Nuclear Theory·nucl-th

Friday·June 12, 2026

13 papers—6 primary·7 cross-listed

01
Analytic calculator for determination of $γ$ -ray angular distribution coefficients and tensors in aligned and partially-aligned nuclei
A.M. Hurst · D.A. Matters · T. Kawano
A program has been developed to calculate a complete set of $γ$ -ray angular distribution coefficients and statistical tensors in maximally- and partially-aligned nuclei. For practical nuclear structure and reaction purposes, there is no imposed constraint on any arguments that are likely to arise in the determination of these quantities. The program can also be used as a stand-alone vector-coupling calculator for the exact evaluation of Clebsch-Gordan and Racah coefficients, the closely-related Wigner 3- $j$ , 6- $j$ , and 9- $j$ symbols, as well as Gaunt coefficients. These quantities, which frequently arise in quantum mechanical applications involving angular momentum coupling and recoupling schemes, provide the underlying machinery in angular distribution calculations.
nucl-th0 citations
02
Efficient emulation of nuclear ground states with neural-network variational Monte Carlo and eigenvector continuation
Mao Li · Yilong Yang · Pengwei Zhao
An efficient emulator for \emph{ab initio} calculations of nuclear ground-state properties is developed by integrating the neural-network variational Monte Carlo framework, FeynmanNet, with the eigenvector continuation. It enables the calculation of observables for different Hamiltonians with minimal computational cost, while delivering ground-state energies with errors below $0.5%$ compared to the full FeynmanNet results. With this emulator, the ground-state energies and charge radii of $^{16} O$ , $^{15} O$ , $^{14} O$ , $^{15} N$ , and $^{14} C$ are computed using a nuclear Hamiltonian derived from the leading-order pionless effective field theory, with a large number of different values of low-energy constants (LECs). Then, we perform a global sensitivity analysis of the ground-state energies, charge radii, separation energies of selected nuclei for the three LECs in the Hamiltonian, to identify how each LEC contributes to the variances of these observables. It shows that the two-body LEC in the $^{3} S_{1}$ channel is the most influential LEC governing these nuclear bulk properties. Finally, the correlations among the ground-state energies of $^{4}$ He, $^{12}$ C, and $^{16}$ O are investigated by varying the LECs in the Hamiltonian. The analysis reveals that the experimental ground-state energies of $^{12}$ C and $^{16}$ O cannot be reproduced simultaneously by varying the LECs in the leading-order pionless Hamiltonian. This suggests that additional ingredients in the leading-order Hamiltonian are required to improve its description of light nuclei. The present work establishes an efficient framework for global sensitivity analysis and uncertainty quantification in the quantum Monte Carlo calculations for light and medium-mass nuclei.
nucl-thPRC(2026)·2 citations
03
The leading nuclear-structure electrostatic correction in arbitrary $β$ decays
Daniel Benatar🇮🇱 · Ayala Glick-Magid🇮🇱 · Doron Gazit🇮🇱
We develop a systematic theoretical framework to improve theoretical predictions for nuclear $β$ decays of arbitrary angular momentum $J$ , leading to a model-independent nuclear-structure electrostatic correction to the Coulomb interaction between the emitted lepton and the nuclear charge distribution, useful for ongoing and future precision searches for physics beyond the Standard Model. The formalism is based on nuclear matrix elements expanded in multipole operators, as commonly used in \emph{ab initio} calculations. First-order Coulomb corrections are derived from one-photon exchange preserving the full multipole and angular structure of the decay rate, and are subsequently expanded in the relevant small parameters of the nuclear problem, suppressing the leading nuclear structure correction to a few per-mills for medium mass nuclei with natural beta decay properties. We show that within this formalism, the leading Coulomb correction originates from three modifications of the original weak-only interaction: a modification of the nuclear charge form factor, which yields a correction similar to the known Fermi function, a shift of the momentum transfer within the lepton traces, and the same shift but inside the nuclear multipole operators. We additionally provide explicit results for allowed Gamow--Teller and unique first-forbidden transitions.
nucl-thhep-phnucl-ex1 citation
04
Hadron polarization and equation of state at FAIR/RHIC-BES energies
Dai-Neng Liu · Jan Steinheimer · Kai-Jia Sun🇨🇳 · Jin-Hui Chen🇨🇳 · Yu-Gang Ma🇨🇳 · Marcus Bleicher🇩🇪
The $Λ$ global polarization indicates that hot and dense matter created in non-central heavy-ion collisions carries large orbital angular momentum. However, the relation between hadronic polarization and the medium's collective rotation remains to be validated. Using the UrQMD transport model, we calculate the thermal vorticity-induced polarization of $Λ$ s in Ag+Ag and Au+Au collisions from $s_{NN} = 2.24$ - $7.7$ GeV and a range of centralities. Two different equations of state used in the UrQMD simulation are compared: one resembles a hadron resonance gas, while the other is based on the chiral mean field (CMF) model, providing a more realistic description of dense nuclear matter including a chiral transition that is consistent with lattice QCD expectations. The polarization is sensitive to the equation of state and a softer EoS leads to smaller values. In addition, we show that the $Λ$ polarization in the experimental acceptance and centrality selection does not decrease for even lower beam energies. Our results indicate that the process leading to the large vorticity is a result of the large shear in the baryon current created by its stopping.
nucl-th0 citations
05
Transport simulations with a constrained momentum-dependent Chiral Mean Field EoS at different iso-spin fractions
Jan Steinheimer🇩🇪 · Marcus Bleicher🇩🇪
We present a comparison of the UrQMD model using a chiral mean field EoS (CMF) with flow and pion production data in heavy ion collisions at low beam energies $E_{lab} = 0.2 - 2.0 A$ GeV and varying iso-spin fraction. The CMF model parameters are constrained by known properties of the high density equation of state of QCD at varying iso-spin fractions. This allows us to calculate the equation of state as well as nuclear interactions for different physical systems like neutron stars and heavy ion collisions in a consistent way. It is found that heavy ion reactions at the upcoming FAIR facility will only have marginal sensitivity on the iso-spin dependence of the high-density equation of state. At lower beam energies, comparing to FOPI, HADES and S $π$ rit data, the sensitivity is higher but the observed deviations and systematic uncertainties of the existing data are larger than the sensitivity to the symmetry energy.
nucl-th1 citation
06
Observable Dependence of Viscous Corrections in QGP: Heavy Quarks and Dileptons in Chapman--Enskog Theory
Lakshmi J. Naik · P. Parvathi · Nachiketa Sarkar · V. Sreekanth
We calculate, for the first time, heavy quark transport and thermal dilepton production from QGP using viscous correction up to second order in gradients. We use the form of viscous correction obtained from Chapman-Enskog like expansion of the Boltzmann transport equation in relaxation time approximation, and compare our results with that of Grad's 14-moment approximation. By employing the temperature and shear stress evolution profiles of QGP obtained from second-order causal relativistic viscous hydrodynamics, we study the heavy quark transport coefficients and thermal dilepton production from an evolving QGP. In the case of HQ transport, the CE corrections suppress the drag force substantially, induce a non-trivial momentum dependence in transverse momentum diffusion, and result in a comparatively less modification in longitudinal momentum diffusion. Whereas, for thermal dileptons, the CE corrections result in an enhanced early-time contribution which decreases and become converging to the first-order CE correction with the evolution of QGP, and remain well behaved compared to that of Grad's correction. Our results indicate that the modification of the observable due to viscous corrections is governed by the magnitude of the corrections as well as the interplay between their momentum dependence and momentum weighting of the transport and emission kernels. We demonstrate that the momentum structure of the various viscous corrections at the level of distribution function is not directly translated to the observables since the different observables are sensitive to distinct regions of momentum space.
nucl-thhep-ph0 citations
07
Constraining the Low- $p_{T}$ $η / π^{0}$ Ratio for Direct-Photon Analyses with Blast-Wave Fits to $π$ , $K$ , and $p$ Spectra
Klaus Reygers · Andreas Kirchner · Aleksas Mazeliauskas
We predict the $η / π^{0}$ ratio at low $p_{T}$ ( $p_{T} ≲ 3 GeV / c$ ) using the measured charged $K / π$ ratio and model input from a blast-wave framework with feeddown contributions. This approach can provide improved, data-constrained background estimates for direct-photon and dilepton measurements in heavy-ion collisions. In this approach, the explicit modeling of radial flow and hadronic feeddown enables an uncertainty estimate for the low- $p_{T}$ extrapolation of the $η / π^{0}$ ratio. Using central Pb-Pb collisions at $s_{N N} = 2.76$ TeV as an example, we find that the $η$ -related decay-photon uncertainty at $p_{T} \approx 1 GeV / c$ is of order 10\% of the expected direct-photon signal.
↳ nucl-exnucl-th0 citations
08
Analytic structure of the QCD phase diagram in the complex-temperature plane
Gokce Basar🇺🇸 · Vladimir V. Skokov🇺🇸
We study the analytic structure of the QCD phase diagram by treating temperature as a complex variable. The nearest Yang-Lee edge singularities in the complex $T$ plane bound the domain of analyticity of temperature-dependent thermodynamic observables and complement the more commonly studied singularities in the complex chemical-potential plane. Our analysis combines three complementary perspectives: universal critical scaling, a first-principles extraction from lattice-QCD data, and explicit illustrations in effective models. We illustrate the resulting structure in a random-matrix model and in a quark-meson model, where the singularity trajectories can be followed explicitly. At small real chemical potential, the leading complex-temperature singularity admits an analytic expansion in $μ^{2}$ , while near a critical point it crosses over to the universal Puiseux form dictated by Ising critical scaling. We show that the complex- $T$ and complex- $μ$ trajectories are controlled by the same scaling variables and mapping coefficients, so their comparison provides a stringent consistency test of critical-point searches and constrains the extent of the critical scaling regime. Finally, we analyze lattice-QCD data at $μ = 0$ using an iterated conformal-Pade approach and extract the continuum location of the nearest complex-temperature singularity. The result is consistent with the expectation that, at physical quark masses, the real part of the leading singularity lies between the chiral-limit transition temperature and the physical-mass chiral-susceptibility peak temperature, while its imaginary part remains nonzero.
↳ hep-thhep-latnucl-thPRD(2026)·0 citations
09
Accidental Symmetry in the Tavis-Cummings Model via the Schwinger Boson Representation
Plato Deliyannis🇺🇸 · Iman Marvian🇺🇸
The Jaynes-Cummings (JC) Hamiltonian is a paradigmatic model of light-matter interaction and, more generally, qubit-boson interactions, widely used across atomic, optical, and superconducting qubit platforms. In the multi-qubit setting, where n qubits are identically coupled to a single boson mode, this interaction is known as the Tavis-Cummings (TC) Hamiltonian. The structure of the TC model is usually understood in terms of two standard symmetries: permutation invariance of the qubits and a U(1) symmetry associated with conservation of the total excitation number. Here we identify an additional, independent "accidental" symmetry of the TC Hamiltonian and construct the corresponding conserved observable. We show that, for n>2 qubits, this symmetry imposes strong constraints on the realizable unitary transformations. These constraints persist in the presence of the global $J_{z}$ Hamiltonian, but are removed by adding $J_{z}^{2}$ , even though $J_{z}^{2}$ preserves both permutation invariance and the U(1) symmetry. Finally, we explain the origin of this previously unnoticed symmetry using Schwinger's boson representation of angular momentum. These restrictions have important implications for controllability of the TC system and for its applications to quantum computing, which are investigated further in a companion paper.
↳ quant-phcond-mat.mes-hallmath-phmath.MP+20 citations
10
Global Control with the Tavis-Cummings Interaction
Plato Deliyannis🇺🇸 · Iman Marvian🇺🇸
We study the controllability of a system of qubits under global control, where control pulses act identically on all qubits. Specifically, we consider a collection of qubits identically coupled to a single bosonic mode, or harmonic oscillator, via the Jaynes-Cummings interaction. This collective coupling, known as the Tavis-Cummings (TC) interaction, has been realized in several quantum computing platforms, including superconducting and atomic qubit systems. Although the qubits do not interact directly with one another, they can become entangled through their common coupling to the bosonic mode. We characterize the group of unitaries that can be implemented on the joint Hilbert space of the qubits and bosonic mode using the TC interaction together with a global $z$ field $J_{z}$ , corresponding to identical z rotations on all qubits. We show that for n>2 qubits the set of realizable unitaries is restricted by an "accidental" symmetry of the TC Hamiltonian, distinct from its "standard" U(1) and permutational symmetries. On the other hand, we find that the Hamiltonian $J_{z}^{2}$ breaks this accidental symmetry and, together with the TC interaction and $J_{z}$ , achieves semi-universality: it allows the implementation of arbitrary unitaries that respect permutational and U(1) symmetry, up to certain constraints on the center of the group. In a companion paper, we further analyze this remarkable accidental symmetry and show that it can be understood through Schwinger's bosonic model of angular momentum.
↳ quant-phcond-mat.mes-hallmath-phmath.MP+20 citations
11
Nucleon matrix elements of axial anomaly, axial currents and pseudoscalar currents in the QCD sum rule
Janardan Prasad Singh🇮🇳
We have analyzed one-nucleon matrix elements of current-current correlators; the currents consist of pseudoscalar octet, isovector and isoscalar currents, axial anomaly, and axial isovector and isoscalar currents. Using QCD sum rules, the coupling constants of nucleon with each of these currents have been expressed in terms of nucleon matrix elements of quark, gluon and quark-gluon composite operators and moments of parton distribution function. On the phenomenological side, contribution from the non-diagonal matrix elements of operators between nucleon and its excited states or continuum states have also been accounted for. For the pseudoscalar coupling constants of the nucleon two expressions have been obtained in which one of them consists of only moments of parton distribution function but yielding approximately same numerical result as the other one. Of particular interest is the nucleon matrix element of axial anomaly which has been largely ignored in the current literature.
↳ hep-phnucl-th0 citations
12
Transport coefficients of strongly interacting quark-gluon plasma including elastic and inelastic scattering within the dynamical quasiparticle model
Gaia Ingrosso🇩🇪 · Olga Soloveva🇩🇪 · Ilia Grishmanovskii🇩🇪 · Taesoo Song🇩🇪 · Elena Bratkovskaya🇩🇪
We study the impact of inelastic gluon-radiation and absorption processes on the transport coefficients of the quark-gluon plasma within the dynamical quasiparticle model (DQPM) in the temperature--baryon-chemical-potential plane $(T, μ_{B})$ . Extending the $2 \to 2$ baseline established in previous DQPM calculations, we include gluon-radiation $2 \to 3$ and the inverse gluon-absorption $3 \to 2$ scattering channels with massive partons and effective DQPM propagators and vertices. The corresponding momentum-dependent interaction rates and relaxation times are used to calculate the shear viscosity, bulk viscosity, electric conductivity, and baryon diffusion coefficient as functions of temperature $T$ and baryon chemical potential $μ_{B}$ . Within the relaxation time approximation, we find that $2 \leftrightarrow 3$ contributions systematically reduce all considered transport coefficients relative to the $2 \to 2$ only results, in accordance with the decrease of the relaxation times. In the thermal regime explored here, however, this reduction remains moderate, since the investigated inelastic rates stay below the $2 \to 2$ ones over the considered $(T, μ_{B})$ range. The inelastic channels become more relevant mainly for partonic scatterings at large momenta, which are thermally suppressed in the strongly interacting QGP. At $μ_{B} = 0$ , the resulting $η / s$ , $ζ / s$ , and $σ_{Q} / T$ are compatible with available lattice-QCD estimates within uncertainties. At finite $μ_{B}$ , our results provide predictions for the transport properties of QCD matter relevant for beam-energy-scan programs.
↳ hep-phnucl-th0 citations
13
Classification of Compact Stars via Machine Learning and Neural Network Models
D. Neraki🇬🇷 · G. Koufetidis🇬🇷 · I. Stergakis🇬🇷 · Th. Diakonidis🇬🇷 · Ch.C. Moustakidis🇬🇷
Recent advances in multimessenger astronomy, particularly through gravitational-wave observations of compact-object mergers, have significantly improved our understanding of dense matter. Nevertheless, the internal composition of compact stars remains uncertain. Depending on the underlying equation of state (EoS), these objects may be neutron stars composed primarily of nucleons, quark stars made of deconfined quark matter, or hybrid stars containing both hadronic and quark phases. More exotic constituents, such as hyperons, meson condensates, or dark matter, have also been proposed. In this work, we investigate whether the internal composition of compact stars can be inferred from observable quantities, including mass, radius, and tidal deformability. To address this problem, we employ machine-learning and deep-learning techniques trained on a larg dataset of EoSs describing both neutron stars and quark stars. From these EoSs, we generate the corresponding mass radius relations spanning a wide range of stellar configurations. The resulting dataset is used to train and evaluate classification models aimed at identifying the nature of compact objects from their macroscopic properties. Our results indicate that suitable combinations of observables can distinguish neutron stars from quark stars with very high accuracy. These findings demonstrate the potential of machine-learning approaches as tools for probing the composition of dense matter. However, further studies incorporating additional scenarios, including hybrid stars and other exotic forms of matter, are required to establish the robustness and general applicability of this methodology.
↳ astro-ph.HEastro-ph.IMastro-ph.SRgr-qc+10 citations

Affiliations

first authorsco-authorsvia INSPIRE