Nuclear Theory·nucl-th

Thursday·March 26, 2026

17 papers—6 primary·11 cross-listed

01
Equation of state and cumulants of proton multiplicity in equilibrium near critical point from Pade estimates
Gokce Basar🇺🇸 · Maneesha Pradeep🇮🇳 · Mikhail Stephanov🇺🇸
The fluctuations of proton multiplicity in heavy-ion collisions are the key observables in the search for the QCD critical point. In this work we present an approach to constraining the cumulants of proton number based on the analytical properties of the QCD equation of state in the vicinity of the critical point. We show that, under the assumption of local equilibrium, the features of the collision energy dependence, such as the peaks and the dips of the cumulants, are significantly constrained by the data on the Lee-Yang singularity structure available via Pade resummation of the lattice QCD data. Furthermore, we identify four topologically distinct scenarios, all within the uncertainty range of the Pade estimates for the non-universal mapping parameters, classified based on the location of the critical point and the slope of the chiral crossover curve with respect to the freeze-out curve. These different scenarios result in qualitatively different critical signatures, especially for the third factorial cumulant and thus could be potentially discriminated using the experimental data.
nucl-th5 citations
02
The Effects of Multi- $Λ$ Hyperons on Collective Modes in Nuclei
Bahruz Suleymanli🇹🇷 · Kutsal Bozkurt🇹🇷 · Elias Khan🇫🇷 · Haşim Güven🇫🇷 · Jerome Margueron🇺🇸
The dynamical influence of $Λ$ hyperons on the excited-state properties of closed-shell multi- $Λ$ Ca, Ni, Sn and Pb hypernuclei is investigated using the self-consistent Hartree-Fock + Random Phase Approximation in coordinate space. The strength distributions for the isoscalar monopole, isovector dipole, and isoscalar quadrupole modes are calculated, revealing a systematic upward energy shift with increasing $Λ$ hyperon number $- S$ . The scaling behavior of the computed centroid energies $m_{1} / m_{- 1}$ with respect to both the mass and hyperon number is determined. The nuclear incompressibility modulus $K_{A}$ is found to increase monotonically with $- S$ . The largest value is found in the $_{50Λ}^{258}$ Pb hypernucleus, reaching $K_{A} = 322$ MeV. Calculations in uniform hypernuclear matter confirm that this stiffening is a bulk effect driven by both the $N Λ$ and $ΛΛ$ interactions. Analysis of the transition densities for states with maximal collective coherence indicates that the dynamical effect of $Λ$ hyperons is predominantly in phase with the protons, especially in the case of the isovector E1 modes.
nucl-thPRC(2026)·0 citations
03
Deep learning approaches to extract nuclear deformation parameters from initial-state information in heavy-ion collisions
Jun-Qi Tao🇨🇳 · Yang Liu🇨🇳 · Yu Sha🇨🇳 · Xiang Fan🇨🇳 · Yan-Sheng Tu🇨🇳 · Kai Zhou🇨🇳 · Hua Zheng🇨🇳 · Ben-Wei Zhang🇨🇳
The deformation of heavy nuclei leaves characteristic imprints on the initial conditions of relativistic heavy-ion collisions. However, event-by-event fluctuations make the quantitative extraction of this information challenging. This study examines the identifiability of the quadrupole ( $β_{2}$ ) and hexadecapole ( $β_{4}$ ) deformation parameters from nucleon configurations sampled from a deformed Woods-Saxon distribution commonly used in initial-state modeling of heavy-ion collisions. As a baseline, we first establish an upper bound on the "intrinsic identifiability" of deformation information at the most microscopic level by constructing permutation-invariant point-cloud networks under controlled multi-event grouping. We then extend the analysis to the more realistic initial entropy-density profiles generated by the TRENTo model, where both standard regression and simulation-based inference (SBI) with conditional normalizing flows are employed to reconstruct the deformation parameters from ensembles of event images supplemented with global attributes. Multi-event averaging is found to be essential in this setting for suppressing stochastic fluctuations and revealing the underlying deformation information. While standard regression efficiently captures the central trends of deformation through point estimates, SBI provides calibrated posterior distributions, offering a more complete and robust characterization of uncertainty. Collectively, our results demonstrate that deformation information is effectively encoded in the initial state and becomes increasingly identifiable with sufficient ensemble averaging, laying a solid foundation for future extensions toward more complete dynamical modeling and final-state observables.
nucl-th0 citations
04
Assessing continuum channel importance in continuum-discretized coupled-channels via dynamic polarization potential decomposition
Jin Lei · Hao Liu
A recurring question in continuum-discretized coupled-channels (CDCC) calculations is which continuum channels carry the breakup coupling, both to interpret the reaction and to decide which channels a model space can safely omit. The standard answer is bin deletion: remove a channel, re-solve the coupled equations, and read the change in the elastic $S$ -matrix. We show that this cannot isolate an individual channel's contribution. Deleting a channel forces the surviving model space to reorganize, the neighboring bins rerouting through the off-diagonal Green's function, so the recorded change mixes the channel's own effect with the readjustment of all the others. Working instead from the channel-resolved Feshbach dynamic polarization potential (DPP), whose full-coupling Green's function is a fixed reference shared by every channel, we define an exclusion that removes one channel while holding that reference fixed, returning its contribution to the intact system. The two operations disagree on which continuum bins matter most, for $d$ + $^{58}$ Ni at 21.6~MeV even reversing their order of importance. The DPP further separates each channel's action into a direct path, virtual excitation and return, and a bridge path, relayed through neighboring bins, a split deletion cannot make; it shows the bins act on the elastic channel mainly as bridges, robustly across angular momentum, and that it is this bridge coupling that reorganizes under deletion. A deletion-based channel importance is therefore best read as the truncated calculation's sensitivity to a channel's removal, not as the channel's intrinsic coupling strength.
nucl-thquant-phPRC(2026)·0 citations
05
Qcombo: A Python Package for Automated Commutator Calculations of Quantum Many-Body Operators
L. H. Chen · Y. Li · H. Hergert · J. M. Yao
qcombo is a Python package for the symbolic evaluation of commutators between general quantum many-body operators expressed in normal-ordered form using the generalized Wick theorem. The package provides an automated and systematic framework for generating the corresponding algebraic expressions, significantly reducing the risk of human error in lengthy and complex analytical derivations. It is designed to assist the development and implementation of modern many-body methods in nuclear physics, quantum chemistry, and related fields. The functionality and workflow of the package are demonstrated through an application to the in-medium similarity renormalization group (IMSRG) method, which has been widely used for nuclear ab initio calculations. As a representative example, qcombo is employed to automatically generate the complete set of multi-reference IMSRG flow equations with operators truncated at the normal-ordered three-body level.
nucl-thcond-mat.str-el2 citations
06
Many-body perturbation theory for the nuclear equation of state up to fifth order
C. Drischler🇺🇸 · K. S. McElvain🇺🇸 · P. Arthuis🇫🇷
We present an automated, GPU-accelerated framework for many-body perturbation theory (MBPT) calculations of the zero-temperature nuclear equation of state (EOS) based on chiral nucleon-nucleon (NN) and three-nucleon (3N) interactions. Automated diagram generation and evaluation enable the computation of all diagrams up to fifth order in the MBPT expansion at the normal-ordered two-body level in infinite matter, with residual three-body contributions explicitly included up to third order. Multi-GPU acceleration of 3N normal ordering, a novel Monte Carlo integrator (called PVegas), and further advances in high-performance computing enable us to evaluate all 840 fifth-order diagrams with controlled numerical uncertainties. We investigate the MBPT convergence up to fifth order in pure neutron matter (PNM) and symmetric nuclear matter (SNM) for two sets of chiral interactions, study neutron star matter, and present fourth-order results for asymmetric matter including normal-ordered 3N forces. The framework enables systematic MBPT studies with harder interactions and benchmarks against nonperturbative methods. It can be further extended to finite-temperature EOS calculations and to improved uncertainty quantification using emulation and resummation techniques.
nucl-thhep-phnucl-ex6 citations
07
Radiative corrections to two-neutrino double-beta decay
Jordy de Vries🇳🇱 · Emanuele Mereghetti🇺🇸 · Saad el Morabit🇳🇱 · Stefan Sandner🇺🇸
We use heavy-nucleus effective field theory to compute radiative corrections to two-neutrino double- $β$ decay ( $2 ν β β$ ). Our main result is the first derivation of a universal radiative-correction factor for double-weak decays -- the analogue of the Sirlin function in single- $β$ decay -- independent of nuclear matrix elements and excitation energies. This "double-weak Sirlin function" depends on the individual electron energies as well as their relative angle and differs significantly from the approximation obtained by summing two single- $β$ decay Sirlin functions. In addition, we calculate the nuclear-structure-dependent component of the radiative corrections and find that they can still be neglected at current experimental sensitivities. On the other hand, the double-weak Sirlin function induces distortions of the electron energies and angular spectra that are comparable in size to the leading nuclear-structure corrections parametrized by the ratio of nuclear matrix elements, $ξ_{31}$ . Our results indicate that extractions of nuclear structure information and tests of the Standard Model from high-precision $2 ν β β$ measurements must include double-weak radiative corrections, implying that recent extractions of $ξ_{31}$ should be revisited.
↳ hep-phnucl-exnucl-thPRL(2026)·0 citations
08
A Breath of Fresh Air for Molière: Detecting Molière Scattering using Jet Substructure Observables in Oxygen Collisions
Arjun Srinivasan Kudinoor🇺🇸 · Arthur Yi-Ting Lin🇺🇸 · Daniel Pablos🇪🇸 · Krishna Rajagopal🇺🇸
Ultra-relativistic oxygen-oxygen (OO) collisions are a promising arena in which to probe rare, large-angle, high momentum-transfer $2 \to 2$ Molière scatterings between energetic jet partons and quasiparticles in quark-gluon plasma (QGP). As a jet propagates through the droplet of QGP formed in the same collision, its constituents lose energy to and excite wakes in the medium, and may scatter off quark- and gluon-like quasiparticles in QGP. Using the hybrid strong/weak coupling model, we show that including Molière scatterings between jet partons and medium quasiparticles is essential to reproduce recent CMS measurements of charged-particle suppression in OO collisions with this model. We then present the first theoretical study of how jet-medium interactions modify the internal structure of jets in OO collisions. We find that Molière scatterings broaden the Soft Drop splitting angle $R_{g}$ , enhancing the population of $R = 0.4$ and $R = 0.8$ jets with $R_{g} ≳ 0.2$ in OO collisions relative to pp collisions. Energy-energy correlators (EECs) provide a complementary probe, exhibiting enhanced large-angle correlations within jets due to jet-induced wakes and Molière scattering. In both cases, we propose an experimental measurement where the relevant OO/pp ratio can, if enhanced above unity in future data as in our calculations, be a distinctive, model-independent, detection of hard scattering off QGP quasiparticles. We furthermore use our calculations of EECs to show how the angular scale corresponding to the deflection of jet or medium partons by Molière scattering is imprinted in the EEC for jets with radius $R_{jet} \sim 0.8$ in OO collisions. These results demonstrate that jet substructure measurements in OO collisions are promising avenues to probe the quasiparticles that emerge at short distances within an otherwise strongly coupled medium.
↳ hep-phhep-thnucl-exnucl-th5 citations
09
Information-Geometric Quantum Process Tomography in Unital Open Single-Qubit Dynamics
T. Koide🇧🇷 · A. van de Venn🇪🇪
We derive an exact information-geometric inequality valid for both Markovian and non-Markovian mixed-state dynamics. This inequality saturates into a strict equality for single qubits because they belong to the quantum exponential family. This identity enables a non-iterative linear regression approach to continuous-time quantum process tomography, which, provided the full-rank condition is satisfied, yields a unique global solution and avoids local minima traps typical of standard non-linear optimization. Furthermore, as the formulation is inherently unconstrained, negative dissipation rates provide direct evidence of non-Markovianity. Numerical simulations of the unital diagonal Bloch generator derived from the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equation demonstrate the validity of this geometric estimator and highlight the necessity of error mitigation near the pure-state boundary where the inverse metric becomes singular.
↳ quant-phcond-mat.stat-mechhep-thnucl-thPLA(2026)·0 citations
10
Semi-inclusive deep-inelastic scattering on a polarized spin-1 target. I. Cross section and spin observables
W. Cosyn🇺🇸 · C. Weiss🇺🇸
We develop the theoretical framework for semi-inclusive deep-inelastic scattering on a polarized spin-1 target and apply it to scattering on the polarized deuteron with spectator nucleon tagging. In Part I (this article) we present the general form of the semi-inclusive cross section and polarization observables for the spin-1 target. A relativistically covariant formulation in terms of 4-vectors and invariant polarization parameters is employed. The target polarization is described by a spin density matrix with vector and tensor polarization. The spin and azimuthal angle dependence of the semi-inclusive cross section is derived and parametrized in terms of invariant structure functions. To validate the result, the structure functions are expressed as photon-target helicity amplitudes with known symmetry properties. The expressions presented here are kinematic (no assumptions about particle production dynamics) and valid in all regions of the deep-inelastic final state (current and target fragmentation regions). In Part II (following article), we consider deep-inelastic scattering on the polarized deuteron with spectator nucleon tagging as a special case of target fragmentation. The semi-inclusive structure functions are computed by separating nuclear and hadronic structure, and the polarization observables are explored as functions of the tagged nucleon momentum.
↳ hep-phnucl-exnucl-thPRC(2026)·2 citations
11
Semi-inclusive deep-inelastic scattering on a polarized spin-1 target. II. Deuteron and spectator nucleon tagging
W. Cosyn🇺🇸 · C. Weiss🇺🇸
We develop the theoretical framework for semi-inclusive deep-inelastic scattering on a polarized spin-1 target and apply it to scattering on the polarized deuteron with spectator nucleon tagging. In Part I (previous article) we present the general form of the semi-inclusive cross section and polarization observables for the spin-1 target. In Part II (this article) we consider deep-inelastic scattering on the polarized deuteron with spectator nucleon tagging as a special case of target fragmentation. Methods of light-front quantization are employed to separate nuclear and hadronic structure in the high-energy process and achieve a composite description. The light-front wave function of the polarized deuteron is obtained from a rotationally covariant 3-dimensional wave function in the center-of-mass frame of the proton-neutron system. The tagged structure functions are computed in the impulse approximation. The momentum and spin distribution of the active nucleon are controlled by the deuteron polarization and the detected spectator momentum ( $D / S$ wave ratio). The cross section and spin asymmetries are evaluated for general deuteron polarization (vector and tensor, longitudinal and transverse) as functions of the spectator momentum. Tensor-polarized spin asymmetries of order unity are achieved for spectator momenta $\sim$ 300 MeV, which select configurations with large $D$ -wave. Sum rules for the tagged spin structure functions are derived. The results can be used for simulations of spectator tagging in future polarized fixed-target experiments (Jefferson Lab) or at the Electron-Ion Collider.
↳ hep-phnucl-exnucl-thPRC(2026)·2 citations
12
Meson mixing effects on the speed of sound in isospin-imbalanced matter
Alejandro Ayala · Bruno S. Lopes · Ricardo L. S. Farias · Luis C. Parra
We explore isospin imbalanced strongly interacting matter within the two-flavor Linear Sigma Model with quarks, an effective model for low-energy QCD. At one loop order, including quark, pion, and sigma fluctuations while respecting chiral symmetry, we find that the formation of an isospin condensate necessarily gives rise to a Goldstone mode. This mode enforces a nontrivial relation between the chiral and isospin condensates through the mixing of charged pions and the sigma field in the condensed phase. From the resulting thermodynamic potential, we compute the speed of sound and observe a pronounced peak as a function of the isospin chemical potential. Although the peak of the speed of sound may be described at tree-level and including only quarks in the analysis, meson dynamics introduces further constraints that influence the position and width of the peak which making it to align well with lattice QCD simulations. Therefore we identify that the shape and position of the peak is a consequence of the Goldstone mode dynamics and of the associated charged pion sigma mixing.
↳ hep-phhep-lathep-thnucl-thPoS(2026)·0 citations
13
Impact of muons on the bulk viscosity of neutron star matter metamodels
José Luis Hernández🇪🇸 · Cristina Manuel🇪🇸 · Laura Tolos🇪🇸
Recent studies invoke a unified description of different neutron star observables using metamodels, which parametrize the Equation of State (EoS) of neutron star matter close to nuclear saturation density in terms of few nuclear parameters. In this light, the bulk viscosity in the neutrino-transparent regime of dense nuclear matter composed of neutrons, protons and electrons has been recently shown to be mostly sensitive to the value of the nuclear symmetry energy. As muons are also present at densities around nuclear saturation, we further analyse in this manuscript their impact on this transport coefficient as a function of the slope $L$ of the symmetry energy. We find that muons introduce both relevant qualitative and quantitative effects in the bulk viscous dissipation. Increasing $L$ by a factor two has an effect of several orders of magnitude on the (frequency-independent) bulk viscosity. We also find that for all values of $L$ the frequency-dependent bulk viscosity presents a double peak structure for some values of the density, absent without muons. This also represents changes in orders of magnitude of the viscosity in narrow windows of densities that could be attainable in a neutron star for enough high values of $L$ . We present a systematic numerical analysis of both second-order transport coefficients, frequency-dependent bulk viscosity, and damping times of density oscillations as a function of the density and the slope, and find when these could be relevant for the dynamics of the merger of neutrons stars.
↳ hep-phastro-ph.HEnucl-th1 citation
14
Local Thermalization of SU(2) Lattice Gauge Fields on Quantum Computers
Jiunn-Wei Chen🇹🇼 · Yu-Ting Chen🇹🇼 · Ghanashyam Meher🇹🇼 · Berndt Müller🇺🇸 · Andreas Schäfer🇩🇪 · Xiaojun Yao🇺🇸
We simulate the local thermalization dynamics for minimally truncated SU(2) pure gauge theory on linear plaquette chains with up to 151 plaquettes using IBM quantum computers. We study the time dependence of the entanglement spectrum, Rényi-2 entropy and anti-flatness on small subsystems. The quantum hardware results obtained after error mitigation agree with extrapolated classical simulator results for chains consisting of up to 101 plaquettes. Our results demonstrate the feasibility of local thermalization studies for chaotic quantum systems, such as nonabelian lattice gauge theories, on current noisy quantum computing platforms.
↳ hep-lathep-phnucl-thquant-ph10 citations
15
Precision Tests of Isospin Symmetry through Coulomb excitation of A = 62 Nuclei
K. Wimmer🇩🇪 · T. Hüyük🇪🇸 · S. M. Lenzi🇮🇹 · A. Poves🇪🇸 · F. Browne🇯🇵 · P. Doornenbal🇯🇵 · T. Koiwai🇯🇵 · T. Arici🇩🇪 · M. A.~Bentley🇬🇧 · M. L.~Cortés🇮🇹 · T. Furumoto🇯🇵 · N. Imai🇯🇵 and 15 other authors
Isospin symmetry in the $A = 62$ mass system was investigated through Coulomb excitation reactions at the RIKEN Radioactive Isotope Beam Factory. Beams of $^{62}$ Zn, $^{62}$ Ga, and $^{62}$ Ge were studied using the BigRIPS-ZeroDegree-DALI2 $^{+}$ setup under identical experimental conditions, allowing for cancellation of systematic uncertainties. Inelastic scattering cross sections measured with two different targets were used to extract nuclear deformation lengths and $E 2$ matrix elements. The isospin symmetry of the $A = 62$ system was rigorously tested by examining the linearity of the proton matrix elements within the triplet with high precision. The observed linear relationship between the reduced proton matrix elements for the three nuclei holds within experimental uncertainties, providing a stringent test of isospin symmetry. This experiment provides the most accurate test, to date, of isospin symmetry rules using transition matrix elements. These results were interpreted using large-scale shell-model calculations, offering valuable insights into isospin symmetry behavior in this region of the nuclear chart.
↳ nucl-exnucl-thPLB(2026)·1 citation
16
The dipole strength distribution of $^{8}$ He and decay characteristics
C. Lehr🇩🇪 · T. Aumann · M. Duer🇩🇪 · A. T. Saito🇯🇵 · T. Nakamura🇯🇵 · N. L. Achouri🇫🇷 · D. Ahn🇯🇵 · H. Baba🇯🇵 · S. Bacca🇩🇪 · C. A. Bertulani🇺🇸 · M. Böhmer🇩🇪 · F. Bonaiti🇩🇪 and 82 other authors
The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus $^{8}$ He is the most neutron-rich bound nucleus with a mass-to-charge ratio of $A / Z = 4$ . We measure the dipole response of $^{8}$ He, including for the first time the four-neutron decay channel. A total dipole strength of $\sum B (E 1) (E^{*} < 15$ ~MeV $) = 0.95 (16) e^{2}$ fm $^{2}$ and a dipole polarizability of $α_{D} = 0.61 (1)$ ~fm $^{3}$ are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the $4 n$ decay threshold, by two-neutron emission, pointing to a $^{6}$ He $+ 2 n$ structure of the excited dipole mode. No indication was found for a $4 n$ final-state correlation, while pronounced $nn$ and $^{6}$ He- $n$ final-state correlations are apparent.
↳ nucl-exnucl-thPRL(2026)·2 citations
17
Effects of the initial-state geometry on D-meson production in pp and pPb collisions
R. Terra🇧🇷 · A. V. Giannini🇵🇹 · F. S. Navarra🇧🇷
Going from lower to higher multiplicity events in proton-proton and proton-lead collisions, the data show a stronger than linear growth of the D-meson normalized yields. In this contribution we try to understand this behavior using a Monte Carlo event generator which implements the $k_{T}$ -factorization formalism. We use different spatial distribution of matter in the proton and in the lead nucleus at the initial stage of these collisions. We find that, with all the tested spatial distributions, the model reproduces well the behavior seen in the data. We conclude that this observable is not appropriate for a detailed study of the spatial distribution of matter in the proton.
↳ hep-phnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE