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

Affiliations

first authorsco-authorsvia INSPIRE

Prompt Fission Neutron Spectra of 233U(n, F), 235U(n, F), 239Pu(n, F) and 240Pu(n,F)

Analytic and Approximate Solutions to Color Glass Condensate in the Classical Weak-Field Limit

Bayesian Variational Method for Precision Few-Body Calculations

Ab initio lattice calculation of nuclear magnetic dipole moments with systematic error quantifications

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

Nuclear matter equation of state and astrophysics

Affiliations