Nuclear Theory·nucl-th

Tue·Sep 29, 2026Tuesday·September 29, 2026

15 papers—9 primary·6 cross-listed

01
Global equilibrium at order $O (ℏ^{2})$ : pseudo-gauge ambiguity, Maxwell relations, and thermodynamic consistency
Asaad Daher · David Wagner · Masoud Shokri · Dirk H. Rischke
We study massive spin- $1/2$ Boltzmann particles in global thermodynamic equilibrium with rotation and acceleration, consistently including quantum corrections up to order $O (ℏ^{2})$ . For such a system, the fluid velocity becomes an independent thermodynamic variable and fundamental thermodynamic relations have to be extended. Employing the Wigner-function formalism, we show that the standard mass-shell condition $k^{2} = m^{2}$ is modified at order $O (ℏ^{2})$ by contributions quadratic in the thermal vorticity. Incorporating this modified mass-shell constraint, we derive the (net) particle-number current, energy-momentum tensor, spin-current tensor, and associated thermodynamic quantities in the kinetic, canonical, and de Groot--van Leeuwen--van Weert (GLW) pseudo-gauges. We explicitly demonstrate that, while global quantities, like the total particle number or total energy, are independent of the choice of pseudo-gauge, local quantities, like the particle-number density or the energy density, are pseudo-gauge dependent. We then examine the thermodynamic relations in each pseudo-gauge and demonstrate that thermodynamic consistency requires that the thermodynamic Maxwell relations are satisfied. We find that these relations hold in the kinetic-theory pseudo-gauge, whereas they are in general violated in the canonical and GLW pseudo-gauges. These findings suggest a preference for using the kinetic-theory pseudo-gauge in applications such as spin hydrodynamics.
nucl-thhep-phhep-th
02
Structure and decay of $^{21}$ B resonances
R. Alvarez-Rodriguez · E. Garrido
The structure of the neutron-rich nucleus $^{21}$ B is investigated within a three-body model consisting of a $^{19}$ B core and two neutrons. The three-body wave functions are computed using the hyperspherical adiabatic expansion method combined with the complex-scaling technique. Four potential parametrizations compatible with the available experimental information on $^{20}$ B are considered. The calculations predict a low-lying $\frac{3}{2}^{-}$ state below the experimentally observed resonance at 2.47~MeV. An analysis of the dependence on the three-body interaction shows that this state cannot be shifted to the experimental resonance energy; instead, it remains either bound or becomes a near-threshold resonance with a rapidly increasing width. These results indicate that the observed resonance is more naturally interpreted as the second $\frac{3}{2}^{-}$ state, whereas a lower-lying $\frac{3}{2}^{-}$ state, dominated by an $s_{1/2}$ configuration, has so far eluded experimental observation. Momentum correlations are obtained for the experimentally observed resonance. In addition, the existence of other resonances is investigated.
nucl-th
03
$β$ Recoil spectroscopy as a Beyond Standard Model laboratory
Leendert Hayen
We consider the nuclear recoil spectrum following allowed $β$ decay as a laboratory for Beyond Standard Model searches, and perform an exhaustive treatment of the Standard Model prediction. We consider final state interactions, nuclear structure corrections, kinematic corrections and radiative corrections, derive new results and show that the nuclear recoil spectrum is theoretically exceptionally clean. We construct a clean statistical framework and analyze the Fisher information for extracting exotic current constraints and testing Cabibbo-Kobayashi-Maskawa top-row unitarity, and consider a number of sterile neutrino scenarios. In addition, we find that for select isotopes separate measurement of the $β$ -asymmetry and recoil spectrum can achieve an increase in the statistical power of up to a factor 40.
nucl-thhep-phnucl-ex
04
Nuclear scattering phase shifts with factorized geometric-time RODEO on a quantum processor
Myeong-Hwan Mun · Jubin Park · Myung-Ki Cheoun · Eunja Ha
We reconstruct elastic $s$ -wave neutron-proton ( $n p$ ) phase shifts from trapped spectra measured on IBM Aachen using a compressed RODEO circuit. For a schematic square-well interaction represented by classically constructed four-dimensional effective Hamiltonians, four positive-energy levels at five trap strengths supply twenty inputs to classical modified effective range expansion (MERE) extrapolation to free space. The six-cycle factorized geometric-time RODEO implementation (FG-R6) combines ancilla reuse, exact query-phase separation, post-compilation binding, and six numerically optimized geometric evolution times. Numerical cycle-count tests support this choice within the adopted local spectral tolerances. At the same three-qubit width and equal shot budgets, FG-R6 reduces median compiled depth and two-qubit-gate count by 33.1% and 37.2% relative to ten-cycle dynamic direct RODEO (direct R10), increases the median fitted amplitude, and lowers median finite-shot energy uncertainty from 0.610 to 0.534 keV. For this dataset's primary fit on the 0.1-30.0 MeV grid, the maximum central phase-shift deviation from exact-energy MERE decreases from $0.84 2^{\circ}$ to $0.16 3^{\circ}$ , despite a larger root-mean-square (RMS) trapped-energy deviation. The full-grid gain arises mainly in the low-energy extrapolation region; direct R10 has slightly smaller residuals relative to the same reference on the 10.0-30.0 MeV common energy-interpolation subset. The FG-R6 central curve differs from the analytical square-well solution by at most $0.15 6^{\circ}$ . Fit-form sensitivity remains appreciable and is assessed separately from finite-shot uncertainty. This reduced-space benchmark connects RODEO circuit compression to nuclear continuum observables and shows why circuit performance must be assessed through the scattering reconstruction and its energy range, not spectral RMS errors alone.
nucl-thquant-ph
05
Medium effects on neutron star modified and direct Urca cooling rates
B. X. Zhou · Jin-Biao Wei · Z. H. Li · G. F. Burgio · H.-J. Schulze
We study the effects of in-medium modification of the elementary cooling processes on observable properties of isolated neutron stars. We then deduce the neutron star mass distributions compatible with the cooling analysis and compare with current theoretical models. We conclude that current cooling data require fast direct Urca (DU) cooling, moderated by proton superfluidity, to be active in most neutron stars, and that the DU onset threshold must lie below canonical masses. In that case medium modifications of modified Urca (MU) rates are practically insignificant, but the $nn$ Bremsstrahlung rate plays a dominant role.
nucl-thastro-ph.HE
06
Strongly interacting fermions under imaginary rotation
Tudor Pătuleanu · Victor E. Ambrus
In the present study, we investigate the phase diagram of strongly-interacting fermions under imaginary rotation. We employ the linear sigma model coupled to quarks in the mean field approximation. The fermion expectation values are computed in the local density approximation (LDA), using the well-known expressions derived using cylindrical modes for states under rigid rotation, at finite temperature $T$ and chemical potential $μ$ . We study the impact of the fractalization of thermodynamics on the phase diagram in the far-field limit (far from the rotation axis). We also reveal non-trivial features such as a complete inhibition of the chiral symmetry restoration on the rotation axis above a critical imaginary angular velocity. We demonstrate explicitly how the transition line interpolates between its shape on the rotation axis and in the far-field limit by studying the chiral phase transition at finite distances from the rotation axis. We also address the moment of inertia of the system and discuss differences and similarities to lattice studies of QCD matter under imaginary rotation.
nucl-thhep-phhep-th
07
Modelling fission with microscopic input: excitation-energy-dependent fission paths for neutron-induced reactions
Adrián Sánchez-Fernández · Wouter Ryssens · Stéphane Goriely
To calculate transmission coefficients, current Hauser-Feshbach reaction codes assume a one-dimensional fission path that is both independent of excitation energy and universal across different fission channels. In contrast, microscopic fission studies typically explore multiple collective variables. Predicting observable fission quantities such as cross sections based on microscopic input thus requires a way to reduce the dimensionality of the latter. For spontaneous fission, the least action path (LAP) -- which minimizes the semiclassical action and maximizes the transmission coefficient -- is the solution. We demonstrate that the LAP does not generalize to other fission modes such as neutron-induced or $β$ -delayed fission: at finite excitation energy, the LAP generally does not maximize the transmission. A microscopic PES can have multiple coexisting stationary-action paths. We show that these (i) can switch their action ordering as a function of excitation energy and (ii) yield different neutron-induced fission cross sections predictions, yet match known spontaneous fission lifetimes equally well. For the BSkG3 Skyrme-type energy density functional model, the transition from the axially symmetric LAP at zero excitation energy to a path exploiting the triaxial degree of freedom occurs at an excitation energy that is smaller than the neutron separation energy for essentially all actinides and the majority of unknown exotic nuclei.
nucl-th
08
ShARK: A Stochastic Transport Framework for the Relativistic Relaxation Time Approximation Boltzmann Equation
Tiago Nunes da Silva · Jadna L. Barauna · Giorgio Torrieri
We show that the Anderson-Witting relaxation-time approximation (relativistic Bhatnagar-Gross-Krook (BGK) equation) emerges as the $N \to \infty$ limit of a stochastic $N$ -body particle gas, in which collisions perform a full microcanonical momentum redraw that enforces local energy-momentum conservation at every event. Using the RAMBO algorithm to sample the Lorentz-invariant phase space, we derive the finite- $N$ single-particle momentum spectrum and show that it converges to the Jüttner-Boltzmann equilibrium distribution as the local particle number grows. We couple this relaxation kernel to an advection-relaxation splitting scheme to construct ShARK (Stochastic Advection Relaxation Kinetics), a 3D Monte Carlo relativistic solver for the relaxation time approximation Boltzmann equation. The framework is conceptually related to lattice Boltzmann methods, but formulated in continuous momentum space to avoid the accuracy loss caused by finite-order momentum discretizations far from local equilibrium. We validate the numerical results against analytical solutions for two highly symmetric conformal expansions, the Bjorken and Gubser flows. The framework provides a first-principles route to far-from-equilibrium relativistic transport, with applications ranging from heavy-ion collisions to expanding astrophysical plasmas.
nucl-thhep-ph
09
Relaxation-Time Boltzmann Solutions Without Truncations
Tiago Nunes da Silva · Jadna L. Barauna · Giorgio Torrieri
The relaxation-time Boltzmann equation governs relativistic matter far from equilibrium, but existing approaches rely on finite-order truncations that break down in this regime. We introduce ShARK (Stochastic Advection Relaxation Kinetics), the first fully 3D Monte Carlo kinetic framework to capture exact, far-from-equilibrium ultrarelativistic dynamics for arbitrary initial conditions while directly enforcing target transport coefficients, converging to the exact Anderson-Witting solution. Validated against the Bjorken and Gubser flows, the framework reproduces the exact kinetic result where truncated methods fail.
nucl-thhep-ph
10
Scattering amplitudes from quantum hardware a la RESOs
Raul A Briceno · Ivan M Burbano · Anthony N Ciavarella · Ermal Rrapaj · Thomas R Richardson · Andre Walker-Loud
We report the first quantum-hardware implementation of Real-time Estimators for Scattering Observables (RESOs). The physical model is a one-dimensional lattice theory of non-relativistic spin-1/2 fermions with a single contact interaction. The lattice sizes studied are up to $N_{x} = 54$ lattice sites and up to $20$ time steps. Spacetime correlation functions were computed on IBM's quantum computers, using $109$ qubits with $10, 806$ CZ gates applied, reaching a two-qubit gate depth of $246$ . We demonstrate how to study bound states and extract scattering amplitudes from these correlation functions.
↳ quant-phhep-latnucl-th
11
Dissecting the moat regime at low energies II: Correlations
Fabian Rennecke · Shi Yin
We study the effects of the moat regime on meson and quark correlation functions and the quark-antiquark potential in low-energy QCD, building on the two-flavor quark meson model in a random-phase approximation. We investigate the relation between the moat regime and Friedel oscillations in the quark-antiquark potential at large density and zero temperature. As it turns out, oscillations from the moat regime are a distinct phenomenon, arising from poles on unphysical Riemann sheets in this region. Furthermore, we find that in addition to pions and the sigma meson, also other mesons, including vector mesons and the eta, are sensitive to the moat regime. This leads in particular to an enhancement of the meson spectral function in the spacelike region. The quarks, on the other hand, appear to be essentially insensitive. This can have far-reaching consequences for the phase diagram, as for example the chiral phase boundary, including the location of the critical endpoint, can be affected in the moat regime even in absence of inhomogeneous instabilities.
↳ hep-phhep-thnucl-th
12
Landscape of pentaquark bound states with neural-network Variational Monte Carlo
Jing-Zhe Song · Wei-Lin Wu · Shi-Lin Zhu
We present a systematic study of the ground states of pentaquark systems using the neural network variational Monte Carlo method within the constituent quark potential model. We investigate all manifestly exotic pentaquark systems with negative parity, which cannot mix with the conventional baryons through the creation and annihilation of light or strange quark pair. We exhaust 387 color, spin, and isospin configurations and identify 21 pentaquark bound state candidates with binding energies ranging from $2$ to $15$ MeV. A striking observation is that all of the bound states are shallowly bound molecular states, and a deeply bound pentaquark state does not exist. The $QQq q Q ˉ$ , $ss q q Q ˉ$ , $Q s q q Q ˉ$ and $Qq q q Q ˉ$ bound states are composed of a heavy vector meson and a baryon, while the $QQq q s ˉ$ and $Qq q q s ˉ$ bound states are composed of a $K$ meson and a heavy baryon. As a cross-validation, the ground-state energies of the unbound systems converge to the baryon--meson thresholds from above, which are consistent with the S-wave scattering states and provide a reliable baseline for the bound-state criterion. Especially, we reproduce the lowest scattering states $η_{c} N$ and $η_{c} Λ$ in the $q q q c c ˉ$ and $q q sc c ˉ$ channels respectively, where the hidden-charm pentaquark resonances were observed experimentally. We also find that all fully heavy pentaquark states are unbound. Our results provide valuable guidance for future pentaquark searches at LHCb, Belle II, and other experiments.
↳ hep-phhep-exhep-latnucl-th
13
Quantum tomography at the Electron-Ion Collider
Michael Fucilla · Yuxun Guo · Yoshitaka Hatta
We initiate the study of quantum state tomography---the experimental reconstruction of the complete spin density matrix---of massless and massive quark-antiquark pairs produced at the future Electron-Ion Collider (EIC). We show that all components of the spin density matrix can be accessed through azimuthal angular correlations between hadron and dihadron pairs generated by the Collins and dihadron fragmentation functions. This enables the experimental investigation of a variety of quantum information properties at the EIC, such as entanglement and Bell-nonlocality. We predict that the recently discovered maximal entanglement in the heavy-quark sector is signaled by a strong modification of the usual Collins angular dependence $cos (ϕ + ϕ^{'})$
↳ hep-phhep-exnucl-th
14
$K ˉ^{0} d$ Bound State and Correlation Function
M. Bayar · P. Encarnación · A. Feijoo · E. Oset
We study the $K ˉ^{0} d$ system using a new formulation of the fixed-center approximation that preserves elastic unitarity. The resulting scattering amplitude predicts a bound state below threshold, which can be interpreted as a $Λ (1380) N$ configuration complementary to the $K^{-} pp$ state associated with the higher $Λ (1405)$ pole. The interaction is attractive, with scattering parameters of the same order as recent $K^{-} d$ determinations. We further calculate the $K ˉ^{0} d$ correlation function, which exhibits a characteristic structure associated with the bound state and provides a Coulomb-free observable that can be tested in future ALICE measurements. Results obtained with two different $K ˉ N$ models are very similar, indicating the robustness of the predictions against the choice of the underlying interaction.
↳ hep-phnucl-th
15
Stress in static force fields and the sign of the D-term
Adam Freese
The sign of the D-term is negative for a variety of hadrons, including the proton and pion. Speculation that this is the result of a mechanical stability condition has persisted despite counterexamples, including the positive D-term of the hydrogen atom. In this work, I explore how the sign of the D-term is influenced by the stress carried by static abelian force fields, finding the contributions from spin-even fields to be negative and the contributions from spin-odd fields (such as the electromagnetic field) to be positive. These contributions correlate with the signs of the D-terms of the fields' respective quanta. Since fields with different spin can produce identical potentials---thus resulting in equally-stable composite systems with identical wave functions---the sign of the D-term has nothing to do with stability. Since hadrons are bound by spin-one gluons, their negative D-terms appear atypical and require explanation. I briefly speculate on how color flux confinement could produce a negative hadronic D-term.
↳ hep-phnucl-th