Nuclear Theory·nucl-th

Thursday·February 19, 2026

11 papers—4 primary·7 cross-listed

01
Solving BDNK diffusion using physics-informed neural networks
Vicente Chomalí-Castro · Nick Clarisse · Nicki Mullins · Jorge Noronha
In this work, we reformulate the relativistic BDNK (Bemfica-Disconzi-Noronha-Kovtun) diffusion equation in flux-conservative form, and solve the resulting equations in $(1 + 1)$ D using both a second-order Kurganov-Tadmor finite volume scheme and physics-informed neural networks (PINNs). In particular, we introduce the SA-PINN-ACTO framework, which combines the self-adaptive PINN technique with an exact enforcement of initial and periodic boundary conditions through an algebraic transform of the network's raw output, allowing the network to focus solely on minimizing the PDE residual. We test both approaches on smooth and discontinuous initial data, for both trivial and dynamically evolving velocity and temperature BDNK backgrounds, and for two characteristic speeds. The SA-PINN-ACTO method matches the converged Kurganov-Tadmor solutions for smooth profiles, while for discontinuous profiles the errors increase, reflecting an expected limitation of PINNs near sharp gradients.
nucl-thastro-ph.HEgr-qc1 citation
02
Rapidity dependence of mean transverse momentum fluctuation and decorrelation in baryon-dense medium
Tribhuban Parida🇵🇱
I study the event-by-event fluctuation and rapidity decorrelation of the mean transverse momentum $\spt$ , which has recently been proposed as a sensitive probe of the equation of state at finite baryon density. The investigation reveals that, in a baryon-rich medium, the event-by-event fluctuation of the mean transverse momentum is driven by the combined effects of energy-density and net-baryon-density fluctuations. Consequently, the rapidity dependence of this observable provides a promising handle to probe the three-dimensional structure of both energy and baryon density profiles. Previous studies have shown that $\spt$ decorrelation along rapidity is largely insensitive to shear and bulk viscosity; however, its dependence on baryon diffusion, another key transport coefficient in baryonic matter, has not been explored. I find that baryon diffusion has a negligible impact, establishing this observable as a robust probe of the equation of state. Furthermore, I present predictions for identified hadrons and observe a pronounced splitting in the rapidity decorrelation of mean transverse momentum between protons and antiprotons, indicating different transverse flow dynamics for baryons and antibaryons.
nucl-thhep-phnucl-exPRC(2026)·1 citation
03
The Crusts of Neutron Stars Revisited: Approximations within a Polytropic Equation of State Approach
F. Köpp · J. E. Horvath · C. A. Z. Vasconcellos
In this work, we revisit several thin-crust approximations presented in the literature and compare them with the exact solutions of the Tolman--Oppenheimer--Volkoff (TOV) equations. In addition, we employ three different equations of state (EoSs), including one with a pasta phase, each based on a distinct theoretical framework: the variational method, relativistic Brueckner--Hartree--Fock theory, and relativistic mean-field theory. We emphasize that these approximations require only the TOV solutions for the core and the EoS properties at the core--crust interface; in our approach, only the energy density is needed. Finally, the relativistic approximation, as well as the Newtonian approximation with corrections, shows good agreement with the exact solutions. This indicates that a simple treatment of the crust is sufficient for structural purposes, independently of the uncertainties in the sub-nuclear equation of state, which are not very large. The unified EoS SINPA (relativistic mean-field theory), including the pasta phase, was used to study the thin-crust approximation, while degeneracy in the $M$ -- $R$ relation is demonstrated through: (i) anisotropic pressure in the modified TOV equations, (ii) the $f (R, L_{m}, T)$ gravity model, and (iii) dark matter admixture. As demonstrated, modifications to the description of gravitation introduce degeneracies in the mass--radius relation that are challenging to disentangle or quantify precisely.
nucl-thEPJC(2026)·1 citation
04
Comparison of Pauli projection and supersymetric transformation methods for three-body nuclear structure and reactions
A. Deltuva
Three-body Faddeev-type equations for bound, resonant, and scattering states in the systems with a nuclear core and two nucleons are solved using the momentum-space framework. Two approaches for eliminating the Pauli-forbidden deeply-bound states are compared: projecting out those states by a nonlocal term in the potential, and by using a supersymmetric transformation of the potential. While the former method is preferred by the experimental data for the deuteron- $^{4}$ {He} scattering, the results for bound and resonant states do not indicate a clear superiority of a single method. Instead, systematic differences between them are found.
nucl-thnucl-exPRC(2026)·0 citations
05
The role of \nu_{\tau} ultrahigh energy astrophysics in Km^3 detectors
D.Fargion (Physics Dept. Rome University 1, INFN Rome, Italy; Faculty of Electrical Engineering Technion-Israel Institute of Technology, Haifa, Israel)🇮🇹
We show that the expected $ν_{τ}$ signals, by their secondary tau tracks, in Km^3 detectors at highest cosmic ray energy window $1.7 \cdot 1 0^{21} e V > E_{τ} > 1.6 x 1 0^{17} e V$ , must overcome the corresponding $ν_{μ}$ (or muonic) ones. Indeed, the Lorentz-boosted tau range length grows (linearly) above muon range, for $E_{τ} \RAISE 1.6 x 1 0^{8} G e V$ and reaches its maxima extension, $R_{τ_{m a x}} ≃ 191 k m$ , at energy $E_{τ} ≃ 3.8 x 1 0^{9} G e V$ . At this peak the tau range is nearly 20 times the corresponding muon range (at the same energy) implying a similar ratio in $ν_{τ}$ over $ν_{μ}$ detectability. This dominance, however may lead (at present most abundant $ν_{τ}$ model fluxes) to just a rare spectacular event a year (if flavor mixing occurs). Lower energetic $τ$ and $ν_{τ}$ signals $(ν ˉ_{e} e \to ν ˉ_{τ} τ, ν_{τ} N \to ...)$ at energy range ( $1 0^{5} \div 1 0^{7} G e V$ ) may be more easily observed in km^3 detectors at a rate of a few $(ν ˉ_{e} e \to ν ˉ_{τ} τ)$ to tens event $(ν_{τ} N \to τ +$ anything) a year.
↳ astro-phastro-ph.HEhep-phnucl-ex+162 citations
06
A compendium of cold-nuclear matter baseline predictions in light-ion collisions
Florian Jonas🇨🇭 · Constantin Loizides🇺🇸 · Aleksas Mazeliauskas🇩🇪 · Petja Paakkinen🇨🇭 · Nicolas Strangmann🇩🇪
The recent light-ion collision programme at RHIC and the LHC provides a unique opportunity to investigate the onset of quark-gluon plasma formation and parton energy loss in small systems. A quantitative interpretation of emerging jet quenching measurements requires precise control over cold nuclear matter (CNM) effects, which modify hard-process cross sections independently of any hot-medium dynamics. In this work, we present a comprehensive set of perturbative QCD baseline calculations for nuclear modification factors ( $R_{AA}$ ) in proton-oxygen (pO), oxygen-oxygen (OO) and neon-neon (NeNe) collisions at LHC energies. The study includes charged hadron, neutral pion, prompt photon, and electroweak-boson production computed at next-to-leading order using a broad set of recent nuclear parton distribution functions (nPDFs). We demonstrate that CNM effects alone can induce sizeable suppressions in light-ion systems, with large associated nPDF uncertainties that currently limit the quantitative extraction of parton energy loss. To address this limitation, we explore a range of multi-cross-section ratios in which CNM effects and their uncertainties largely cancel. In particular, ratios of neutral pion $R_{O O}$ to prompt photon $R_{O O}$ or charged hadron $R_{O O}$ to $R_{pO}^{2}$ provide theoretically robust observables with substantially reduced nPDF uncertainties, thereby enhancing sensitivity to possible energy-loss signatures.
↳ hep-phnucl-exnucl-thEPJC(2026)·8 citations
07
Tensor Polarizability of the Nucleus and Angular Mixing in Muonic Deuterium
G. S. Adkins🇺🇸 · U. D. Jentschura🇺🇸
We investigate the effects of the tensor polarizability of a nucleus on the bound-state energy levels, and obtain a general formula for the contribution of the tensor polarizability to the energy levels in two-body bound systems. In particular, it is demonstrated that the tensor polarizability leads to mixing between states with different orbital angular momenta. The effect of tensor polarizability is evaluated for the hyperfine-structure components of P states and for the mixing of S and D states in muonic deuterium.
↳ physics.atom-phhep-phnucl-thPRA(2026)·0 citations
08
Electromagnetic Production of Kaons on the Nucleon
Terry Mart🇮🇩 · Jovan Alfian Djaja🇮🇩 · Daniel S. Carman🇺🇸
Studies of the electromagnetic production of strange quarks began in the 1950s as something of a curiosity that puzzled experimentalists and theorists alike. As the datasets increased, concomitant advances in theoretical models were realized. A paradigm shift occurred in the 1990s with the development of second-generation facilities at ELSA, MAMI, SPring-8, and JLab, which brought nuclear physics experiments forward by orders of magnitude in counting statistics compared to the first-generation efforts. This was an utter boon to strangeness physics investigations, and to date, more than 50 dedicated experiments in kaon photo- and electroproduction have been completed at facilities around the world, leading to a host of experimental observables that have enabled significant advances in the exploration of strongly interacting systems that decay via $s s ˉ$ quark pair creation. This review was designed to provide the first-ever in-depth overview of both the experimental and theoretical progress in the field of the electromagnetic production of strangeness. This work looks back over 70 years of past developments, discusses ongoing work and near-term plans, and details future possibilities being considered for third-generation facilities. Throughout this work, the primary impacts of these explorations are highlighted, along with connections to a wide range of related phenomenological applications. An important goal of this review is to provide a complete, self-contained guide into this field prepared at a level that is relevant for both new and seasoned scientists, whether experimentalists, phenomenologists, or theorists, to better understand what has been accomplished by so many dedicated folks-each building on what has come before-and to appreciate the exciting future potential for continued studies in this area. A more complete abstract is provided in the paper.
↳ hep-phhep-exnucl-exnucl-thPPNP(2026)·2 citations
09
Momentum Broadening in the Opacity Expansion: All-Path-Length Corrections and Improved Regge Kinematics
Dario van den Berg🇿🇦 · Isobel Kolbé🇿🇦
We present a detailed study of momentum broadening and the jet transport coefficient $q^$ for high-energy partons traversing the Quark-Gluon Plasma (QGP), extending the Gyulassy-Levai-Vitev (GLV) formalism to include both all-path-length (APL) and sub-Regge kinematical corrections. Traditional GLV calculations rely on the large separation distance and large formation time approximations, which are valid for large systems but whose applicability to small systems, such as $pp$ and $p / d$ A collisions, may fail. We derive analytic expressions for the momentum broadening distributions and $q^$ to first order in the opacity expansion, and perform a detailed numerical investigation to quantify their impact. The APL correction suppresses momentum broadening at low $p_{⊥}$ , with a correction scaling as $\propto 1/ (L p_{⊥})$ that dominates for small systems, while converging to the standard GLV result at large $L$ . The sub-Regge kinematical correction enhances momentum broadening at high $p_{⊥}$ , becoming significant when the transverse momentum transfer approaches the magnitude of the parton's large light-cone momentum component, and vanishing in the Regge limit where this ratio is small. When both corrections are combined, the sub-Regge kinematical correction partially mitigates the suppression induced by the APL term; in the case of $q^$ , this mitigation is essentially complete, with $q^_{(APL + SUB)}$ found to coincide closely with the standard GLV result. These findings demonstrate that sub-Regge kinematical corrections can resolve the long-standing problem of large negative energy-loss contributions at high energies identified in earlier studies.
↳ hep-phnucl-th1 citation
10
Isospin dependence of nuclear EMC effect from global QCD analysis
C. Cocuzza🇺🇸 · T. J. Hague🇺🇸 · W. Melnitchouk🇺🇸 · N. Sato🇺🇸 · A.W. Thomas🇦🇺
We perform a new global QCD analysis of unpolarized parton distribution functions (PDFs) in the nucleon from proton, deuteron and $A = 3$ data, including recent measurements of $^{3}$ He/ $D$ and $^{3}$ H/ $D$ cross section ratios from the MARATHON experiment at Jefferson Lab. Simultaneously inferring the PDFs and nucleon off-shell corrections allows both to be determined consistently, without theoretical assumptions about the isospin dependence of nuclear effects. The analysis provides strong evidence for the need of nucleon off-shell corrections to describe the $A = 3$ data, with large isoscalar and a suggestion of nonzero isovector contributions in $A \leq 3$ nuclei. We find that the extracted EMC ratios of nuclear to nucleon structure functions for $A = 2$ and 3 differ from those naively extrapolated from heavy nuclei down to low $A$ .
↳ hep-phhep-exnucl-th5 citations
11
The spatial Wilson loops, string breaking, and AdS/QCD
Oleg Andreev🇩🇪
We consider the phenomenon of string breaking in the context of the spatial Wilson loops using the gauge/string duality. In particular, we discuss the impact of light flavors on the pseudopotential. We also introduce the notion of the spatial string breaking distance and estimate it for $S U (3)$ gauge theory in the temperature range $0 - 3 T_{c}$ .
↳ hep-phhep-lathep-thnucl-thPLB(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE