Nuclear Theory·nucl-th

Friday·August 1, 2025

14 papers—9 primary·5 cross-listed

01
Effectiveness of parton cascade in solving the relativistic Boltzmann equation in a box
Todd Mendenhall🇺🇸 · Zi-Wei Lin🇺🇸
We benchmark the ZPC parton cascade with an exact analytical solution of the relativistic Boltzmann equation for a homogeneous and massless gas with a constant and isotropic elastic cross section. We measure the accuracy of ZPC with the relative mean deviation between its momentum distribution and the exact solution. We use two generalized collision schemes to further improve the accuracy of ZPC over the recent $t$ -minimum collision scheme. We find that ZPC can reproduce very well the time evolution of the single-particle distribution function for the exact solution's initial condition, with one generalized collision scheme giving an accuracy better than $1%$ for the momentum distribution at any time in all studied cases, including very high opacities where naively the parton cascade approach is expected to fail.
nucl-thhep-phNPB(2026)·2 citations
02
Role of $Σ^{*} (1385)$ on $Λ$ hyperon polarization in relativistic heavy ion collisions
Haesom Sung🇹🇼 · Che Ming Ko🇺🇸 · Su Houng Lee🇰🇷
The effect of $Σ^{*} (1385)$ baryon resonance on the time evolution of the $Λ$ hyperon polarization in hadronic matter is studied using a kinetic approach. This approach explicitly includes the production of the $Σ^{*}$ resonance from the $Λ - π$ and $Σ (1192) - π$ scatterings as well as its decay into $Λ + π$ or $Σ + π$ . The resulting coupled kinetic equations governing the time evolution of $Λ$ , $Σ$ and $Σ^{*}$ numbers and polarizations are solved for Au-Au collisions at $s_{N N} = 7.7$ GeV and 20-50\% centrality, using initial values determined by thermal yields and the thermal vorticity at chemical freeze-out temperature. As the hadronic matter expands and cools, the $Λ$ polarization is found to increase slightly during early times and then decreases very slowly afterwards, while the $Σ$ polarization remains nearly constant and the $Σ^{*}$ polarization continuously decreases. Including feed-down contributions to the $Λ$ polarization from the decays of partially polarized $Σ^{0}$ , $Σ^{*}$ , and $Ξ (1322)$ hyperons, where the $Ξ$ polarization is obtained by solving coupled kinetic equations for the $Ξ$ and $Ξ^{*} (1532)$ system, the resulting $Λ$ polarization becomes smaller and decreases over time. In both cases, however, the time variation of the $Λ$ polarization is sufficiently small to support the assumption of an early freeze-out of $Λ$ spin degree of freedom in relativistic heavy ion collisions.
nucl-thPRC(2026)·2 citations
03
Uncovering the nature of low-lying dipole states with QRPA calculations: is Z=42 the answer?
Eun Jin In · Emanuel Chimanski · Jutta Escher · Sophie Péru · Aaina Thapa · Walid Younes
The pygmy dipole resonance (PDR), marked by enhanced electric dipole strength near particle emission energies, offers a unique perspective on the collective dynamics of nuclear structure. Its precise nature, particularly its degree of collectivity, remains a topic of debate. In this study, we investigate low-energy dipole excitations in spherical Mo isotopes ( $^{82}$ Mo to $^{98}$ Mo) using a fully consistent Hartree-Fock-Bogoliubov (HFB) and quasiparticle random phase approximation (QRPA) framework. We observe that an enhancement in dipole strength near particle emission energies is closely correlated with the development of either neutron or proton skins. To further understand the nature of this enhancement, we examine the behavior of proton and neutron transition densities. Our analysis shows that these (low-lying dipole) states exhibit distinct characteristics involving in-phase oscillations within the nucleus and neutron- or proton-dominated oscillations at the surface, while the primary contributor to this enhancement displays an intricate underlying structure. We also investigate the collectivity of these excitations by analyzing two-quasiparticle fragmentations and relative energy shifts. Our findings reveal that skin oscillation states exhibit moderate collectivity, as indicated by substantial configuration mixing, but limited coherence, whereas the GDR states exhibit strong coherence and large energy shifts characteristic of fully developed collective motion. This study paves the way for future investigations into the collective nature of low-energy dipole states in the enhancement region, particularly in deformed nuclei, where nuclear shape effects may play a crucial role in their excitation dynamics.
nucl-th1 citation
04
Mapped $s p df$ interacting boson model for quadrupole-octupole collective states in nuclei
K. Nomura
Dipole bosons are introduced in the interacting boson model (IBM) by means of the self-consistent mean-field method. The constrained mean-field calculations employing a given nuclear energy density functional yield the potential energy surfaces in terms of the axially-symmetric quadrupole-octupole, dipole-quadrupole, and dipole-octupole deformations. By mapping these energy surfaces onto the expectation values of the IBM Hamiltonian in the coherent state of the interacting $s$ , $p$ , $d$ , and $f$ bosons, strength parameters of the $s p df$ -IBM Hamiltonian are determined. In an illustrative application to octupole-deformed actinides $^{218 - 230}$ Ra and $^{220 - 232}$ Th, it is shown that effects of including $p$ bosons in the IBM mapping are to lower significantly negative-parity yrast levels, and to improve descriptions of observed energy-level systematic in nearly spherical and transitional nuclei, and of the behaviors of the reduced electric dipole transitions and intrinsic dipole moments with neutron number.
nucl-thnucl-exPRC(2025)·2 citations
05
In-medium effects of nucleon-nucleon cross sections in heavy-ion collisions
Shuochong Han🇨🇳 · Xinle Shang🇨🇳 · Wei Zuo🇨🇳 · Gaochan Yong🇨🇳 · Ang Li🇨🇳
Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model, we systematically investigate the in-medium effects of nucleon-nucleon ( $N N$ ) cross sections on nucleonic and pionic observables in heavy-ion collisions, employing microscopic cross sections derived from the Brueckner-Hartree-Fock approach. Key observables include nuclear stopping, the neutron-to-proton ( $n / p$ ) ratio, neutron-proton transverse flow differences, differential collective flow, pion multiplicities, and the resulting $(π^{-} / π^{+})_{like}$ ratio. The analysis disentangles the respective contributions from the scattering amplitude, the density of states, and the total momentum ( $K$ ) of the colliding pairs. We find that larger in-medium $N N$ cross sections generally enhance free nucleon emission and nuclear stopping, with the nucleon effective mass playing a dominant suppressive role. However, it is insufficient to account only for the medium corrections from effective mass: both the medium effect from the scattering amplitude and the $K$ -dependence exert noticeable influences on the observables. In particular, nuclear stopping is found to be highly sensitive to these in-medium modifications of cross sections. While the $n / p$ ratio and transverse flow difference remain largely insensitive, the differential collective flow and pion yields are strongly affected. These results indicate that the interplay between scattering amplitude, density-of-states and $K$ -dependence is essential to accurately describe medium effects in heavy-ion collisions.
nucl-thPRC(2026)·2 citations
06
Neural Posterior Estimation of Neutron Star Equations of State
Valéria Carvalho · Márcio Ferreira · Michał Bejger · Constança Providência
We present a simulation-based inference (SBI) framework to constrain the neutron star (NS) equation of state (EoS) from astrophysical observations of masses, radii and tidal deformabilities, using Neural posterior estimation (NPE) with Conditional Normalising Flows (CNF). To ensure that the model conforms with reality, physics-informed constraints are embedded directly into the training loss. This enables efficient, likelihood-free inference of full posterior distributions for key thermodynamic quantities-including pressure, squared speed of sound, and the trace anomaly-conditioned on observational data. Our models are trained on synthetic datasets generated from two agnostic EoS priors: polytropic parametrizations (PT) and gaussian process (GP) reconstructions. These datasets span various scenarios, including the presence or absence of tidal deformability information and observational noise. Across all settings, the method produces accurate and well-calibrated posteriors, with uncertainties reduced when tidal deformability constraints are included. Furthermore, we find that the behavior of normalized predictive dispersions is strongly correlated with the maximum central density inside NSs, suggesting that the model can indirectly infer this physically meaningful quantity. The approach generalizes well across EoS families and accurately reconstructs derivative quantities such as the polytropic index, demonstrating its robustness and potential for probing dense matter in NS cores.
nucl-thastro-ph.HEhep-phPRD(2025)·5 citations
07
Nuclear Matter and Finite Nuclei: Relativistic Thomas-Fermi Approximation Versus Relativistic Mean-Field Approach
Shuying Li · Hong Shen · Jinniu Hu
The Thomas-Fermi approximation is a powerful method that has been widely used to describe atomic structures, finite nuclei, and nonuniform matter in supernovae and neutron-star crusts. Nonuniform nuclear matter at subnuclear density is assumed to be composed of a lattice of heavy nuclei surrounded by dripped nucleons, and the Wigner-Seitz cell is commonly introduced to simplify the calculations. The self-consistent Thomas--Fermi approximation can be employed to study both a nucleus surrounded by nucleon gas in the Wigner-Seitz cell and an isolated nucleus in the nuclide chart. A detailed comparison is made between the self-consistent Thomas-Fermi approximation and the relativistic mean-field approach for the description of finite nuclei, based on the same nuclear interaction. These results are then examined using experimental data from the corresponding nuclei.
nucl-thUniverse(2025)·1 citation
08
Fast prediction of the hydrodynamic QGP evolution in ultra-relativistic heavy-ion collisions using Fourier Neural Operators
David Stewart🇺🇸 · Joern Putschke🇺🇸
Recent research in machine learning has employed neural networks to learn mappings between function spaces on bounded domains termed ``neural operators''. As such, these operators can provide alternatives to standard numerical methods for partial differential equation (PDE) solutions. In particular, the Fourier Neural Operator (FNO) has been shown to map solutions for classical fluid flow problems with accuracy competitive with traditional PDE solvers and with much greater computing speed. This paper explores the first application of FNOs to model ultra-relativistic hydrodynamic flow of the quark-gluon plasma (QGP) generated in relativistic heavy-ion collisions. The application in ultra-relativistic flow is novel relative to classical flow, due to the hydrodynamic evolution of the QGP occurring in femtometer-scaled explosions characterized by rapid expansion cooling. In this study we investigate the applicability of FNOs as computationally fast alternatives to standard numerical PDE solvers. The FNO predictions are evaluated by comparing to standard PDE solutions, using \MUSIC in the \JETSCAPE Monte Carlo event generator framework. The performance of calculating established experimental observables for flow and jet quenching using FNOs in the MC framework are also reported.
nucl-thhep-exPRC(2026)·2 citations
09
Searching for Solitons in Heavy-Ion Reactions near the Fermi Energy
Theodoros Depastas · Aldo Bonasera · Joseph B. Natowitz
Solitons are special shape-conserving hydrodynamical solutions that appear in many areas of physics. Here, we explore the existence of such solutions in microscopic descriptions of the heavy ion reaction $^{12}$ C + $^{28}$ Si $\to$ $^{12}$ C $^{*}$ + 7 $α$ in the range E/A=10-65 MeV/u. After recognizing the centrality of the collision and time-reversibility as fundamental requirements for the presence of solitonic $^{12}$ C, we utilize the Hybrid $α$ -Cluster model for our analysis with a novel methodology. Our results suggest soliton production for E/A=25-45 MeV/u in the forward direction, with a total cross section being at least in the order of a few $μ$ b. This, apart from being encouraging for possible experimental studies, maybe connected to possible toroid states of $^{28}$ Si at low angular momenta.
nucl-thPLB(2025)·3 citations
10
Heavy flavored hydrogen molecule systems
Hui-Min Yang · Yao Ma · Shi-Lin Zhu
This study provides a comprehensive analysis of $S$ -wave exotic hydrogen-like three-body systems ( $pp μ^{-}$ , $pp τ^{-}$ , $μ^{-} μ^{-} p$ , $τ^{-} τ^{-} p$ , $p μ^{-} τ^{-}$ ) with spin-parity $J^{P} = 1/ 2^{+}$ and $3/ 2^{+}$ , and four-body systems ( $pp μ^{-} μ^{-}$ , $pp τ^{-} τ^{-}$ ) with $J^{P} = 0^{+}$ , $1^{+}$ , and $2^{+}$ . We use complex scaling and Gaussian expansion methods to solve the complex-scaled Schrödinger equation and obtain possible bound and quasi-bound states. The resulting binding energies range from $- 33.8$ ~keV to $- 340$ ~eV. Notably, we present the first theoretical estimation of the bound-state energy levels of $pp μ^{-} μ^{-}$ and $pp τ^{-} τ^{-}$ , which is of significant importance for understanding exotic few-body Coulomb systems. We further analyze spin configurations and root-mean-square radii to elucidate the spatial structure of these bound and quasi-bound states. Our results reveal that $K$ -type spatial configurations play a crucial role in accurately describing bound and quasi-bound states in the hydrogen-molecule-like systems $pp μ^{-} μ^{-}$ and $pp τ^{-} τ^{-}$ . Incorporating $K$ -type configurations significantly alters the mass spectra of these states. Future muon colliders and muon facilities may offer promising platforms for the possible copious production of such heavy flavored hydrogen molecules and molecular ions. For instance, scattering processes such as $2 μ^{-} + H_{2} \to H_{2 μ} + 2 e^{-}$ , $μ^{-} + H_{2} \to H_{μ e} + e^{-}$ , and $μ^{-} + H_{2}^{+} \to H_{2 μ}^{+} + e^{-}$ could be utilized, facilitating detailed studies of intriguing states such as $H_{2 μ}$ , $H_{μ e}$ , and $H_{2 μ}^{+}$ .
↳ physics.atom-phhep-exhep-phnucl-thPRA(2025)·2 citations
11
Local spin polarization by color-field correlators and momentum anisotropy
Haesom Sung🇹🇼 · Berndt Müller🇺🇸 · Di-Lun Yang🇹🇼
We study the local spin polarization of quarks induced by color-field correlators stemming from the correlation of chromo-Lorentz force and chromo-magnetic polarization or chromo-spin Hall effect in the presence of momentum anisotropy. Such effects can trigger longitudinal polarization from fluctuating color fields in glasma or quark gluon plasma phases with transverse expansion for relativistic heavy ion collisions. Especially, from the glasma effect, the resulting longitudinal polarization spectrum of $Λ/ Λ ˉ$ hyperons has a sinusoidal structure with twice the azimuthal angle relative to the anisotropic direction. An order-of-magnitude estimate of the effect aligns with experimental observations. Our findings highlight the significant role of coherent gluon fields as a novel source for spin polarization phenomena in high-energy nuclear collisions.
↳ hep-phhep-thnucl-thJ.Subatomic Part.Cosmol.(2026)·1 citation
12
Electric, thermal and thermoelectric response of a hot pion gas in a time dependent background magnetic field
Ankit Kumar🇮🇳 · Gowthama K K🇮🇳 · Vinod Chandra🇮🇳 · Sadhana Dash🇮🇳
The prime focus of the work is to determine the electric, thermal and thermoelectric transport coefficients of a hot pion gas in the presence of time-dependent background magnetic fields. The thermoelectric effect is analyzed by examining the magneto-Seebeck and Nernst coefficients in the hot pionic medium under such conditions. Furthermore, the phenomenologically relevant elliptic flow coefficient, linked to the Knudsen number, is examined. The analysis reveals the significant impact of both the strength and time dependence of the magnetic field on the transport coefficients of the pionic medium. The results are analyzed in contrast to those obtained under a constant magnetic field.
↳ hep-phnucl-thPRD(2025)·3 citations
13
Poincaré covariant quantum molecular dynamics: a covariant description of a system of interacting wave packets
Yasushi Nara🇯🇵 · Asanosuke Jinno🇯🇵 · Koichi Murase🇯🇵
We present a new formulation for the mean-field propagation part of the relativistic quantum molecular dynamics, simulating an $N$ -body system of interacting Gaussian wave packets via Lorentz scalar and vector potentials. Covariant equations of motion are derived based on the principle of least action. These covariant equations of motion can be solved with a computational cost comparable to that of conventional noncovariant quantum molecular dynamics. Furthermore, the new equations of motion accurately estimate the density-dependent potential, as demonstrated through comparison of the forces with the numerical integration. We apply them to $N$ -body systems interacting via the Skyrme-type potentials or the relativistic mean field to simulate heavy-ion collisions. Our results show that the derived equations of motion provide a robust approximation to the dynamics of the full numerical integrations.
↳ hep-phnucl-exnucl-th2 citations
14
Scale-anomaly-induced binding pressure in hadrons
Daisuke Fujii🇯🇵 · Mitsuru Tanaka🇯🇵
The effect of the QCD scale anomaly on the internal pressure distribution of hadrons is studied based on the trace-traceless decomposition of the energy-momentum tensor. Using recent model-independent results of gravitational form factors as input, the pressure distributions of both pions and nucleons are analyzed in the instant form and the light-front form. It is found that, in all cases, the scale anomaly dominantly generates the negative binding pressure. This result suggests that the phenomenon is a universal feature, independent of models, types of hadrons, and the choice of form.
↳ hep-phhep-exhep-lathep-th+1PLB(2025)·10 citations

Affiliations

first authorsco-authorsvia INSPIRE