Nuclear Theory·nucl-th

Monday·August 10, 2026

14 papers—8 primary·6 cross-listed

09
Millisecond-Scale Neural Operator Surrogates for Double-Null Free-Boundary Grad-Shafranov Equilibria
Plamen G. Krastev
The Grad-Shafranov (GS) equation governs ideal magnetohydrodynamic equilibrium in tokamak plasmas. Free-boundary GS solvers are central to diverted-equilibrium modeling, but nonlinear Picard iteration introduces computational cost and sample-dependent latency that can become prohibitive in optimization, modeling, and control-oriented loops. Here we train a geometrically conditioned Fourier Neural Operator (FNO) to learn a constrained forward map from spatial coordinates, scalar operating parameters $(P_{axis}, I_{p}, f_{vac})$ , and prescribed X-point locations to the poloidal-flux field $ψ (R, Z)$ . The model is trained on a controlled family of constrained double-null free-boundary equilibria generated with \textsc{FreeGS} for a single fixed machine geometry and prescribed topology. The best model achieves a mean relative $L^{2}$ error of $0.05%$ , with test error following an empirical $N^{- 0.68}$ power law over $N_{train} \in {500, 1000, 2000, 5000}$ . It recovers both X-points to within $0.2$ cm and localizes the O-point to $0.03$ cm. As a physics-consistency diagnostic, the predicted fields satisfy an external finite-difference GS residual evaluation at the same level as the ground-truth fields, with mean normalized residual $2.29$ , indistinguishable from the $2.29 \pm 0.06$ \textsc{FreeGS} baseline using the same diagnostic. The trained FNO evaluates one equilibrium in $2.77$ ms on GPU and $25.6$ ms on CPU, corresponding to speedups of $\sim 640 \times$ and $\sim 69 \times$ relative to \textsc{FreeGS} as configured here, with near-deterministic latency (p95/median $= 1.01$ ). These results show that neural-operator surrogates can provide accurate, geometrically precise, millisecond-scale equilibrium evaluations for magnetic-confinement fusion workflows within a prescribed topology and machine geometry.
↳ physics.plasm-phnucl-exnucl-thphysics.comp-ph0 citations
10
Quantum Computers will constrain the Equation of State of Neutron Stars
Adrián Castaño-García · Nahia J. Dios-Bilbao · J. J. Gálvez-Viruet · Felipe J. Llanes-Estrada · Marío Logrosán-Álvarez · Nicolás M. Arenaza · María Gómez-Rocha
The Equation of State (EoS) of Nuclear Matter at high densities, and particularly that of neutron stars, resists $ab$ $initio$ Quantum Chromodynamics (QCD) computations due to the notorious sign problem of Lattice Gauge Theory at finite chemical potential. A quantum computer deploying QCD in canonical quantization should be able to make substantial progress. We set some basic goals for a future quantum computer to predict the EoS, and thus the basic static observables of the star (mass, radius and Tidal deformability, for example). We then develop the basic theory to address the canonical Hamiltonian in Weyl (time-axial) gauge expressed in normal modes, together with the squared Gauss operator $G^{2}$ necessary to execute energy minimization algorithms restricted to the physical Fock subspace. Finally, we deploy our particle-quantum register encoding of a generic field theory to demonstrate QCD at finite chemical potential for a few (three-four) particles with a modest number of momentum modes, by simulating the quantum computer on a classical cluster. This opens the possibility for effective quantum computers to constrain the microscopic physics of neutron stars simultaneously to the operation of third--generation gravitational wave detectors such as the Einstein Telescope, providing more detailed predictions than has been possible until now.
↳ hep-phnucl-thquant-ph0 citations
11
$q q ˉ$ scattering phase shift in the $π^{0}$ channel and $π^{0}$ meson spectral function under external magnetic field and finite meson momentum
Min Zhou🇨🇳 · Zhiyang Liu🇨🇳 · Yvming Tian🇨🇳 · Chonglong Xie🇨🇳 · Guoyun Shao🇨🇳 · Shijun Mao🇨🇳
$q q ˉ$ scattering phase shift in the $π^{0}$ channel $Φ_{π^{0}} (ω^{2}, k_{⊥}^{2}, k_{3}^{2})$ and $π^{0}$ meson spectral function $ρ_{π^{0}} (ω^{2}, k_{⊥}^{2}, k_{3}^{2})$ under external magnetic field $e B$ and finite meson momentum $k_{⊥}^{2}, k_{3}^{2}$ are studied in the framework of a two-flavor Nambu-Jona-Lasinio (NJL) model. The $q q ˉ$ scattering phase shift in the $π^{0}$ channel $Φ_{π^{0}}$ is closely related to $π^{0}$ spectral function $ρ_{π^{0}}$ . We consider three situations, chiral broken phase ( $T = μ = 0$ ), chiral restoration phase ( $T > T_{p c}, μ = 0$ ) and chiral restoration phase ( $T = 0, μ > μ_{p c}$ ). For $T = μ = 0$ and $T > T_{p c}, μ = 0$ cases, $π^{0}$ meson spectral function $ρ_{π^{0}}$ shows a delta peak, several Breit-Wigner peaks and several non-Breit-Wigner peaks. The delta peak indicates the bound state of $π^{0}$ meson, and the Breit-Wigner peak means the resonant state of $π^{0}$ meson. For $T = 0, μ > μ_{p c}$ case, Pauli blocking effect plays a role, which changes the inner structure of these Breit-Wigner peaks and non-Breit-Wigner peaks. Such multiple peak structure is caused by the external magnetic field. The $q q ˉ$ scattering phase shift in the $π^{0}$ channel $Φ_{π^{0}}$ shows a jump from $0$ to $π$ when $π^{0}$ meson is in bound state. When $π^{0}$ meson is in resonant state, $Φ_{π^{0}}$ has the value $π /2$ and changes continuously. In large $ω$ region, at the starting and end points of wide peaks of spectral function, $Φ_{π^{0}}$ jumps abruptly (from $π$ to finite value or from finite value to $0$ ), and such jumps are caused by the external magnetic field. Finite momentum $k_{⊥}^{2}$ or $k_{3}^{2}$ modifies the spectral function $ρ_{π^{0}}$ and scattering phase shift $Φ_{π^{0}}$ , which demonstrates the anisotropy in the system induced by external magnetic field.
↳ hep-phnucl-th0 citations
12
Chiral Doubling of Heavy-Light Hadrons and the New Beauty--Strange $B_{s 0}^{*} (5700)^{0}$ Candidate
Maciej A. Nowak🇵🇱 · Ismail Zahed🇺🇸
The recent observation by the LHCb Collaboration of a new beauty--strange meson $B_{s 0}^{*} (5700)^{0}$ ~\cite{LHCb:2026Bs0star}, under the conditional assignment $J^{P} = 0^{+}$ provides an important new test of the chiral organization of heavy-light hadrons. More than three decades ago it was proposed that the coexistence of heavy-quark spin symmetry and spontaneously broken chiral symmetry implies that every heavy-light spin multiplet should possess an opposite-parity partner separated by a nearly universal mass gap determined primarily by the dynamics of the light degrees of freedom~\cite{Nowak:1993vc,Bardeen:1993ae}. This chiral doubling scenario was later developed into a quantitative heavy-hadron effective theory and extended to the complete charm and beauty spectra. In particular, the strange beauty sector was predicted to exhibit a parity splitting closely related to that of the strange charm sector, with only small $1/ m_{Q}$ corrections. We briefly review the symmetry origin of chiral doubling, derive the universal parity splitting through the heavy-hadron chiral effective theory, and discuss the new LHCb observation in the context of the original theoretical predictions. Taken together with the established charm spectrum, if the new beauty-strange state is confirmed to have $J^{P} = 0^{+}$ , its mass is consistent with its interpretation as the chiral partner of the ground state $B_{s}^{0}$ . Finally, we stress that the above confirmation of the spin and parity imposes in the chiral doubling scenario an existence of yet unobserved, very narrow beauty-strange meson with assignment $1^{+}$ at 5747 $\pm$ 2 MeV. This work is dedicated to the memory of our friend and collaborator Mannque Rho (1936--2026).
↳ hep-phhep-exhep-thnucl-th0 citations
13
Critical dynamics of a scalar field near four spatial dimensions
Laura Batini🇨🇭 · Eduardo Grossi🇮🇹
The critical dynamics of a non-conserved order parameter is generally expected to become overdamped at long distances, even when propagating modes occur at microscopic or intermediate scales. We investigate the critical dynamics of a scalar field theory in thermal equilibrium which, in addition to local friction and noise, also contains a time-dependent second-order kinetic term. We show how to build a supersymmetric field-theory formulation. Using a two-loop expansion about four spatial dimensions, we show that the propagating and strictly overdamped limits share the same static Gaussian and Wilson-Fisher fixed points but realize distinct dynamical scaling regimes. The overdamped limit reproduces Model A. On the surface where local friction and noise vanish, the theory instead supports an interacting propagating fixed point whose dynamic exponent receives corrections at two loops. We demonstrate that coarse-graining does not generate a local dissipative operator on this surface, which therefore remains invariant under the RG flow. Local dissipation is nevertheless relevant at the propagating fixed point: an arbitrarily small equilibrium friction-noise perturbation drives the flow away from propagating scaling. Propagating critical dynamics thus defines a consistent but fine-tuned regime that is unstable to local equilibrium dissipation.
↳ hep-thcond-mat.stat-mechhep-phnucl-th0 citations
14
Oscillations of Dissipative Neutron Stars: The Impact of Hyperonic Reaction Rates
Suprovo Ghosh🇬🇧 · Alexander Haber🇬🇧 · Nils Andersson🇬🇧 · Andrew Rhys Counsell🇬🇧
Tidal excitations of stellar oscillation modes during binary neutron-star inspirals offer a powerful probe of the composition of dense matter at supranuclear densities. Chemical equilibration plays a crucial, but often neglected, role in stellar perturbation calculations. If the chemical equilibration timescale is comparable to the oscillation timescale, then viscous effects can damp the modes. If the reactions are fast, some modes can completely disappear since their restoring force vanishes. Typically, these calculations, however, assume either instantaneous chemical equilibrium or no equilibration (frozen composition). Motivated by this, we investigate the effects of finite reaction rates on the oscillation spectrum of neutron stars containing hyperonic matter. We calculate the dominant non-leptonic weak interaction rates and incorporate them into the relativistic perturbation equations through a complex, frequency-dependent dynamical sound speed. We show that finite-rate effects naturally manifest as bulk-viscous dissipation, modifying the properties of both the fundamental ( $f$ ) and gravity ( $g$ ) modes. We further examine the impact on the tidal response by matching stellar perturbations to near-zone boundary conditions, demonstrating how viscous dissipation gives rise to a tidal lag. These results provide a consistent framework connecting microscopic reaction rates and the resulting bulk viscosity to the tidal dynamics of compact binaries, and represent a step towards incorporating viscous dissipation into gravitational-wave models of binary neutron-star inspirals.
↳ gr-qcastro-ph.HEnucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Millisecond-Scale Neural Operator Surrogates for Double-Null Free-Boundary Grad-Shafranov Equilibria

Quantum Computers will constrain the Equation of State of Neutron Stars

qqˉ​ scattering phase shift in the π0 channel and π0 meson spectral function under external magnetic field and finite meson momentum

Chiral Doubling of Heavy-Light Hadrons and the New Beauty--Strange Bs0∗​(5700)0 Candidate

Critical dynamics of a scalar field near four spatial dimensions

Oscillations of Dissipative Neutron Stars: The Impact of Hyperonic Reaction Rates

Affiliations

$q q ˉ$ scattering phase shift in the $π^{0}$ channel and $π^{0}$ meson spectral function under external magnetic field and finite meson momentum

Chiral Doubling of Heavy-Light Hadrons and the New Beauty--Strange $B_{s 0}^{*} (5700)^{0}$ Candidate