Nuclear Theory·nucl-th

Wednesday·July 29, 2026

16 papers—6 primary·10 cross-listed

01
[Submitted on 26 Jul 2026]
Prompt Fission Neutron Spectra of 233U(n, F), 235U(n, F), 239Pu(n, F) and 240Pu(n,F)
V.M. Maslov
The prompt fission neutron spectra of fuel and fertile nuclei are of key importance for the safety/efficiency of nuclear reactors, deployed or next generation either. The newly measured prompt fission neutron spectra and revisited prompt fission neutron spectra data for 235U(n,f), 239Pu(n,f) and 240Pu(n,f) reactions strongly discard the actual prompt fission neutron spectra evaluated data provided in available evaluated neutron data libraries. The reasons for that are rather diverse. The newly measured prompt fission neutron spectra are of double time of flight type. Rather wide range of the incident neutron energies, for which the outgoing prompt fission neutrons are lumped, complicates a lot the prompt fission neutron spectra measured data fits via physical modelling, especially after the onset of the (n,xnf) reactions. In most cases the measured prompt fission neutron spectra at discrete incident neutron energies up to 20 MeV, as well as those measured with double time of flight technique were considered not correlated and their consistent analyses were almost never tried upon with rare exceptions.
Comments:
22 pages, 23 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2607.24870 [pdf]
0 citations
02
[Submitted on 27 Jul 2026]
Analytic and Approximate Solutions to Color Glass Condensate in the Classical Weak-Field Limit
S. Robicheaux · R. J. Fries
We discuss two-point functions and the energy momentum tensor of the classical gluon field after the collision of sheets of color charges on the light cone in the weak-field limit. The classical fields created by such a setup is thought to approximate the behavior of the gluon matter created right after the collision of heavy nuclei at large energies. Our discussion is based on a general expression for the gluon distribution in a nucleus, which contains the McLerran-Venugopalan (MV) Model as a special case. We derive the time-dependence of the energy momentum tensor in this general scenario. We show that the large-time behavior is universal, i.e.\ independent of the specific model for the gluon distribution, e.g.\ for energy density, transverse pressure and longitudinal pressure $ϵ, P_{T} \sim 1/ τ$ and $P_{L} \sim 1/ τ^{3}$ , where $τ$ is longitudinal proper time. Subsequently, we focus on two special cases, the MV model and a proposed improved Gaussian (iG) model with improved ultraviolet (UV) and infrared (IR) behavior, the latter inspired by earlier work by Lam and Mahlon. We explicitly discuss the time dependence of the energy momentum tensor in both models. In the case of the MV-model, for infinite colliding nuclei, it is possible to give closed-formed analytic solutions for the energy momentum tensor in terms of special functions. Components of the energy momentum tensor take the form $\sim C (m τ)^{- n} H (m τ)$ , where $n$ is an integer power, $m$ is the infrared cutoff, $H$ is a linear combination of Meijer-G functions with constant asymptotic value, and $C$ is a known constant. For the iG-model, we obtain reliable series expansions for both small and large times and show that the MV-model is recovered qualitatively in the UV limit. We briefly comment on implications for the angular momentum carried by the gluon field.
Comments:
33 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2607.25137 [pdf]
0 citations
03
[Submitted on 28 Jul 2026]
Bayesian Variational Method for Precision Few-Body Calculations
Shigeyoshi Aoyama
Many variational descriptions of quantum many-body systems rest on an expansion over basis functions, and their practical limit is often set by the number of basis functions required. We propose the Bayesian variational method (BVM), in which the basis functions are selected by Bayesian optimization: a Gaussian-process surrogate model, conditioned on the candidates evaluated so far, predicts which candidates are most likely to lower the energy, and the candidate evaluations, being mutually independent, are distributed over many nodes. Two further ingredients make the method practical. An incremental diagonalization evaluates each candidate by reusing the previous diagonalization of the accepted basis instead of solving the full eigenvalue problem anew. A trimming procedure continually removes basis functions that have become nearly linearly dependent, keeping the accepted basis small while guiding it toward the optimal solution. The BVM applies broadly to energy variational problems based on basis-function expansions in quantum mechanics; here we apply it to the Gaussian expansion method (GEM), a standard approach in few-body physics. Because the GEM basis is nonorthogonal, its linear dependence is strong, so the basis reduction achieved by the BVM is large. The reduction both accelerates the computation and, more importantly, greatly reduces the memory requirement, one of the central bottlenecks of the variational method: the reference energy of the full 32,000-dimensional GEM diagonalization is reproduced to within 0.01 K with only 705 basis functions and to within 0.001 K with 2,127, corresponding to memory reductions of 99.95% and 99.56%, since the matrix storage grows as the square of the basis dimension. Within the GEM, this opens a path to the precision study of six- and seven-body systems, and beyond, that has so far been difficult to reach.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2607.25265 [pdf]
0 citations
04
[Submitted on 28 Jul 2026]
Ab initio lattice calculation of nuclear magnetic dipole moments with systematic error quantifications
Teng Wang · Serdar Elhatisari · Xu Feng · Dean Lee · Bing-Nan Lu · Yuan-Zhuo Ma
Nuclear magnetic moments are sensitive probes of nuclear structure. However, their accurate quantitative description poses significant challenges, demanding both accurate nuclear and electromagnetic interactions as well as rigorous control of algorithmic uncertainties. Here, we present the first systematic calculation of magnetic dipole moments for selected light nuclei and aluminum isotopes within nuclear lattice effective field theory (NLEFT), an \textit{ab initio} framework applicable to medium-mass and heavy nuclei. Our calculations employ a lattice next-to-next-to-next-to-leading-order (N $^{3}$ LO) chiral interaction together with electromagnetic currents consistently derived up to the two-body level. To achieve controlled predictions, we incorporate recently developed NLEFT algorithms and perform a comprehensive assessment of algorithmic uncertainties. Within the estimated uncertainties, our results are in good overall agreement with experiment and demonstrate that two-body currents are essential for reproducing the observed magnetic moments. We further benchmark our predictions against other \textit{ab initio} calculations for light nuclei ( $A \leq 12$ ). Our work establishes a solid foundation for \textit{ab initio} studies of electroweak observables using methods that scale efficiently to medium-mass and heavy nuclei while demonstrating state-of-the-art accuracy.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex)
arXiv:
2607.25464 [pdf]
1 citation
05
[Submitted on 28 Jul 2026]
Path-length dependence of parton energy loss across collision systems: a Bayesian analysis of charged-particle RAA, consistent with a universal exponent from O+O to Pb+Pb
Fouad A. Majeed · Hussein Ali Hussein Al Naffakh · Sarah M. Obaid · Muntaha Abdullah Reishaan
How parton energy loss in the quark-gluon plasma (QGP) scales with the in-medium path length $L$ encodes the mechanism: collisional ( $Δ E \propto L$ ), radiative ( $Δ E \propto L^{2}$ ), or strong-coupling ( $Δ E \propto L^{3}$ ). Exploiting the new CERN LHC light-ion data, we extract this scaling from the system size itself, jointly analysing CMS charged-particle nuclear modification factors $R_{AA}$ in four systems - O+O, Ne+Ne, Xe+Xe and Pb+Pb - spanning mass number $A = 16$ to $208$ . A Bayesian analysis with a data-driven spectral baseline and a Monte-Carlo Glauber geometry yields an effective system-size exponent $n = 1.78 \pm 0.15 (stat) \pm 0.05 (syst)$ . Nested-sampling model selection decisively favours an effective exponent near the radiative value ( $n = 2$ ) over the collisional ( $n = 1$ ) and strong-coupling ( $n = 3$ ) values, a conclusion stable across all 160 analysis variants. Because fluctuations can only lower the effective exponent below its microscopic counterpart, the measurement bounds the latter from below at fixed geometry, excluding purely collisional energy loss. The medium density and the path length are degenerate across system size, so we quote the effective exponent as our primary result. A Bayes-factor test finds no change of regime between small and large systems, consistent with a universal exponent; the same framework gives decisive evidence for non-zero energy loss in O+O alone, quantifying the onset of suppression in the smallest system. The energy-loss magnitude corresponds to $q^/ T^{3} \approx 2$ -- $5$ , consistent with the JETSCAPE determination.
Comments:
17 pages, 15 figures, 10 tables
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2607.25727 [pdf]
0 citations
06
[Submitted on 28 Jul 2026]
Nuclear matter equation of state and astrophysics
Mateus Reinke Pelicer
Neutron-star masses, radii, and inspiral tidal deformabilities now provide quantitative constraints on the cold equation of state (\eos), favoring relatively soft matter around one to two times nuclear saturation density and substantial stiffening at larger density. These bulk constraints, however, do not uniquely determine the microscopic composition of the stellar core. Hyperons, deconfined quarks, quarkyonic matter, and strong first-order phase transitions remain viable possibilities. This article summarizes the present multimessenger status and emphasizes the next challenge---a unified description of strongly interacting matter across catalyzed neutron stars, binary mergers, and heavy-ion collisions. Recent results presented at SQM2026, including new constraints on hyperon interactions and advances in multidimensional equation-of-state modeling, highlight the complementary experimental and theoretical inputs required for this program. The MUSES Calculation Engine provides modular software infrastructure for connecting these inputs to astrophysical and heavy-ion applications.
Comments:
SQM 2026 proceeding. 6 pages
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
arXiv:
2607.25854 [pdf]
0 citations
07
[Submitted on 26 Jul 2026] (cross-list from hep-ph)
Sum-Rule-Preserving Non-Factorized Transition-GPD Tomography of $N \to Δ (1232)$ Multipole Structure
R. M. Marinaro III🇺🇸
A sum-rule-preserving transition-GPD reconstruction is developed for the $N \to Δ (1232)$ electromagnetic transition. The analysis uses published CLAS $Δ (1232)$ data, including the magnetic multipole amplitude and the electric and scalar/Coulomb quadrupole ratios, together with low- $Q^{2}$ ratio-sector constraints. Magnetic, electric, and scalar/Coulomb transition amplitudes are derived and fitted with a common library of dipole, modified-dipole, $z$ -expansion, and low- $Q^{2}$ motivated candidate forms. The fitted transition form factors define the empirical momentum-transfer normalization for a family of transition GPDs constructed to preserve the measured form-factor sum rule. Factorized, correlated non-factorized, Regge-like, and double-distribution-inspired profiles are transformed into impact-parameter space to obtain transverse densities, localization radii, higher transverse-shape moments, and multipole-resolved radial kernels. The factorized baseline yields little genuine $x$ -dependent transverse localization, while the non-factorized profiles generate distinct $x$ -dependent spatial structures under the same empirical normalization. The magnetic channel provides the most stable tomography benchmark, whereas the electric and scalar/Coulomb sectors show stronger profile sensitivity. The results demonstrate that non-factorized transition-GPD tomography can extend the factorized amplitude-to-space approach while keeping the connection to measured $N \to Δ (1232)$ transition form factors.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.24864 [pdf]
0 citations
08
[Submitted on 27 Jul 2026] (cross-list from quant-ph)
Realizing Error Suppression in Partially Fault-Tolerant Quantum Simulations with IBM Quantum Computers
Henry Froland · Dorota M. Grabowska · Sebastian Grieninger · Jeremy Hartse · Anne L. Lashbrook · Zhiyao Li · Ziyuan Li · Sarah J. M. Powell · Martin J. Savage · Xiaojun Yao · Nikita A. Zemlevskiy
Quantum error-detecting codes offer a near-term path for improving the performance of quantum simulations on noisy hardware. Using IBM's superconducting quantum computer ibm_boston, we show that partially fault-tolerant encoded quantum simulations of the Ising model in 1+1D and 2+1D outperform their unencoded counterparts in estimating local observables. To represent 42 logical qubits on the heavy-hex quantum processor, 21 blocks of the [[4, 2, 2]] Iceberg code and up to 136 physical qubits are used. By pairing fault-tolerant syndrome extraction with non-fault-tolerant logical operations, this scheme preserves many of the benefits of error detection while avoiding the overhead typically required for a fully fault-tolerant logical gate set. The encoding's square logical connectivity, together with the freedom to place logical qubits within each block, enables simulations of a 2D spatial lattice with lower circuit depth than the unencoded implementation requires. We introduce Observable-Ranked Postselection, a selective-filtering technique based on syndrome correlations that recovers reliable results without the prohibitive shot loss of full syndrome postselection. Under the cumulative effect of device errors, this encoding improves local-observable accuracy over the unencoded baseline by 2-6% at intermediate times in 1+1D simulations, growing with circuit depth to over 200% in 2+1D at the latest times studied.
Comments:
42 pages, 23 figures, 11 tables, comments welcome
Subjects:
Quantum Physics (quant-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.24947 [pdf]
1 citation
09
[Submitted on 27 Jul 2026] (cross-list from hep-ph)
Beyond leading-logarithm photon production from two-loop diagrams in a hot QCD medium
Sumit🇨🇳 · Ritesh Ghosh🇹🇼 · Munshi G. Mustafa🇮🇳
We investigate high-energy photon production from a quark-gluon plasma by evaluating the imaginary part of the two-loop photon self-energies in thermal QCD. Working within the imaginary-time formalism, we derive analytical expressions for both the leading-logarithmic and the beyond-leading-logarithmic contributions to the photon production rate. The rates obtained within the thermal field theoretical framework agree with those derived from kinetic theory calculations for the relevant photon-production processes.
Comments:
41 pages, 5 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.24950 [pdf]
0 citations
10
[Submitted on 27 Jul 2026] (cross-list from hep-ph)
Few-gluon interactions and multipole radiation in high energy nuclear collisions
Thomas A. Trainor🇺🇸
Broad claims have been made over years about achievement of quark-gluon plasma (QGP) formation in high-energy heavy-ion collisions based on certain phenomena anticipated for QGP formation. More recently, similar phenomena have appeared in smaller collision systems. In response, the original narrative associated with QGP formation has been altered, with introduction of novel concepts such as ``QGP droplets'' appearing even in p-p collisions. In contrast, alternative research has revealed novel aspects of p-p and p-Pb collisions such as exclusivity for N-N interactions and consequences of time dilation for interacting partons. Collision geometry for A-B collisions has also been shifted from conventional Glauber Monte Carlo simulations (strongly biased) to inversion of ensemble-mean $p ˉ_{t}$ data. The present study demonstrates that jet production dominates all aspects of $p_{t}$ spectrum structure and minimum-bias angular correlations over the full $p_{t}$ range of accessible data. Recently, progress has been made on interpretation of azimuth quadrupole ( $v_{2}$ ) data, reexpressed in terms of total correlated-pair number as an extensive measure, leading to inference of quadrupole $m_{t}$ spectra and quadrupole amplitude variation across all A-B collision systems that show strong indication of the effects of exclusivity. The same approach applied to jet angular correlations shows similar trends. A comprehensive quantitative description of the two QCD phenomena across all collision systems has emerged. The underlying processes are few-gluon interactions producing characteristic correlation structures corresponding to color-dipole (two-gluon, dijet) and color-quadrupole (three-gluon) radiation. That description does not rely on any role for a dense medium, multiple scattering, QGP droplets or hydro theory. It applies the same rules uniformly to small and large collision systems.
Comments:
22 pages, 18 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.25017 [pdf]
0 citations
11
[Submitted on 27 Jul 2026] (cross-list from astro-ph.SR)
Localized magnetic pressure anisotropy in strange dwarfs with crystalline crusts
Mila Leite Garcia Reis · Daniela Eller Uliana · Jaziel G. Coelho · Edson Otoniel
We study equilibrium sequences of magnetized strange dwarfs composed of a self bound MIT bag strange matter core, with $B_{\rm bag}^{1/4}=145\,{\rm MeV}$, and an ordinary crystalline crust. The aim is to determine how nuclear composition changes and magnetic pressure anisotropy in the crust modify the mass radius relation. The strange core is kept isotropic, while the crust is described either by pure nuclei stopped at the first inverse beta threshold or by electron capture sequences extended to neutron drip for C, O, Ne, and Mg compositions; selected mixed crusts are also considered up to the first instability. The stellar structure is solved with the radial pressure as the integrated pressure and with the anisotropic contribution $2(P_t-P_r)/r$ restricted to the crust. This treatment is compared with ordinary white dwarf sequences and with scalar pressure branch calculations. We find that extending the crust to neutron drip produces more compact strange dwarf branches than stopping at the inverse beta threshold, because the evolved crust is softer and the core crust transition occurs at higher pressure. Magnetic anisotropy further shifts the selected branches toward smaller radii, with the effect visible across the compositions studied and clearer at fixed stellar mass. The comparison with compact objects from the Montreal White Dwarf Database is used only as an observational reference plane, but it indicates that compact white dwarf candidates are a relevant region for testing small core strange dwarf scenarios.
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
2607.25055 [pdf]
0 citations
12
[Submitted on 27 Jul 2026] (cross-list from hep-ph)
Spin resummation of heavy quarkonium photoproduction: from the gluonic gravitational form factors to the holographic pomeron
Kiminad A. Mamo🇺🇸 · Kemal Tezgin🇺🇸 · Christian Weiss🇺🇸
Exclusive heavy quarkonium photoproduction probes the proton's gluonic structure from near-threshold (fixed-spin exchanges, gravitational form factors) to high energies (reggeized dynamics). We construct a holographic QCD amplitude that resums the even spin- $j$ gluonic exchanges, with the spin-2 input fixed by lattice QCD GFFs. The new framework describes the $J / ψ$ cross section from JLab to HERA energies in a unified manner. It explains why the spin-2 exchange model for GFF extraction near threshold is not a controlled approximation and suggests how to improve it.
Comments:
18 pages including Supplemental Material, 9 figures, 1 table
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2607.25099 [pdf]
0 citations
13
[Submitted on 28 Jul 2026] (cross-list from hep-ph)
A quark-diquark model for parity doublet structure of baryons
Bikai Gao🇯🇵 · Masayasu Harada🇯🇵
The chiral invariant mass of baryons is a phenomenological input of parity doublet models, and its microscopic origin remains an open question. We propose that the chiral invariant mass and the parity doublet structure originate from the diquarks: the scalar ( $0^{+}$ ) and pseudoscalar ( $0^{-}$ ) diquarks form a parity doublet whose invariant mass is generated by gluon dynamics rather than by the quark condensate. We construct a three-flavor chiral quark--diquark model in which a quark and a diquark are bounded into a baryon through a chiral-invariant four-body interaction whose structure is reduced from one-gluon exchange. It is shown that the quark--diquark structure automatically yields the two chiral representations and the mirror assignment of the parity doublet model, and the composite baryons acquire chiral invariant masses even for massless quarks. We find that the octet baryon spectrum and the nucleon sigma terms are reproduced very well with a minimal set of parameters. Furthermore, after chiral symmetry restoration, the model predicts a distinctive inverted mass hierarchy: the nucleon remains relatively heavy, whereas the $Σ$ and $Ξ$ baryon become lighter than the nucleon. This inverse mass ordering may therefore provide a novel, experimentally testable signature towards chiral symmetry restoration.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.25178 [pdf]
0 citations
14
[Submitted on 28 Jul 2026] (cross-list from hep-ph)
Compositeness relations for near-threshold p-wave bound states
Guo-Ying Chen🇨🇳
We generalize Weinberg's compositeness relations to near-threshold p-wave bound states and derive the relations between the p-wave effective range expansion parameters, binding energy B, and the field renormalization constant Z. We also provide the corresponding Feynman rules which are appliecable regardless of whether the near-threshold state is a pure molecular state or an elementary multiquark state.
Comments:
8 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2607.25744 [pdf]
0 citations
15
[Submitted on 28 Jul 2026] (cross-list from hep-ph)
Heavy and heavy-light mesons with arbitrary spin and parity in the Covariant Spectator Theory
Alfred Stadler🇵🇹 · Elmar P. Biernat🇵🇹
This work generalizes the one-channel Covariant Spectator Theory (CST) formalism to describe quark-antiquark mesons of arbitrary spin-parity $J^{P}$ . We also improve the quark-antiquark interaction kernel by incorporating the momentum dependence of the strong coupling. Within this framework, we perform global fits to the masses of experimentally established heavy and heavy-light mesons with $J^{P} = 0^{\pm}, 1^{\pm}, 2^{\pm},$ and $3^{\pm}$ . With only eight adjustable parameters, the model yields an excellent global description of the observed quark-antiquark spectrum and predicts both unmeasured states and likely $J^{P}$ assignments for states with unconfirmed quantum numbers. In particular, our results support the identifications of the recently observed $B_{c} (1 P)^{+}$ candidates as $0^{+}$ , $1^{+}$ , and $2^{+}$ states, and the $B_{c}^{*+}$ as the lowest $1^{-}$ state in the bottom-charm sector, as well as the $D_{s 1} (2933)^{+}$ as axial-vector state in the charm-strange sector.
Comments:
27 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2607.25747 [pdf]
0 citations
16
[Submitted on 28 Jul 2026] (cross-list from hep-ph)
Form factors of the $ρ$ -meson in chiral perturbation theory
Kakha Shamanauri🇩🇪 · Jambul Gegelia🇩🇪 · Ulf-G. Meißner🇩🇪 · Akaki Rusetsky🇩🇪
We present the calculation of the electromagnetic form factors of the $ρ$ -meson at one loop in Chiral Perturbation Theory. The power-counting-violating terms in the loop diagrams are subtracted by using infrared regularization, and the Ward identities are explicitly verified at the order considered. The results are compared to the recent calculations carried out in the framework of non-relativistic effective field theory.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2607.25844 [pdf]
0 citations

Affiliations

first authorsco-authorsvia INSPIRE