{2}$ ) = 0.55 $\pm$ 0.12 (stat) $\pm$ 0.02 (syst). The measured $R_{g}^{Pb}$ is only slightly larger than the values previously reported for coherent $ϕ$ photoproduction, despite the probed $μ^{2}$ differing by approximately two orders of magnitude.
↳ nucl-exhep-exnucl-th4 citations
12
Thermodynamic and Transport Properties of Quark-Gluon Plasma at Finite Chemical Potential with a DNN framework
Rishabh Kumar Tiwari🇮🇳 · Kangkan Goswami🇮🇳 · Suraj Prasad🇮🇳 · Captain R. Singh🇮🇳 · Raghunath Sahoo🇮🇳 · Mohammad Yousuf Jamal🇨🇳
The characteristics of a thermal system depend strongly on its response to thermal gradients and the underlying microscopic interactions among constituents. In the present study, we investigate the thermodynamic and transport properties of the quark-gluon plasma (QGP) at finite baryon chemical potential within a deep-learning-assisted quasi-particle model (DLQPM). The temperature ( $T$ ) and baryon chemical potential ( $μ_{B}$ )-dependent thermal masses of quasi-particles are estimated using neural networks trained to reproduce lattice QCD (lQCD) results for the equation of state, obtained via a Taylor-like expansion around vanishing baryon chemical potential. The trained model acts as an effective emulator, enabling us to estimate the thermodynamic and transport properties at finite $μ_{B}$ . We compute the speed of sound, specific heat, viscosity, and conductivity of the deconfined medium. Our findings are in good agreement with available lattice calculations and other phenomenological models. The present study demonstrates that a DNN-based approach provides an efficient framework for studying the properties of the QGP at finite baryon density.
↳ hep-phhep-exhep-latnucl-ex+12 citations
13
$N = 4$ supersymmetric Yang-Mills thermodynamics to order $λ^{5/2}$
Margaret E. Carrington🇨🇦 · Gabor Kunstatter🇨🇦 · Ubaid Tantary🇸🇦
We calculate the resummed perturbative free energy of $N = 4$ supersymmetric Yang-Mills in four spacetime dimensions (SYM $_{44}$ ) to order $λ^{5/2}$ in the 't Hooft coupling at finite temperature and zero chemical potential. All infrared divergences cancel when we include contributions from SYM $_{44}$ ring diagrams and the final result is both ultraviolet and infrared finite. Our result has special significance since order $λ^{5/2}$ is the highest order calculation that can be done with perturbation theory, because there are nonperturbative effects associated with the magnetic mass scale that come into play at order $λ^{3}$ . We compare results obtained with regularization by dimensional reduction (RDR), which preserves supersymmetry, and canonical dimensional regularization (DR). We also compare with a generalized Padé approximant constructed by matching the weak coupling result at order $λ^{2}$ and the large $N_{c}$ strong coupling result at order $λ^{- 3/2}$ . Finally we make a comparison between our result and the QCD free energy and show that SYM $_{44}$ has better convergence properties.
↳ hep-thhep-phnucl-thPRD(2026)·2 citations
14
Reference Energies for Non-Relativistic Core Ionization Potentials
Antoine Marie · Loris Burth · Pierre-François Loos
Deep-lying core electrons carry highly localized, site-specific information that forms the basis of X-ray photoelectron spectroscopy. Accurately predicting their associated core ionization potentials (IPs) is a demanding theoretical task, requiring a balanced treatment of strong orbital relaxation, electron correlation, and relativistic effects. Over the years, a variety of approaches have been developed, ranging from state-specific wave function methods to linear-response formalisms and Green's function techniques. However, their assessment has often relied on comparisons with experiment, where multiple sources of error (basis set incompleteness, relativistic corrections, and vibrational effects) are entangled, making it difficult to isolate the performance of correlation treatments. In the present work, we establish a consistent, theory-based benchmark for core IPs by computing 84 non-relativistic values (73 second-row and 11 third-row IPs) at the full configuration interaction level within the core-valence separation approximation, using large correlation-consistent basis sets augmented with tight-core and diffuse functions (aug-cc-pCVXZ). These results define theoretical best estimates within a fixed finite basis set, providing a chemically accurate reference for method development and validation. Importantly, our dataset allows for systematic, theory-versus-theory comparisons that disentangle correlation and relaxation effects from other physical contributions. On this basis, we assess the performance of widely used approximate methods, including equation-of-motion coupled-cluster approaches up to the inclusion of quadruple excitations, the one-shot $G_{0} W_{0}$ scheme, as well as state-specific methods.
↳ physics.chem-phcond-mat.mtrl-scinucl-thJ.Chem.Theor.Comput.(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE