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Physics Nuclear Theory

nucl-th Watch Nuclear Theory

Tuesday 18 August

Nuclear Theory

Generative artificial intelligence for reconstructing neutron-star matter

Julia Yu. Panteleeva, Herzallah Alharazin and Evgeny Epelbaum

Neutron-star cores hold the only known matter in the universe that is simultaneously cold and strongly interacting, compressed beyond nuclear density into a state of unknown composition. The equation of state links stellar masses, radii and tidal deformabilities to this regime, but recovering this key quantity from sparse observations is an ill-posed inverse problem. Existing analyses bury a prior in a fixed functional form, unevenly weighting admissible solutions and biasing the result. We reconstruct the equation of state with a denoising diffusion model that keeps prior, physics and data separate: it learns an inspectable, physically motivated prior anchored to first-principles nuclear theory, while perturbative-QCD and astrophysical constraints are imposed exactly. Future measurements therefore will update the posterior by reweighting alone, without retraining or resampling. The inferred radius of 12.6 km and tidal deformability of 469 at 1.4 solar masses reproduce Gaussian-process and heavy-ion-informed inferences despite a far broader prior. We find near-conformal but still stiff matter in the heaviest stars, consistent with a gradual hadron-quark crossover and disfavouring a strong first-order phase transition. More broadly, coupling a learned prior to exactly enforced physics establishes a template for ill-posed inverse problems where theory and data constrain different regions.
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Nuclear Theory · Cross-listed from astro-ph.HE

Density-induced dark-baryon conversion in $\Delta-$admixed hypernuclear neutron stars

Niyar Prabhat Kalita, Vivek Baruah Thapa, Bhanu Prakash Pant et al. (+2 more)

We investigate density-induced conversion of neutrons into a neutral dark baryon $\chi$ in cold, charge-neutral, $\beta$-equilibrated neutron-star matter containing hyperons and all $\Delta(1232)$ quartet. The hadronic sector is modeled within a density-dependent covariant density-functional framework using the DDME2 parametrization. A scalar Higgs portal is included as a possible interaction channel between the visible and dark sectors, although its mean-field contribution is negligible for the couplings adopted here. Unlike fixed dark-matter admixture models or scenarios in which nucleon-to-DM conversion is driven by Higgs exchange, the $\chi$ abundance is determined self-consistently from chemical equilibrium and baryon-number conservation. We find that hyperons and $\Delta$ resonances alter the neutron chemical potential, delay the onset of $\chi$, and suppress its abundance relative to nucleonic matter. This competition induces characteristic changes in the equation of state, particle fractions, sound speed, and adiabatic index. For $m_\chi=1250$, $1300$, and $1400$ MeV, the maximum masses of the complete $N+Y+\Delta+\chi$ configurations are $1.806$, $1.899$, and $2.024,M_\odot$, respectively, indicating that the massive-pulsar constraint disfavors the lighter dark-baryon benchmarks. The radial profiles further show that for $m_\chi=1400$ MeV, $\chi$ is confined to the inner core of the most massive stars, while canonical configurations remain essentially unaffected. Thus, the stellar modifications arise primarily from conversion-induced rearrangement of the equilibrium composition rather than from Higgs-mediated interactions. These results highlight the importance of treating conventional non-nucleonic degrees of freedom and density-generated dark baryons on an equal footing when assessing the astrophysical viability of dark-sector extensions of dense matter.
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All authors Niyar Prabhat Kalita, Vivek Baruah Thapa, Bhanu Prakash Pant, Anil Kumar, Partha Konar

Nuclear Theory · Cross-listed from hep-ph

From the universal Lindblad equation to Boltzmann equations: in-QGP quarkonium dynamics

Aoumeur Daddi Hammou and Pol Bernard Gossiaux

Recently, a set of coupled singlet-octet universal Lindblad equations (ULEs) was derived within the framework of non-relativistic QCD (NRQCD) to describe quarkonium dynamics in the quark-gluon plasma (QGP). These equations provide a unified quantum description spanning the quantum Brownian and quantum optical regimes. In this work, we further develop this framework and establish its connection with semiclassical transport. We first derive the universal Lindblad equations within the potential non-relativistic QCD (pNRQCD) effective field theory and show that they coincide with the small-dipole limit of the NRQCD ULEs. We then derive the semiclassical limit of the NRQCD ULEs, obtaining a set of coupled singlet-octet Boltzmann equations. To our knowledge, this is the first derivation of Boltzmann transport equations directly from the universal Lindblad framework. The resulting equations are valid beyond the small-dipole approximation, allowing the evolution of heavy-quark pairs from compact to widely separated configurations. Taking their small-dipole limit allows a direct comparison with the Boltzmann equations of Yao et al. [Phys. Rev. D 99, 096028 (2019)], which were derived within pNRQCD from the Davies secular equation, relying on the rotating-wave approximation (RWA). While the singlet equations are found to be in near-complete agreement, the octet equation contains an additional collision term describing transitions within the continuum of octet scattering states, which is absent from the RWA-based derivation. Finally, we derive the leading quantum correction to the singlet Boltzmann equation. Our results establish a more general and systematic theoretical foundation for the semiclassical transport description of quarkonium in the QGP.
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Monday 17 August

Nuclear Theory · Cross-listed from hep-ph

Closed-form expressions for tree-level gluon-gluon scattering: a framework for obtaining theoretical systematic uncertainties for jet-medium Monte Carlo simulations

Lukas Opitz, Hemanth Regi and Gojko Vujanovic

Modern Bayesian theory-to-data comparisons for jet-medium interactions, such as [Phys. Rev. C 111,054913 (2025)], are lacking the careful accounting of theoretical systematic uncertainties included within their uncertainty budget. Tree-level gluon-gluon scattering is revisited to establish a framework capable of quantifying theoretical systematic uncertainties to be used in Bayesian jet-medium constraints. The behavior of tree-level scattering in thermal QCD is examined in detail, finding deviations away from the commonly used approximations. Deviations in the scattering rate affect jet-medium transport coefficients at the partonic level, leading to a more intricate kinematic dependence for $\hat q$ and $\hat e$ than, say, the well-known logarithmic behavior. These deviations away from well-known behavior are used to estimate theoretical systematic uncertainties in Bayesian analysis.
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Nuclear Theory · Cross-listed from hep-ph

The high-energy behavior of tree-level scattering in finite-temperature QCD: estimates of theoretical systematic uncertainty in jet-medium Monte Carlo simulations

Lukas Opitz, Hemanth Regi and Gojko Vujanovic

We examine the behavior of tree-level scattering in thermal QCD at high energies and find significant deviations away from the commonly used approximations [Phys. Rev. D 44, 1298 (1991), Phys. Rev. D 44, R2625 (1991), Phys. Rev. D.77, 014015 (2008), Phys. Rev. D. 77.114017 (2008)]. These deviations in the scattering rate also affect jet-medium transport coefficients at the partonic level, leading to a different kinematic dependence of the transverse momentum broadening per unit length $\hat{q}$. As scattering rates and $\hat{q}$ are used by large-scale Monte Carlo simulations of jets in the quark-gluon plasma (QGP), such as [Phys. Rev. C 111,054913 (2025)], current constraints on $\hat q$ are biased owing to the approximations used therein. Besides theoretically improving $\hat q$, the differences between the $\hat q$ herein and the approximate $\hat q$ used in jet Monte Carlo simulations are used to construct a theoretical systematic uncertainty, which in turn can be employed to devise a covariance matrix for $\hat q$ and enables updating the uncertainty bands on $\hat q$ obtained by Bayesian analysis.
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Nuclear Theory · Cross-listed from nucl-ex

Accurate Charge Radius Measurement of $^{14}$C Confronts Ab Initio Theory

Kristian König, Patrick Müller, Tobias Gesser et al. (+11 more)

Located at the neutron shell closure $N = 8$, the long-lived radioactive isotope $^{14}$C plays a critical role in geochronology and nuclear structure studies. Despite its widespread use, the nuclear charge radius of $^{14}$C has remained less precisely known compared to its stable counterpart $^{12}$C. Here, we report a high-precision determination of the $^{14}$C charge radius using collinear laser spectroscopy at the COALA setup at TU Darmstadt, improving upon the precision of previous muonic measurements by a factor $5$ and revealing a $1.9\sigma$ discrepancy of combined uncertainty, indicating a likely underestimated uncertainty in the muonic determination. This measurement challenges state-of-the-art ab initio nuclear theory calculations, including auxiliary field diffusion Monte Carlo, the valence-space in-medium similarity renormalization group, and the no-core shell model, augmented by neural-network techniques. With $^{12}$C and $^{14}$C now forming one of the most precisely characterized even-even isotope pairs, these results also enable improved QED tests.
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All authors Kristian König, Patrick Müller, Tobias Gesser, Emily Burbach, Stefano Gandolfi, Matthias Heinz, Phillip Imgram, Alessandro Lovato, Pieter Maris, Takayuki Miyagi, Wilfried Nörtershäuser, Robert Roth, Julien Spahn, Achim Schwenk

Nuclear Theory · Cross-listed from cond-mat.quant-gas

Hydrodynamization in 1D Bose gases at nonzero temperature

Jeff Leiberton and Marcos Rigol

Hydrodynamization refers to the remarkably rapid process in relativistic heavy-ion collisions by which hydrodynamic descriptions become applicable. Following the observation of analogous behavior in ultracold one-dimensional (1D) Bose gases, hydrodynamization has been conjectured to be a universal dynamical phenomenon in quantum systems following high-energy quenches. Theoretical studies in this cold-atom setting have so far been restricted to quenches from ground states. Here we study how nonzero temperatures affect hydrodynamization. Specifically, using a homogeneous 1D gas of hard-core bosons, we explore how the initial temperature affects the timescales associated with hydrodynamization and prethermalization following a Bragg-pulse quench. We find that while the hydrodynamization coherence time remains unchanged, increasing temperature shortens both the damping time of the hydrodynamization oscillations and the prethermalization time. We argue that this is mainly the result of the broadening of the initial rapidity distribution, and introduce a nonzero-temperature dephasing time defined in terms of the extent of the rapidity distribution.
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Nuclear Theory

Implementation of the Moments Method in TALYS: Sensitivity of $^{56,57}$Fe$(n,\gamma)$ observables to shell model nuclear level densities

Lucas Chouinard and Sofia Karampagia

The Moments Method (MM), a statistical spectroscopy framework built upon configuration interaction shell model Hamiltonians that enables shell model descriptions of nuclear level densities without requiring full diagonalization of the many body Hamiltonian, is implemented in the TALYS reaction code to investigate the sensitivity of Hauser-Feshbach calculations for the $^{56}$Fe$(n,\gamma)^{57}$Fe and $^{57}$Fe$(n,\gamma)^{58}$Fe reactions to the nuclear level density input. Spin- and parity-dependent MM level densities calculated in the pf shell are interfaced with TALYS and compared with the phenomenological and microscopic level density models available in the code. To construct TALYS-ready inputs, the MM level densities are extended to higher excitation energies using a back shifted Fermi gas continuation together with an experimentally constrained prescription for opposite-parity states. A sensitivity band for the MM calculations is estimated by varying a single parameter governing the statistical reconstruction of the level density. Neutron capture cross sections, Maxwellian averaged cross sections, and reaction rates are compared with evaluated ENDF/B-VIII.0 data and recommended KADoNiS and JINA-CEE values to assess the relative importance of the nuclear level density and $\gamma$-ray strength function inputs. The calculations show that the observables are considerably more sensitive to the choice of $\gamma$-ray strength function than to the MM level density variation considered here, while the MM-based results remain in good agreement with evaluated cross sections and recommended astrophysical reaction rates.
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Nuclear Theory · Cross-listed from hep-lat

Quantum Simulation of QCD in Axial Gauge

Xiaojun Yao

We study quantum simulation of SU(3) non-Abelian gauge theory dynamically coupled with fundamental fermions in $3+1$ dimensions by employing the lattice Hamiltonian in axial gauge that avoids Gauss's law constraints. The temporal component of the gauge field is analytically solved in terms of independent field degrees of freedom and a lattice regulated Green's function. The axial gauge condition is trivially maintained in time evolution, even under Trotterization. The gauge field degrees of freedom are expressed in the local field basis and can be efficiently transformed into the canonical conjugate momentum basis by local quantum Fourier transforms. We prove the number of qubits needed for describing all states up to an energy $E$ with an accuracy $\epsilon$ on a lattice of volume $V$ at bare coupling $g$ is bounded as $16n_A V + 12n_f V$, where $n_A \approx \log_2 (\frac{64 E' V^{4/3}}{\pi^2\epsilon} + \frac{32\sqrt{2}g n_f E'^{1/2} V^{7/6}}{\sqrt{3}\pi^3\epsilon^{1/2}} ) $ is the number of qubits needed for each independent gauge field per site with a shifted energy $E'$, and $n_f$ denotes the number of fermion flavors. We then analyze a quantum algorithm for time evolution that is based on Trotterization, quantum Fourier transform, and Jordan-Wigner transformation, for which quantum circuits can be explicitly constructed under arbitrary gauge field truncation and digitization. We find the numbers of CNOT and single-qubit rotation gates both scale as $O(n_A^4 V^{4/3}) + O(V^{5/3})$ per Trotter step for fixed $n_f\leq 6$. We conclude that quantum resources needed for simulating real-time dynamics of lattice QCD scale polynomially with volume, energy, time, accuracy, and bare Hamiltonian parameters.
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Nuclear Theory

Nuclear Drip Line and the Composition of Supernova Matter

S. Maity and S. Mallik

The nuclear drip line plays a crucial role in determining the composition of matter under extreme astrophysical conditions. In core-collapse supernovae and neutron-star crusts, matter is driven far from saturation density and nuclear stability; nuclei coexist with a sea of free neutrons, an effect that is present even at zero temperature in neutron-star crusts and becomes more pronounced in the hotter, neutron-rich supernova environment. This makes a careful treatment of drip-line physics essential for a realistic description of the equation of state and composition. In this work, the influence of the nuclear drip line on the baryonic composition of supernova matter is investigated within the framework of nuclear statistical equilibrium (NSE). The composition is evaluated in terms of free nucleons, light clusters, and heavy nuclei at finite temperature and global sub-saturation densities. The results indicate that, at low proton fractions and higher densities, the inclusion of nuclei beyond the drip line enhances the formation of extremely neutron-rich light clusters, leading to a significant reduction in the free-neutron density and the charge fraction of heavy nuclei. These findings demonstrate that drip-line physics has a significant impact on the composition of supernova matter and should be carefully incorporated in supernova modeling and nucleosynthesis studies.
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Nuclear Theory · Cross-listed from hep-th

Chiral Soliton Lattices under Magnetic Fields and Rotation: a Holographic Analysis

Markus A. G. Amano, Minoru Eto, Muneto Nitta et al. (+1 more)

We study the chiral soliton lattice (CSL) in rotating QCD matter under a background magnetic field within holographic QCD. We show that rotation can be incorporated as a background gauge field and that the CSL in rotating matter becomes a ground state in the gravity dual. We also provide a brane interpretation of the CSL under a magnetic field and rotation. Solving the bulk equations, we derive an effective Hamiltonian where the meson decay constant $\tilde{f}$ emerges as an anisotropic, field-dependent matrix. Furthermore, we discuss the thermodynamic properties of the ground state in rotating matter and study its equation of state.
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All authors Markus A. G. Amano, Minoru Eto, Muneto Nitta, Shin Sasaki

Nuclear Theory

Ab initio evidence for surface-dominated antiproton annihilation in ${}^4 \mathrm{He}$

Alireza Dehghani, Guillaume Hupin, Sofia Quaglioni et al. (+1 more)

Low-energy antiproton beams at CERN/AD open the possibility of probing exotic nuclear structure through annihilation at the nuclear surface. The use of antiprotons as the probe for the nuclear surface is based on the assumption that the annihilation takes place at the periphery of the target. We test this idea for the lightest tightly bound nucleus, i.e., ${}^4 \mathrm{He}$, using the ab initio no-core shell model combined with the resonating group method (NCSM/RGM), adapted to antiproton-nucleus dynamics. After validating our microscopic calculations against available atomic and scattering data, we use the microscopic annihilation density to examine where annihilation occurs inside the antiprotonic atom. We find that the annihilation peaks in the tail of the ${}^{4}\mathrm{He}$ density, around $r\approx 2$ fm, and is strongly suppressed in the nuclear interior. Although this density is representation dependent, a similarity renormalization group (SRG) analysis of the NCSM/RGM Hamiltonian shows that the low-energy annihilation strength remains localized at large intercluster distances. These results support the phenomenological picture underlying antiprotonic-atom experiments: in a tightly bound system such as ${}^{4}\mathrm{He}$, antiproton annihilation is predominantly peripheral and is therefore sensitive to the nuclear-density tail.
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All authors Alireza Dehghani, Guillaume Hupin, Sofia Quaglioni, Petr Navrátil

Nuclear Theory · Cross-listed from nucl-ex

Probing the Size of Neutron and Proton Single-Particle Orbitals from Nucleon Knockout Reactions

M. Enciu, A. Obertelli, P. Doornenbal et al. (+83 more)

The size of neutron and proton single-particle orbitals of $^{52}$Ca, $^{53}$Ca, $^{54}$Ca, and $^{55}$Sc were investigated via nucleon knockout reactions at $\sim$ 230 MeV/nucleon. The determination method is based on the measured fragment momentum distributions in $(p,pn)$ and $(p,2p)$ reactions, which are shown to be sensitive to the spatial extension of the wave function of the knocked-out nucleon, interpreted within the distorted wave impulse approximation (DWIA) framework. A systematic sensitivity study is carried out for the $(p,pn)$ recoil-momentum distribution method and is presented in this work. The experimental momentum distributions are compared to state-of-the-art mean field and $ab$ $initio$ in-medium similarity renormalization group and self-consistent Green's function calculations in combination with DWIA reaction theory calculations. Based on this work, the 1$p$ neutron orbitals are consistently found $0.48-0.78$ fm larger than the $0f_{7/2}$ neutron orbitals in $^{52-54}$Ca, while the size evolution of the valence proton orbitals remains inconclusive due to the large associated statistical uncertainties.
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All authors M. Enciu, A. Obertelli, P. Doornenbal, C. Barbieri, S. Brolli, M. Heinz, W. Horiuchi, T. Inakura, W. H. Long, T. Miyagi, F. Nowacki, K. Ogata, A. Poves, A. Schwenk, K. Yoshida, N. L. Achouri, H. Baba, F. Browne, D. Calvet, F. Château, S. Chen, N. Chiga, A. Corsi, M. L. Cortés, A. Delbart, J-M. Gheller, A. Giganon, A. Gillibert, C. Hilaire, T. Isobe, T. Kobayashi, Y. Kubota, V. Lapoux, H. N. Liu, T. Motobayashi, I. Murray, H. Otsu, V. Panin, N. Paul, W. Rodriguez, H. Sakurai, M. Sasano, D. Steppenbeck, L. Stuhl, Y. L. Sun, Y. Togano, T. Uesaka, K. Wimmer, K. Yoneda, O. Aktas, T. Aumann, L. X. Chung, F. Flavigny, S. Franchoo, I. Gasparic, R.-B. Gerst, J. Gibelin, K. I. Hahn, D. Kim, Y. Kondo, P. Koseoglou, J. Lee, C. Lehr, P. J. Li, B. D. Linh, T. Lokotko, M. MacCormick, K. Moschner, T. Nakamura, S. Y. Park, D. Rossi, E. Sahin, P-A. Söderström, D. Sohler, S. Takeuchi, H. Toernqvist, V. Vaquero, V. Wagner, S. Wang, V. Werner, X. Xu, H. Yamada, D. Yan, Z. Yang, M. Yasuda, L. Zanetti

Nuclear Theory

Probing Vortex {\gamma} Photons via Nuclear Resonance Fluorescence

H. L. Chen, Y. F. Niu and F. Q. Chen

High-energy vortex {\gamma} photons offer unique prospects in nuclear physics, astrophysics, and strong-field physics, owing to their distinctive topological structure. Yet, their hallmark effects are erased in macroscopic targets, the only practical regime to date, when probed via the total transition probability of photoabsorption. Here we show that nuclear resonance fluorescence (NRF) circumvents this limitation. Using a Bessel-mode description, we demonstrate that for macroscopic targets, the target-averaged angular distribution of scattered photons retains a distinct dependence on the vortex polar angle, which emerges as the sole surviving vortex signature. Moreover, by scanning the vortex polar angle instead of the detector angle, we show that NRF can extract the angular momentum of nuclear excited states in a fixed-geometry setup. The vortex polar angle, a new degree of freedom in NRF, not only provides a direct quantitative diagnostic for vortex {\gamma} beams at the MeV energy scale, but also opens a new avenue for exploring orbital angular momentum-induced quantum phenomena in photonuclear physics.
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Nuclear Theory · Cross-listed from hep-ph

Rotation modified QCD equation of state across crossover at finite chemical potential

S. Ipsita Sahoo, Sanjeebani Biswal, Dipanwita Dutta et al. (+1 more)

It is well-established that at low baryon chemical potential, the transition from the confined hadronic phase to the deconfined partonic phase is a smooth crossover rather than a first or second-order phase transition. We develop a thermodynamically consistent hybrid equation of state to study the effect of global rotation on the equation of state across the QCD crossover that interpolates the hadronic and partonic phases. The temperature dependence of normalized thermodynamic observables, such as entropy density ($s/T^3$), pressure ($P/T^4$), energy density ($\varepsilon/T^4$), specific heat ($C_V/T^3$), and the square of speed of sound ($c_s^2$) in presence of rotation are investigated. The effect of non-zero chemical potential on thermodynamic quantities in presence of rotation is also studied. Our results show that increasing chemical potential enhances the thermodynamic quantities, whereas rotation suppresses them in the crossover region. Further, we investigate the effect of rotation on the conserved numbers susceptibilities and their correlations as a function of temperature. The susceptibilities and their correlations exhibit a systematic enhancement with increase in rotation in both the hadronic and partonic phases. These findings provide new insights into the interplay between rotation and QCD thermodynamics, which can have important implications for rapidly rotating strongly interacting matter produced in ultra-relativistic heavy-ion collisions.
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All authors S. Ipsita Sahoo, Sanjeebani Biswal, Dipanwita Dutta, Dipak Kumar Mishra

Nuclear Theory · Cross-listed from hep-lat

Jump-Diffusion Stochastic Quantization for Euclidean Lattice Field Theories

Alexander Rothkopf

We construct the natural generalization of stochastic quantization (in the Markovian sense) by considering jump-diffusion processes. This class of stochastic processes exhibits non-continuous paths, so-called Lévy flights. In the presence of jumps, action landscapes with barriers can be efficiently explored, improving and even restoring ergodicity where traditional diffusion approaches become inefficient. We explore different strategies for constructing efficient jump updates, which we deploy to address the benchmark problem of topological freezing in 2d U(1) gauge theory.
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Nuclear Theory · Cross-listed from gr-qc

Limiting cases of second-order moments of relativistic stars and their universality

Koutarou Kyutoku

Extending the work presented in a workshop “From Quarks to Neutron Stars: Insights from kHz gravitational waves”, we discuss some limiting cases of the moment of inertia, tidal deformability, and spin-induced quadrupole moment for relativistic stars. First, conjecturing that a hierarchy of the length scale is the key to proposed universality among these second-order moments, we revisit the relation for incompressible relativistic stars (known as Schwarzschild's interior solution) as a candidate of the possible stiff limit. Second, we present the limiting form for the weak-field limit. In particular, we demonstrate how relativistic computations of tidal deformation are related to the traditional Newtonian counterpart, which might not have been presented explicitly in the literature.
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Nuclear Theory

Scalable nuclear shell model calculations on noisy quantum computers

Durgesh Pandey, Ankit Kumar Das and P. Arumugam

The exact diagonalization of the nuclear shell model scales exponentially, leading to severe memory bottlenecks in classical high-performance computing (HPC). While hybrid quantum algorithms like the Variational Quantum Eigensolver (VQE) aim to overcome these limits, their deep quantum circuits and iterative feedback loops are susceptible to substantial noise inherent in the current Noisy Intermediate-Scale Quantum (NISQ) hardware. This noise renders several algorithms, such as the VQE, impractical for large-scale calculations despite sophisticated noise-mitigation techniques. As a pragmatic approach tolerant to these issues, we apply the Sample-based Quantum Diagonalization (SQD) framework to nuclear shell models for the first time. Using $^{38}\text{Ar}$ as a benchmark to confirm the numerical accuracy, we extend SQD to $^{32}\text{Mg}$, solving a nuclear shell-model Hamiltonian whose underlying Hilbert space cannot be directly diagonalized using conventional classical methods in a given HPC system. We present a systematic comparison of SQD with standard variational quantum schemes and exact classical solvers. By leveraging NISQ hardware connected via the cloud to classical HPC clusters, the SQD-based scheme could outperform conventional supercomputers in memory scaling and total execution time, enabling more rigorous large-scale shell model calculations.
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Nuclear Theory

Origin and limits of intermediate-mass dilepton thermometry

Lipei Du

We identify the physical origin and limits of intermediate-mass dilepton thermometry in relativistic heavy-ion collisions. Using a controlled expanding-fireball framework with thermal dilepton rates, we show that the local inverse-slope parameter of the invariant-mass spectrum follows, to percent-level accuracy, the emission-weighted harmonic mean of the temperatures contributing to the spectrum. As the thermal-stage initial temperature increases, the temperatures sampled by the radiation shift upward with the overall thermal scale, causing their harmonic mean to track the initial temperature closely. This provides the physical basis for the strong inverse-slope–initial-temperature correlation, while the resulting mapping remains nonuniversal: changes that only rescale the amount of radiation leave it unchanged, whereas changes in the cooling history or source composition redistribute the radiation among different temperatures and modify the response. The mapping is nevertheless nearly linear over the temperature range studied here. Because different invariant-mass windows weight the emission history differently, source scenarios with the same inverse-slope parameter in $1<M<3~{\rm GeV}$ develop different inverse slopes in harder mass windows. Intermediate-mass dilepton spectra therefore provide a quantitative but nonuniversal probe of the early thermal history, while measurements in multiple mass windows, when confronted with realistic calculations, can provide additional constraints on the thermal evolution and early electromagnetic source content.
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Nuclear Theory

Deep-learning classification of physically admissible nuclear-matter equations of state

Ahmed Abuali, Micheal Kahangirwe, Francesco Di Clemente et al. (+3 more)

Thermodynamic stability and causality impose fundamental constraints on the equation of state (EoS) of nuclear matter. Verifying these constraints conventionally requires calculating quantities such as the specific heat, baryon-number susceptibility, and speed of sound, which can become computationally expensive when many candidate EoSs must be examined. We investigate whether the normalized pressure surface, $Q(T,\mu_B)=P(T,\mu_B)/T^4$, alone contains sufficient information to determine the physical admissibility of an EoS. We develop a supervised convolutional neural network (CNN) that uses only this pressure representation to classify EoSs as physically admissible or inadmissible. The network is provided with training labels obtained from direct thermodynmaic stability and causality check and its does not get any information about the parameters of the underlying EoS framework. For EoSs generated within an Ising-mapping framework, the model achieves $97.65%$ accuracy on unseen test data. Applied independently to EoSs from a distinct holographic framework, it achieves perfect classification of the test set. These results show that pressure surfaces contain geometric signatures of thermodynamic stability and causality violations that can be learned directly by a CNN. Because the classifier relies only on the pressure surface, it avoids evaluating higher-order thermodynamic observables during inference and is largely independent of the EoS-generation framework. When the pressure surface is supplied as a two-dimensional array, the machine-learning validation is approximately 20 times faster than direct validation. Our results establish a fast, framework-independent approach for identifying physically admissible EoSs directly from their pressure surfaces.
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All authors Ahmed Abuali, Micheal Kahangirwe, Francesco Di Clemente, Vianney E Diaz-Barraza, Jorge A Munoz, Claudia Ratti

Sunday 16 August

Nuclear Theory · Cross-listed from hep-ph

Universality and Kinematic Dependence of Hadronization Effects in DIS Global Event Shapes

Radja Boughezal, Haotian Cao, Zhong-Bo Kang et al. (+3 more)

We propose a unified framework for a combined global analysis to constrain leading hadronization effects across the 1-Jettiness class of global event shapes for Deep Inelastic Scattering (DIS). We show that for the subclass of jet-based event shapes where the leading jet direction is determined dynamically event-by-event, the leading hadronization effects can acquire a non-trivial dependence on the hard scattering kinematics. However, this dependence is explicitly calculable, allowing for universality of leading hadronization effects in the 1-Jettiness class. The non-trivial kinematic dependence provides an independent lever arm for simultaneously constraining hadronization effects in the jet-based and DIS thrust event shapes. This universality, combined with the kinematic lever arm, could allow for including the typically ignored peak region, where hadronization effects are most severe, in precision extractions of the strong coupling. We demonstrate the need for such a unified treatment of hadronization effects through comparisons of theoretical predictions with simulation data.
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All authors Radja Boughezal, Haotian Cao, Zhong-Bo Kang, Xiaohui Liu, Sonny Mantry, Frank Petriello

Nuclear Theory

Renormalization Group Analysis of Pairing Instabilities in Nuclear Fermi Liquids

Yang Xiao, Yixin Guo and Youngman Kim

A nuclear Fermi liquid exhibits competing pairing instabilities in different spin, isospin, and orbital channels. In a Fermi-surface renormalization group (RG) treatment, the channel that develops a pole first is determined not only by its tree-level attraction but also by its one-loop RG coefficient. We illustrate this mechanism in a minimal $S/P$-wave model. A spherical Fermi surface establishes the reference competition between the lowest even- and odd-parity interactions. Axial deformation changes the relevant Fermi-surface integrals and lifts the degeneracy between longitudinal and transverse $P$-wave components. In isospin-asymmetric matter, neutron–proton Fermi-momentum splitting restricts the simultaneous low-energy contribution of the two species and can terminate the $np$ running at finite threshold scales. Our calculations are intended as controlled one-loop RG illustrations rather than as quantitative nuclear-matter calculations. We show how the Fermi-surface geometry and composition can change the ordering of competing pairing instabilities.
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Nuclear Theory

Neutron Stars consistent Equations of State with Phase Transitions and their Impact in Heavy Ion Collision Observables

D. E. Lluis González, J. Steinheimer and M. Bleicher

We explore the impact of different equations of state (EoS) on heavy ion collision observables using a Chiral Mean Field (CMF) framework constrained by astrophysical and lattice QCD inputs. The investigated family of EoS simultaneously reproduce neutron stars with masses above two solar masses and exhibit a first order phase transition around two times the nuclear saturation density. This is achieved by varying the relative vector and scalar couplings of ${\Delta}$ resonances with the scalar ${\sigma}$ and vector ${\omega}$ fields with respect to nucleons. These EoS are compared to the QCD trace anomaly at finite temperature. We implement both, the default CMF EoS and the modified EoS featuring a phase transition into the UrQMD transport model to study the effects of the phase transition on a qualitative and quantitative level. In particular Au+Au collisions at beam energies of 0.5-3 GeV, the GSI/FAIR energy range of the HADES and CBM experiments, shows visible sensitivity on the EoS. Transverse momentum distributions for protons, the directed flow ($v_1$) and its slope near mid-rapidity for ${\pi}^+$ as well as the $K^+/{\pi}^+$ ratio is analyzed. Clear differences emerge between the results obtained with the default CMF EoS, the modified EoS, and the cascade mode, particularly the slope of $v_1$ of the pions and in strangeness production. These findings demonstrate the sensitivity of heavy ion observables to the nuclear EoS and highlight potential experimental signatures of a phase transition.
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Nuclear Theory

Extension of the dispersive optical model to improve the description of high-momentum components

R. A. Ramon, M. C. Atkinson and W. H. Dickhoff

An improved treatment of high-momentum components in nuclei is introduced in the framework of the dispersive optical model (DOM). The well-established feature that the peak of the spectral function appears at higher excitation energy in the $A$-1 system with increasing momentum has so far not been successfully accounted for in the DOM. To achieve this feature, it is necessary to abandon the factorization of energy dependence and geometry of the DOM self-energy. The volume absorption below the Fermi energy has thus been represented by a decreasing radius at larger missing energy implying that a numerical treatment of the dispersion relations is necessitated. Earlier DOM results for ${}^{48}$Ca are also improved with this approach, demonstrating that a small neutron skin can still be accompanied by protons having a larger high-momentum tail than neutrons.
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Saturday 15 August

Nuclear Theory

General Lindblad equation for quarkonium evolution in a quark-gluon plasma

Aoumeur Daddi Hammou, Jean-Paul Blaizot, Pol Bernard Gossiaux et al. (+1 more)

Accurate modelling and understanding of quarkonium production in ultrarelativistic heavy ion collisions requires a formalism that preserves the quantum properties of microscopic $\bar{Q}Q$ systems while treating the interaction of such pairs with the quark-gluon plasma (QGP). The open quantum system approach has recently emerged as one of the most fruitful schemes to meet such requirements. However, the quantum master equations obtained so far in this context are derived assuming a strict ordering between the QGP temperature $T$ and the $\bar{Q}Q$ energy gaps ($\Delta E$) of the quarkonia bound states. This limits their predictive power since, as the QGP expands and cools down, the system traverse all regimes between the quantum Brownian motion (QBM) regime for $T\gtrsim \Delta E$ to the quantum optical (QO) regime for $\Delta E\gtrsim T$. In this paper, we derive and present a more general non-abelian quantum master equation of the Lindblad type, which does not suffer from these limitations and thus allows to faithfully describe the quantum evolution of the $Q\bar{Q}$ pairs during the whole QGP-evolution. We also provide some illustration of the key quantities governing this equation.
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All authors Aoumeur Daddi Hammou, Jean-Paul Blaizot, Pol Bernard Gossiaux, Thierry Gousset

Nuclear Theory · Cross-listed from hep-ph

Spin-dependent polarizabilities of heavy vector mesons

Hao Dang, Liang-Zhen Wen, Yan-Ke Chen et al. (+1 more)

We investigate the spin-dependent electromagnetic polarizabilities of the heavy vector mesons \(D^*\) and \(B^*\) in heavy meson chiral perturbation theory up to \(\mathcal O(p^3)\). Using a twelve-element tensor basis for the real-photon Compton scattering on a spin-1 target, we determine two scalar, four vector and six tensor polarizabilities. We take the charm- and bottom-sector axial couplings from the measured \(D^*\) width and lattice-QCD calculations, respectively, and estimate the magnetic couplings in the nonrelativistic constituent-quark model. In the charm sector, the proximity of the charged \(D\pi\) thresholds generates strongly nonanalytic \(P\phi\)-loop contributions, producing large real contributions to several \(\bar D^{*0}\) polarizabilities and sizable imaginary parts for \(D^{*-}\), whose charged \(D\pi\) channel is open. The \(E1E1\)-type polarizabilities are enhanced much more strongly than their \(M1M1\)-type counterparts, consistent with the velocity suppression of the pion-cloud magnetic coupling. No analogous enhancement occurs for \(B^*\): the Born terms govern the magnetic polarizabilities, and the anomaly poles dominate the vector polarizabilities that receive no Born contribution. These results resolve the spin dependence of the \(D\pi\) threshold effect and provide benchmarks for future lattice-QCD studies.
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All authors Hao Dang, Liang-Zhen Wen, Yan-Ke Chen, Shi-Lin Zhu

Nuclear Theory

Raubold-Lynch construction of the phase space in hypertriton three-body mesonic decay

Emile Meoto

A Monte Carlo construction is presented for the three-body mesonic decay phase space of the hypertriton. This is accomplished using the Raubold-Lynch sequential two-body decay algorithm. The method factorises this three-body decay into successive two-body decays through a virtual intermediate subsystem, whose invariant mass is sampled over the full kinematically allowed region. Exact relativistic two-body kinematics and Lorentz transformations are employed to construct complete four-momenta for all decay products. The construction is applied to both charged- and neutral-pion decay channels, yielding events that reproduce the Lorentz-invariant three-body phase-space measure. The resulting momentum spectra, pairwise momentum correlations, opening-angle distributions, and Dalitz plots furnish a complete kinematic characterisation of both decay modes. The neutral-pion channel exhibits a larger available three-body energy and correspondingly broader kinematic limits. The unweighted events generated provide a kinematic baseline that can subsequently be weighted event by event with a weak-decay matrix element, for computing decay rates and other observables. For the neutral-pion channel, where no experimental data currently exists, the Lorentz-invariant phase-space constitutes a useful baseline for predictions.
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Nuclear Theory · Cross-listed from nucl-ex

Best Reaction Target To Determine Proton Distribution Radii of Atomic Nuclei

Jun-Yao Xu, Bao-Hua Sun, Isao Tanihata et al. (+29 more)

We found that a heavy target such as Pb is most suitable for determining the proton distribution radii of unstable nuclei through charge-changing cross-section ($\sigma_\text{cc}$) measurements. As a heavy ion probe, low-$Z$ targets are routinely used to determine nucleon distribution radii of unstable isotopes. This approach has recently been extended to study proton distribution radii from $\sigma_\text{cc}$ measurements. However, empirical scaling factors have to be introduced to apply the Glauber models. In the present work, we systematically investigated the scaling factor using 39 new $\sigma_\text{cc}$ data of 18 $p$-shell nuclei on hydrogen, carbon, silver, and lead targets at around 240 MeV/nucleon. Together with the existing data, we reveal a universal dependence of the scaling factor on both the masses of target nuclei and the separation energies of projectile nuclei. The scaling factors decrease with increasing target-nucleus mass and converge to 1 for the highest-$Z$ target, making the scaling unnecessary. We conclude that instead of a low-$Z$ target, employing a heavy target such as Pb in $\sigma_\text{cc}$ measurements is the best option to determine the proton distribution radii of unstable nuclei.
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All authors Jun-Yao Xu, Bao-Hua Sun, Isao Tanihata, Satoru Terashima, Jian-Wei Zhao, Ji-Chao Zhang, Ge Guo, Shi-Tao Wang, Lei Shen, Jun Su, Xiao-Dong Xu, Andrej Prochazka, Guang-Shuai Li, Xiu-Lin Wei, Chang-Jian Wang, Feng Wang, Meng Wang, Jing Wang, Liu-Chun He, Chuan-Ye Liu, Wen-Jian Lin, Wei-Ping Lin, Zhong Liu, Pei-Pei Ren, Yu Zhang, Mei-Xue Zhang, Ya-Zhou Sun, Zhi-Yu Sun, Chen-Gui Lu, Xue-Heng Zhang, Jin-Rong Liu, Tian-Yu Wu

Friday 14 August

Nuclear Theory · Cross-listed from hep-ph

Radiative corrections to neutron $\beta$ decay with explicit $\Delta (1232)$ degrees of freedom

Lemonia Gialidi, Emanuele Mereghetti and Jordy de Vries

We study electromagnetic radiative corrections to neutron $\beta$ decay within chiral perturbation theory extended to include the $\Delta(1232)$ resonance as an explicit degree of freedom. Building on a previous analysis performed in the $\Delta$-less theory, we identify and compute additional loop contributions with intermediate $\Delta$ states at leading and next-to-leading order in the small-scale expansion, and match the results to the pionless effective field theory. We find that the convergence of the chiral expansion significantly improved in the $\Delta$-full calculation. The electromagnetic shift in the axial coupling is reduced by $25\%$ compared to the $\Delta$-less result. The correction remains at the percent level and is phenomenologically significant for the comparison between experimental extractions and lattice-QCD determinations of the nucleon axial charge. We also obtain a new $\Delta$-induced contribution to the weak magnetism term, which is an order of magnitude smaller than the pion-loop result and negligible for upcoming experiments.
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Nuclear Theory · Cross-listed from hep-ph

Energy Correlators in $V + X$ as a Benchmark Observable for Precision QCD

Terry Generet, Kyle Lee, Ian Moult et al. (+2 more)

We propose projected energy correlators measured on the recoiling QCD radiation of a $Z/\gamma$ as a benchmark observable for precision QCD at the LHC. Using the $Z/\gamma$ as a hard scale prevents the need for a jet algorithm, simplifying both the perturbative and non-perturbative corrections. We develop a framework to combine state-of-the-art fixed-order amplitudes, high order resummation, and universal non-perturbative matrix elements. Our approach is based on numerically computed inclusive hard functions, allowing flexibility in the process and the inclusion of realistic experimental cuts. We perform detailed numerical studies of the projected energy correlators at next-to-leading order + next-to-next-to-leading logarithm (NLO+NNLL) to verify the stability of our setup. We present numerical results at NLO+NNLL, which are the first complete matched predictions for energy correlators at the LHC at this order. We discuss the prospects for extensions to higher orders, outlining a path to NNLO calculations of energy correlators at the LHC.
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All authors Terry Generet, Kyle Lee, Ian Moult, Rene Poncelet, Xiaoyuan Zhang