Nuclear Theory·nucl-th

Wednesday·August 6, 2025

10 papers—5 primary·5 cross-listed

01
Variations of the crossover and first-order phase transition curve in modeling the QCD equation of state
Joseph I. Kapusta🇺🇸 · Shensong Wan🇺🇸
Lattice QCD calculations have shown that the transition from hadrons to quarks and gluons is a rapid crossover at $T = 155 - 160$ MeV at vanishing chemical potential. Many model calculations show that the transition is first-order at sufficiently high baryon chemical potential. It is then natural to expect the existence of a critical point where the crossover and first-order phase transition lines meet. We show how to embed a phase boundary that terminates at the critical point in a smooth background equation of state, using several different but closely related criteria, so as to yield the critical exponents and critical amplitude ratios expected of a transition in the 3D Ising and liquid-gas universality class. The crossover curves can be tuned to pass through experimental freeze-out data from heavy ion collisions at RHIC and the LHC. The resulting equations of state can be used in hydrodynamic simulations of these collisions to probe the existence of a critical point and corresponding first-order phase transition.
nucl-thhep-thPRC(2026)·3 citations
02
Response of asymmetric nuclear matter studied with a finite number of particles
M. Li🇯🇵 · F. Marino🇩🇪 · G. Colò🇮🇹 · H. Liang🇯🇵
We investigate the ground-state properties of asymmetric nuclear matter and its response to a static perturbation using the density functional theory framework. Our method, which extends the finite-nucleon-number technique of arXiv:2211.07986 to the case of isospin-asymmetric matter, allows to study the impact of external isoscalar and isovector fields on the system. In particular, the densities and static response functions in the different isospin channels, and as a function of isospin asymmetry, are evaluated. Finite-size effects are discussed by comparing with Random Phase Approximation predictions in the thermodynamic limit. A peculiar non-monotonic behavior of the isovector response function is analyzed.
nucl-thPRC(2026)·0 citations
03
Machine Learning-Driven High-Precision Model for $α$ -Decay Energy and Half-Life Prediction of superheavy nuclei
Qingning Yuan · Panpan Qi · Xuanpen Xiao · Xue Wang · Juan He · Guimei Long · Zhengwei Duan · Yangyan Dai · Runchao Yan · Gongming Yu · Haitao Yang
Based on Extreme Gradient Boosting (XGBoost) framework optimized via Bayesian hyperparameter tuning, we investigated the {\alpha}-decay energy and half-life of superheavy nuclei. By incorporating key nuclear structural features-including mass number, proton-to-neutron ratio, magic number proximity, and angular momentum transfer-the optimized model captures essential physical mechanisms governing $α$ -decay. On the test set, the model achieves significantly lower mean absolute error (MAE) and root mean square error (RMSE) compared to empirical models such as Royer and Budaca, particularly in the low-energy region. SHapley Additive exPlanations (SHAP) analysis confirms these mechanisms are dominated by decay energy, angular momentum barriers, and shell effects. This work establishes a physically consistent, data-driven tool for nuclear property prediction and offers valuable insights into $α$ -decay processes from a machine learning perspective.
nucl-thPhys.Scripta(2026)·4 citations
04
Nonlinear analysis of causality for heat flow in heavy-ion collisions: constraints from equation of state
Victor Roy🇮🇳
The present work investigates the causal parameter space of the Mueller-Israel-Stewart second-order theory for heat-conducting fluids in the Eckart frame for one-dimensional fluid flow in systems with finite baryon density. It is shown that this parameter space is highly constrained and particularly sensitive to the equation of state and second-order transport coefficients. Through numerical analysis of the characteristic equations, the present analysis identifies regions of strong hyperbolicity, weak hyperbolicity, and non-hyperbolicity, mapping the boundaries of causality violation as functions of the heat flux to energy density ratio $q / ε$ and relaxation parameters. The present work also explores the causality conditions using a realistic lattice QCD-based equation of state. Using the Navier-Stokes approximation, an estimate is made of the heat flow magnitude to assess causality criteria for one-dimensional heat conduction in heavy-ion collisions. The present calculations reveal unrealistically large heat flux values ( $∣ q ∣/ ε \approx 330$ -- $811$ ) for typical RHIC conditions when using thermal conductivity estimates from kinetic theory models, suggesting either significant overestimation of transport coefficients or breakdown of the fluid approximation in these extreme conditions. The pressure gradient corrections reduce the heat flow by approximately 15\% but do not resolve the causality concerns.
nucl-thhep-phPRC(2026)·2 citations
05
Machine learning the single- $Λ$ hypernuclei with neural-network quantum states
Zi-Xiao Zhang🇨🇳 · Yi-Long Yang🇨🇳 · Wan-Bing He🇨🇳 · Peng-Wei Zhao🇨🇳 · Bing-Nan Lu🇨🇳 · Yu-Gang Ma🇨🇳
Single- $Λ$ hypernuclei are the most straightforward extension of atomic nuclei. A thorough description of baryonic system beyond first-generation quark sector is indispensable for the maturation of nuclear $ab$ $ini t i o$ methods. This study pioneers the application of neural-network quantum states to hypernuclei, with trainable parameters determined by variational Monte Carlo approach (VMC-NQS). In order to reduce the numerical uncertainty and treat the nucleons and hyperons in a unified manner, spinor grouping (SG) method is proposed to analytically integrate out isospin degrees of freedom. A novel spin purification scheme is developed to address the severe spin contamination occurring in standard energy minimization due to the weakly bound characteristic of light single- $Λ$ hypernuclei. The energy spectrum of $s$ -shell hypernuclei is computed with one-thousandth level accuracy and benchmarked against existing stochastic variational results, showing superior performance. By comparing two different sets of Hamiltonian based on pionless effective field theory (pionless EFT), we choose an optimal model and further carry out calculations of selected $p$ -shell charge-symmetric hypernuclei with mass number up to 13, exhibiting satisfactory consistency with experimental results. Our findings underscore the potential of VMC-NQS family in approaching exact solution of few-body systems and the accuracy of pionless EFT in modeling hypernuclei. This is crucial for understanding hyperon-nucleon-nucleon and hyperon-hyperon-nucleon interactions, providing a powerful tool for precisely predicting the properties of multi-strangeness hypernuclei.
nucl-thPLB(2026)·7 citations
06
Second-order renormalized Hamiltonian of Yukawa theory
Kamil Serafin🇺🇸 · Carter M. Gustin🇺🇸 · Peter J. Love🇨🇦
Using the renormalization group procedure for effective particles (RGPEP) we calculate the effective Hamiltonians in the theory of a fermion field coupled to a scalar field via the Yukawa interaction. The theory is renormalized by the addition of counterterms. Necessary counterterms are determined by computing matrix elements of the effective Hamiltonian. All calculations are performed up to the second order in the expansion in powers of the coupling constant. Renormalized effective Hamiltonians are well-defined symmetric forms acting in the Fock space as opposed to the renormalized bare Hamiltonian, which is not well-defined without regularization. We introduce computational techniques that should streamline higher-order calculations and may be of independent interest.
↳ hep-phnucl-thPRD(2025)·3 citations
07
Lattice results for the equation of state in dense QCD-like theories
Etsuko Itou🇯🇵
We review recent progress in Monte Carlo simulations of dense two-color QCD (QC $_{2}$ D), focusing on the phase diagram, the equation of state, and the sound velocity in the low-temperature regime. In three-color QCD at finite density, especially at low temperatures, the notorious sign problem makes lattice Monte Carlo simulations intractable. In contrast, QC $_{2}$ D is free from this issue due to the pseudoreality of the quark representation. Recent independent lattice studies have revealed unexpected phenomena through first-principles calculations of the phase structure and thermodynamics. A particularly notable finding is that the sound velocity exceeds the so-called conformal (holography) bound, $ c_s^2/c^2 \le 1/3 $, which had not been observed in QCD-like theories at finite temperature. In this review, we focus primarily on results from a series of works by our group~\cite{Iida:2019rah, Iida:2020emi,Iida:2022hyy, Ishiguro:2021yxr, Iida:2024irv}, along with related studies in dense QC $_{2}$ D and three-color QCD with isospin chemical potential. We discuss the possibility and physical implications of conformal bound violation even for three-color dense QCD, together with insights from effective model analyses and recent observations of neutron stars.
↳ hep-lathep-phhep-thnucl-thUniverse(2025)·11 citations
08
Probing non-perturbative QCD aspects on particle production in pp collisions with forward-backward correlations using \texttt{PYTHIA8}
Rohit Agarwala🇮🇳 · Kalyan Dey🇮🇳
We employ PYTHIA8 simulations to study forward-backward (FB) correlations in pp collisions at LHC energies, probing non-perturbative QCD dynamics via color reconnection (CR) and QCD radiation (ISR/FSR). Using \texttt{PYTHIA8} (v8.311) under ALICE/ATLAS kinematics, we analyze: extensive: FB multiplicity ( $b_{corr}^{mult}$ ) and summed $p_{T}$ ( $b_{corr}^{\sum p_{T}}$ ) correlations; intensive: FB mean $p_{T}$ ( $b_{corr}^{p_{T}}$ ) correlations; and \textit{strongly intensive:} $Σ_{N_{F} N_{B}}$ quantity in symmetric pseudorapidity intervals, validated against available experimental data. Systematic studies of $b_{corr}^{mult}$ as functions of $η_{gap}$ , $η_{sep}$ , and $η$ - $φ$ sectors show MPI-based CR (ranges 3.6, 5.4) and QCD Color Rope significantly improve agreement with data. ISR/FSR critically influence $b_{corr}^{mult}$ and $b_{corr}^{\sum p_{T}}$ , with ISR dominant than FSR. Disabling ISR/FSR fails to replicate $η_{gap}$ -dependent trends. Further, $b_{corr}^{\sum p_{T}}$ shows minimal CR-range sensitivity but the correlation strength increases when CR is disabled. Intensive quantity, $b_{corr}^{p_{T}}$ , exhibit the opposite behavior to extensive observables i.e. the magnitude of $b_{corr}^{p_{T}}$ increases with the increase of CR strength, highlighting the distinct influence of CR on intensive versus extensive observables. Its azimuthal dependence indicates that parton showers drive short-range correlations. The analysis of the strongly intensive quantity as a function of pseudorapidity gap indicates that FSR plays a dominant role at larger gaps, in contrast to the behavior observed in FB multiplicity correlations.
↳ hep-phnucl-th0 citations
09
New computational methods in lattice gauge theory -- quantum computation and tensor networks
Etsuko Itou🇯🇵
Lattice QCD calculations have been conducted using large-scale classical computers based on the Lagrangian formalism of field theory for the past 40 years. On the other hand, the advent of quantum computers has brought increasing attention to first-principles computational methods based on the Hamiltonian formalism compatible with these machines. In this talk, we discuss recent results on how to calculate hadronic properties using the Hamiltonian formalism.
↳ hep-lathep-phnucl-thquant-phPoS(2026)·2 citations
10
Hyperon spin correlation in high-energy heavy-ion collisions
Xin-Li Sheng🇮🇹 · Xiang-Yu Wu🇨🇦 · Dirk H. Rischke🇩🇪 · Xin-Nian Wang🇨🇳
Recent experimental data show an unexpectedly large spin alignment of $ϕ$ mesons in high-energy heavy-ion collisions, which can be explained by short-distance fluctuations of strong-force fields (vector $ϕ$ fields) within the constituent-quark model. We calculate the hyperon spin correlations within the same model, taking into account hydrodynamic effects and a $ϕ$ field fluctuating in space-time according to a Gaussian distribution. The $Λ Λ ˉ$ spin correlation induced by the $ϕ$ field is shown to be negative as opposed to that of $ΛΛ$ or $Λ ˉ Λ ˉ$ . We thus propose a new net spin-correlation observable as a sensitive probe to separate strong-force effects from hydrodynamic ones. With the strength of the field fluctuations extracted from the observed $ϕ$ spin alignment, we predict the collision-energy dependence of the hyperon spin correlations and also investigate the dependence of the net spin correlation on azimuthal-angle and rapidity difference.
↳ hep-phnucl-thPRL(2026)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE