Nuclear Theory·nucl-th

Thursday·July 9, 2026

14 papers—4 primary·10 cross-listed

01
Kaon-deuteron correlation function from an effective field theory approach
Juan Torres-Rincon · Àngels Ramos
We present a study of femtoscopic correlation functions for $K^{-} d$ and $K^{+} d$ pairs, and compare our results with recent measurements by the ALICE Collaboration in both Pb-Pb and high-multiplicity $pp$ collisions. The kaon-deuteron wave functions are derived from scattering amplitudes using a unitarized chiral effective theory model describing the elementary interactions of $K^{\pm}$ mesons with nucleons. We then evaluate the $K^{\pm} d$ strong scattering amplitudes by solving the Faddeev equations within two distinct frameworks: the Impulse Approximation and the Fixed Center Approximation, which accounts for multiple scatterings. We also incorporate the long-range Coulomb effects between the kaon and the deuteron. We show that the $K^{-} d$ correlation function exhibits large sensitivity to both the size of the emitting source and the relative momentum of the pair, being heavily influenced by rescattering processes. In contrast, the $K^{+} d$ correlation function is dominated by the weakly repulsive $K^{+} N$ interaction, showing deviations from purely Coulombic behavior only at small emission source sizes. Our predictions are in agreement with the ALICE experimental data, and also with the energy-shift and width of the $1 s$ level of the kaonic deuterium preliminary results from the SIDDHARTA 2 Collaboration.
nucl-thhep-phActa Phys.Polon.Supp.(2026)·0 citations
02
Machine learning the impact parameter in heavy-ion collisions at $s_{NN}$ = 4 and 11 GeV: a cross-check study with UrQMD, AMPT, and JAM
Xiaoqing Yue🇨🇳 · Guojun Wei🇨🇳 · Yongjia Wang🇨🇳 · Zhilong Li🇨🇳 · Pengcheng Li🇨🇳 · Haojie Xu🇨🇳 · Xiangrong Zhu🇨🇳 · Qingfeng Li🇨🇳 · Fuhu Liu🇨🇳 · Yasushi Nara🇨🇳
By generating heavy-ion collision data with the ultrarelativistic quantum molecular dynamics (UrQMD) model, a multiphase transport (AMPT) model, and the JAM model, the impact parameter ( $b$ ) in Au+Au collisions at $s_{NN}$ = 4 and 11 GeV is reconstructed using supervised learning and unsupervised learning in machine learning (ML). In supervised learning, the performance of ML algorithm is cross-checked by using data obtained from these three transport models. It is found that the typical mean absolute error (MAE) which measures the average magnitude of the absolute difference between the true and predicted $b$ is between 0.2-0.4 fm, even when training ML algorithm with data generated from one model but testing with data from others. While the conventional method (i.e., a polynomial fit to multiplicity as a function of $b$ ) only works for data generated from the same model. In the classification task, the present ML-based method also shows significantly superior results compared to the traditional approach. In unsupervised learning, the K-means clustering algorithm is used to partition collision events directly from experimental-style observables, showing that the algorithm autonomously identifies six clusters corresponding to different centrality classes without relying on predefined model-based binning. Our study demonstrates the strong robustness of using an ML algorithm trained on transport-model data for impact-parameter determination, and indicates that this method has the potential to be generalized to handle real experimental data.
nucl-thPRC(2026)·1 citation
03
Hadronic and partonic composition of QCD matter across the crossover
Artemiy Lysenko🇺🇦 · Mark I. Gorenstein🇺🇦 · Marek Gazdzicki🇵🇱 · Roman Poberezhniuk🇺🇦 · Volodymyr Vovchenko🇺🇸
We construct a simple equation of state of strongly interacting matter at zero chemical potentials that provides a unified description of lattice QCD thermodynamics in terms of hadronic and partonic degrees of freedom. The hadronic phase is described by the quantum van der Waals hadron resonance gas, extended by excluded-volume repulsion between mesons, while the quark-gluon plasma is modeled as an ideal gas of quarks and gluons supplemented with a phenomenological interaction term proportional to $T^{3}$ . The two regimes are connected by a smooth crossover switching function. The three model parameters - the meson hard-core radius, the strength of the partonic interaction term, and the switching temperature - are determined from a fit to lattice QCD results for the trace anomaly. The resulting equation of state reproduces the lattice data on the pressure, entropy density, energy density, and speed of sound in the temperature range $T = 100$ - $500$ MeV. The fit yields a meson hard-core radius $r_{M} ≃ 0.2$ fm, a partonic interaction scale $A ≃ 600$ MeV, and a switching temperature $T_{0} ≃ 216$ MeV, substantially exceeding both the pseudocritical temperature of the QCD chiral crossover and the chemical freeze-out temperature. This finding suggests that the transition from hadronic to partonic degrees of freedom is considerably more gradual than indicated by the chiral pseudocritical temperature alone, with hadronic states remaining an important component of strongly interacting matter up to temperatures of about $250$ MeV, well above the QCD chiral crossover.
nucl-thhep-ph0 citations
04
Extracting Barrier Distributions from Fusion Cross Sections
Aaron Philip
Studying fusion cross sections provides insight into the fusion process, details about the internal structure of heavier nuclear systems, and a window into astrophysical processes. Barrier distributions, extracted from fusion excitation functions, are immensely useful for comparing theoretical model predictions and experimental results. Extracting this barrier distribution from the measured cross-section data amounts to taking the second derivative of the energy-weighted cross section. In practice, barrier distributions are highly sensitive to the quality of collected experimental data and the choice of step size when using standard point difference schemes. In this work, we explore Bayesian methods for extracting a posterior distribution over barrier distributions that could reasonably describe experimental data. We benchmark Gaussian processes and recently developed Bayesian machine learning inference algorithms against realistic simulated data generated from a simple model of fusion excitation functions. We find that Gaussian processes often exhibit aliasing at higher energies of the barrier distribution. We demonstrate that the BNN architectures can more faithfully recover the barrier distribution with quantified uncertainties at all energies, while also identifying key regions of high uncertainty and model discrepancy to determine precisely where additional experiments would be maximally impactful. We use our conclusions to calibrate models to measured experimental data. All methods are comparatively robust to data sparsity and irregularity, but we find that the single most important factor dictating the fidelity of all models is the relative size of experimental uncertainties. We release an open-source version of our analysis and a user-friendly implementation of our method to encourage its future usage for experimental analysis.
nucl-th1 citation
05
Three-flavor supernova neutrino simulation using a hybrid quantum-classical algorithm with qutrits
Daniel J. Heimsoth🇺🇸 · A. Baha Balantekin🇺🇸 · Pooja Siwach🇺🇸
We simulate a self-interacting three-flavor neutrino system within a core-collapse supernova using a hybrid classical-quantum algorithm on a qutrit computer. Based on the Dirac-Frenkel evolution equations, we employ a variation of the quantum-assisted simulator to calculate the system's time evolution operator by performing qutrit Hadamard tests to find expectation values of unitary operators in the Hamiltonian. The time evolution simulation is then done classically. We find that the hybrid algorithm produces results comparable to an exact numerical integration out to times of $t \approx 30 ω_{0}^{- 1}$ with time step $δ t = 0.005 ω_{0}^{- 1}$ , where $ω_{0}$ is the energy scale of the single neutrino vacuum oscillations. We discuss the lessons learned in simulating neutrino systems using this hybrid quantum-classical algorithm, along with the advantages it offers over quantum Trotterization.
↳ hep-phastro-ph.HEastro-ph.SRnucl-th+1PRD(2026)·3 citations
06
Anomaly Realization in Charge-Flux Detector Correlators
João Barata🇨🇭 · Ratmir Jumanov🇷🇺 · Andrey V. Sadofyev🇪🇸
Quantum anomalies provide a bridge between ultraviolet properties of a theory and its infrared sector. We study how this connection appears in axial-charge-flow observables. In the simplest example, an axial-charge detector probes the fermionic cut of the anomalous triangle and resolves its infrared content as an angular distribution. The massless limit does not commute with the angular integration: a contribution suppressed at fixed angle collapses onto the two beam-collinear directions while retaining the finite integrated sum rule fixed by the axial anomaly. We then replace the axial-charge detector by higher-spin helicity (zilch) detectors and study a family of axial-anomaly-controlled energy-weighted sum rules for the corresponding fluxes. We further show that the same singular localization mechanism and finite zilch-flux sum rules persist in the mixed axial-gravitational channel. We briefly comment on extensions to more general states and multipoint correlators.
↳ hep-phhep-thnucl-th3 citations
07
The Generalization Gap in Machine Learning EoS Inference from Core-Collapse Supernova Gravitational Waves
Ayan Mitra
Core-collapse supernova gravitational waves may carry information about the dense matter equation of state (EoS), which describes the relation between pressure, density, temperature, and composition. This work tests a crucial question for physical inference: can a machine learning model trained on a finite simulation catalogue predict EoS parameters for an EoS family that was absent during training? Under standard random cross-validation, a LightGBM regressor appears highly successful, yielding $R^{2} = (0.70, 0.67, 0.60)$ for the nuclear incompressibility, symmetry energy, and slope parameter $(K_{0}, J, L)$ . However, under Leave-One-EoS-Out (LOEO) validation, where all waveforms from a single EoS are withheld, the model fails, yielding mean absolute errors of $(44.57, 3.19, 30.54)$ MeV and negative pooled $R^{2}$ scores, performing worse than a baseline mean predictor. This generalisation gap persists across linear models, random forests, neural networks, and gradient-boosted trees. Restricting inputs to physical features (bounce amplitude, bounce width, peak frequency) reduces template leakage, the memorisation of related templates shared across random splits, but does not restore reliable EoS extrapolation. In contrast, a progenitor mass case study shows that classification generalises to unseen rotation speeds, while continuous mass regression compresses predictions towards the catalogue interior. These results demonstrate that while machine learning successfully interpolates within current waveform catalogues, this does not imply robust physical inference for unseen EoS models. Future pipelines should adopt leave-family-out validation, wider simulation coverage, and physics-aware inference frameworks.
↳ astro-ph.HEnucl-th1 citation
08
Collins effect in pion-in-jet production in polarized $pp$ and $e p$ collisions
Carlo Flore · Umberto D'Alesio · Marco Zaccheddu
We study Collins azimuthal asymmetries for pion-in-jet production in polarized proton-proton and lepton-proton collisions. We adopt a hybrid transverse momentum dependent approach, with a collinear configuration for the initial state, and employ the transversity and Collins fragmentation functions extracted from semi-inclusive deep inelastic scattering and $e^{+} e^{-}$ annihilation data. After recalling the good description of the STAR data in $pp$ collisions, which supports the universality of the Collins function, we present predictions for Electron-Ion Collider kinematics, both at leading order and by including the quasireal photon exchange in the Weizsäcker-Williams approximation. This contribution is sizable but does not spoil the dominance of quark-initiated channels. This implies that $ℓ p$ processes allow for a clearer access to the transversity distribution, including its sea-quark component.
↳ hep-phhep-exnucl-th0 citations
09
Recent highlights from the STAR Experiment
Rutik Manikandhan🇺🇸
Understanding the QCD phase structure and the possible existence of a critical point remains one of the central goals of the heavy-ion program at RHIC. In this proceeding, we present recent STAR results across multiple observables that probe different aspects of the hot and dense matter created in Au+Au collisions. These include two-particle transverse momentum correlations of mean transverse momentum, net-proton cumulants up to fourth order, identical-pion femtoscopy, and baryon-strangeness correlations. We also discuss femtoscopic measurements of baryon-baryon pairs, which provide insight into hyperon-nucleon and hyperon-hyperon interactions and the possible formation of strange dibaryon states. Together, these results provide complementary probes of the system's evolution across a wide collision-energy range (sqrt(sNN) = 3-200 GeV), offering new constraints on the QCD equation of state and the location of the QCD critical point.
↳ nucl-exhep-exnucl-th0 citations
10
Double quarkonium production in hadronic collisions at fixed-target experiments
Carlo Flore · Cristian Pisano
We present new results for double quarkonium production in (un)polarized hadronic collisions at fixed-target experiments. Our approach incorporates the transverse momentum dependent factorization in combination with the Color-Singlet Model. We present new analytical expressions for the angular structure of the cross section for the $q q ˉ$ -induced channel, and provide predictions for the unpolarized cross section and transverse single-spin asymmetries for present and future fixed-target experiments at CERN and the LHC.
↳ hep-phhep-exnucl-th0 citations
11
Fierz-complete four-quark interactions and the QCD phase diagram
Zi-ning Wang🇨🇳 · Li-jun Zhou🇨🇳 · Chuang Huang🇩🇪 · Rui Wen🇨🇳 · Shi Yin🇩🇪 · Wei-jie Fu🇨🇳
The dynamics of Fierz-complete four-quark interactions and its influence on the QCD phase diagram have been investigated within the functional renormalization group approach to QCD at finite temperature and densities. It is found that in the vacuum the pion and sigma channels play the overwhelmingly dominant role, and all the other channels are negligible. However, when it is near the critical end point (CEP), the magnitude of four-quark couplings in other channels increases sizably and they become more and more important. In comparison to the single scalar-pseudoscalar channel of four-quark interactions, the dynamics of Fierz-complete four-quark interactions increases a bit the curvature of the phase boundary, and moves the CEP to location of larger baryon chemical potential and smaller temperature.
↳ hep-phnucl-exnucl-th2 citations
12
Hadronic vacuum polarization in hydrogen-like atoms and ions amid the interplay of recoil and finite-size effects
Franziska Hagelstein🇩🇪 · Vadim Lensky🇩🇪 · Bogdan Malaescu🇫🇷 · Vladimir Pascalutsa🇩🇪
Hadronic vacuum polarization (hVP) enters simple atomic systems at a level that is small yet decisive for the precision spectroscopy now underway. We evaluate the hVP contributions to the Lamb shift and the hyperfine splitting (HFS) in ordinary and muonic hydrogen (H and $μ$ H) and hydrogen-like helium-3 ions ( $^{3}$ He $^{+}$ and $μ^{3}$ He $^{+}$ ), using the dispersive data-driven approach and state-of-the-art empirical parametrizations of the $R$ ratio. At the centre of the analysis is the interplay of recoil and finite-size effects: the recoil corrections that dominate the HFS in muonium (Mu), where both constituents are pointlike, are shown to be suppressed by the nuclear elastic form factors (FFs). Our results for the leading hVP contribution to the Lamb shift agree with the literature within uncertainties. Furthermore, we present a first evaluation of the subleading $O (Z^{5} α^{6})$ hVP-finite-size correction, which is by no means negligible in $μ^{3}$ He $^{+}$ . Our results for the hVP contribution to the HFS deviate significantly from all previous evaluations. For the ground-state HFS, we obtain $2.153 (11) μ$ eV in $μ$ H and $- 15.19 (57) μ$ eV in $μ^{3}$ He $^{+}$ , as well as $0.0860 (4)$ kHz and $- 0.476 (17)$ kHz in ordinary H and $^{3}$ He $^{+}$ , respectively. Notably, our result for $μ$ H differs from previous evaluations by roughly ten times the experimental precision anticipated by the upcoming CREMA and FAMU measurements.
↳ physics.atom-phhep-exhep-phnucl-th0 citations
13
Single inclusive hadron and jet production in lepton-hadron scattering
Jian-Wei Qiu🇺🇸 · Kazuhiro Watanabe🇯🇵
We present the first calculation of single inclusive hadron and jet production at large transverse momentum in lepton-hadron scattering in a joint QCD+QED factorization approach. The scattering cross section is factorized into a convolution of infrared-safe hard coefficient functions with universal lepton distribution functions (LDFs) and parton distribution functions (PDFs) of the colliding lepton and hadron, respectively, together with fragmentation functions (FFs) of the observed hadron (or jet). With joint QCD+QED factorization, the DGLAP-type evolution equations for LDFs, PDFs, and FFs necessarily have evolution kernels calculated in both QCD and QED. We derive a default set of LDFs for our calculations and discuss a strategy to extract universal, non-perturbative LDFs from future data. We present our calculations for single inclusive hadron and/or jet production at the energies of Jefferson Lab and the future Electron-Ion Collider.
↳ hep-phhep-exnucl-exnucl-th1 citation
14
Subsolar-mass binary mergers of strange stars and neutron stars: gravitational waves and ejecta
Yong Gao🇩🇪 · Ming-Zhe Han🇩🇪 · Kenta Kiuchi🇩🇪 · Masaru Shibata🇩🇪 · Enping Zhou🇨🇳 · Kenta Hotokezaka🇩🇪
We present the first numerical-relativity simulations of subsolar-mass binary strange star (SS) mergers and compare with binary neutron star (NS) mergers across equations of state, masses, and mass ratios. The self-bound nature of SSs makes them less deformed during the inspiral and keeps a sharp surface up to contact, driving strong shock heating and a large radial bounce that are far weaker in the NS. The more compact SS thus reaches a higher gravitational-wave cutoff frequency $f_{cut}$ before contact but a lower post-merger peak frequency $f_{2}$ . Within each class these frequencies follow quasi-universal relations with the tidal deformability, and their ratio $f_{2} / f_{cut}$ cleanly separates the two classes. Both classes can eject $\sim 1 0^{- 2} M_{⊙}$ of material, neutron-rich for the NS and decompressed quark matter for the SS, a potential source of an electromagnetic counterpart whose observation could test the SS and NS hypotheses for subsolar-mass events.
↳ astro-ph.HEgr-qchep-phnucl-th1 citation

Affiliations

first authorsco-authorsvia INSPIRE