Nuclear Theory·nucl-th

Tuesday·April 21, 2026

12 papers—4 primary·8 cross-listed

05
[Submitted on 17 Apr 2026] (cross-list from hep-ph)
Four-fermion operators, $Z$ -boson exchange, and $τ$ lepton dipole moments
Joël Gogniat🇨🇭 · Martin Hoferichter🇨🇭 · Gabriele Levati🇨🇭
Asymmetry measurements in $e^{+} e^{-} \to τ^{+} τ^{-}$ constitute a promising avenue to obtain competitive constraints on the $τ$ dipole moments, the anomalous magnetic moment $a_{τ}$ and the electric dipole moment $d_{τ}$ , especially, once a polarized electron beam becomes available, as possible at a future polarization upgrade of the SuperKEKB collider. While the main challenges concern the measurement of these asymmetries and the calculation of radiative corrections at the relevant level of precision, at subleading orders also electroweak effects and the potential impact of four-fermion operators parameterizing other beyond-the-Standard-Model scenarios besides those described by dipole operators need to be taken into consideration. Here, we show that $Z$ -boson contributions arise at the level of $≃ 3 \times 1 0^{- 6}$ , while we estimate the largest possible effect from four-fermion operators as $≃ 1 0^{- 5} C v^{2} / Λ^{2}$ . In addition, we observe that four-fermion-operator insertions at the loop level can probe Wilson coefficients that are otherwise not constrained directly, and that the imaginary part generated by insertions of the dipole operator at loop level opens another potential avenue towards a determination of $a_{τ}$ without the need for a polarized electron beam. Despite the inherent loop suppression, a measurement of the required normal asymmetry $A_{N}^{\pm}$ with a precision of $≲ 1 0^{- 5}$ would allow one to probe the Schwinger term, which could define an intermediate goal to be realized in the current setting at Belle II.
Comments:
9 pages, 2 figures; journal version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2604.16598 [pdf]
PLB(2026)·5 citations
06
[Submitted on 17 Apr 2026] (cross-list from astro-ph.CO)
A data-driven prediction for the primordial deuterium abundance
Timothy Launders · Cara Giovanetti · Hongwan Liu
We predict the primordial deuterium abundance using a novel, fully data-driven approach, where we use Gaussian process regression to fit experimental nuclear reaction data for $d$ ,( $d$ , $n$ ) $^{3}$ He, $d$ ,( $d$ , $p$ ) $t$ , and $d$ ( $p$ , $γ$ ) $^{3}$ He, three reactions to which the primordial deuterium abundance is most sensitive. Using the Planck determination of the baryon density, we predict $1 0^{5} \times D/H = 2.442 \pm 0.040$ in standard Big Bang Nucleosynthesis, $1.70 σ$ below the Cooke et al. measurement. Our result is consistent with predictions relying on first principles calculations of the deuterium burning cross sections. With the inferred baryon density from a combined fit to Planck, ACT DR6, and SPT-3G D1, this discrepancy worsens to $1.98 σ$ . We validate our approach and confirm that Gaussian processes make unbiased D/H predictions with appropriately-sized uncertainties. We repeat our validation tests for low-degree polynomial fits, a technique used in previous analyses, and find that they systematically over-predict D/H. Our results highlight the need for improved measurements of the $d$ ,( $d$ , $n$ ) $^{3}$ He and $d$ ,( $d$ , $p$ ) $t$ S-factors at energies between 0.1 and 0.6 MeV.
Comments:
(7 pages, 4 figures in main body; 14 pages, 9 figures Supplemental)
Subjects:
Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2604.16600 [pdf]
8 citations
07
[Submitted on 19 Apr 2026] (cross-list from hep-ph)
Boost-invariant perfect Fermi-Dirac spin hydrodynamics
Zbigniew Drogosz🇵🇱 · Natalia Łygan🇵🇱
We analyze the effect of using the Fermi-Dirac statistics, rather than its Boltzmann approximation, in numerical simulations of perfect spin hydrodynamics of particles with spin 1/2. The system considered is boost invariant, transversely homogeneous, with corrections to the baryon current and the energy-momentum tensor that are second order in the spin polarization tensor $ω$ , and the spin tensor considered is first order in $ω$ . The study shows the feasibility of this approach, as the special functions defined by integrals that appear in the coefficients in the Fermi-Dirac case can be conveniently parametrized. For sets of initial conditions used in previous works, the differences in parameter evolution between the two underlying particle statistics are about one order of magnitude smaller than corrections coming from spin feedback. We also discuss when and why the numerical solutions of the equations of perfect spin hydrodynamics break down for very large values of spin polarization in one of the geometric configurations considered.
Comments:
24 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2604.17392 [pdf]
Acta Phys.Polon.B(2026)·1 citation
08
[Submitted on 19 Apr 2026] (cross-list from hep-th)
A Note on Coadjoint Orbits for Multifermion Systems
V.P. Nair🇺🇸
The coadjoint orbit action for a multifermion system, as an exact description of its dynamics, is considered. A parametrization of the variables involved is given which facilitates the approximation of this by another coadjoint orbit action suitable for expansions around the Fermi surface, recovering various actions which have been used in previous literature. The presentation of this in terms of functions on phase space with star-products as well as further truncations are briefly considered.
Comments:
18 pages
Subjects:
High Energy Physics — Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th)
arXiv:
2604.17491 [pdf]
0 citations
09
[Submitted on 20 Apr 2026] (cross-list from hep-ph)
Polarization, Maximal Concurrence, and Pure States in High-Energy Collisions
Yu-Xuan Liu🇨🇳 · Wei Qi🇺🇸 · Luo-Ting He🇨🇳 · Bo-Wen Xiao🇨🇳
We establish a quantitative relation between local spin polarization and quantum entanglement in two-qubit systems by mathematically proving a closed-form upper bound on the concurrence at fixed local polarization magnitudes. The bound shows how the maximal concurrence is jointly constrained by the two local polarizations. We further demonstrate that this bound is saturated by pure states in certain cases with identical polarizations. As a concrete physical application, we consider the parity-violating process $e^{+} e^{-} \to Z^{0} \to q q ˉ$ , which generates final-state spin polarization. We show that the maximal concurrence is attained in specific kinematic regions and is significantly reduced relative to the unpolarized case. These results establish a general, process-independent framework connecting local polarization, maximal entanglement, and pure states.
Comments:
20 pages, 3 figures; V3: Detailed proof and minor updates are provided
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
2604.17756 [pdf]
8 citations
10
[Submitted on 20 Apr 2026] (cross-list from hep-ph)
Compositeness of near-threshold eigenstates with Coulomb plus short-range interactions
Tomona Kinugawa · Tetsuo Hyodo
We investigate the internal structure of near-threshold $s$ -wave eigenstates in a two-body system with Coulomb plus short-range interactions. Using a nonrelativistic effective field theory, we derive the expression for the compositeness in terms of the energy derivative of the self-energy, which is applicable to the present system with the non-separable Coulomb interaction. For near-threshold states, the compositeness can be written solely in terms of the Coulomb scattering length, the Coulomb effective range, and the Bohr radius, providing the weak-binding relation in the presence of the Coulomb interaction. We numerically study the pole trajectories and the compositeness and find that the Coulomb interaction qualitatively modifies the threshold behavior of the poles and the internal structure of the eigenstates. We show that when the Coulomb interaction is relatively strong, the enhancement of the compositeness near the threshold is absent, in contrast to purely short-range interactions. On the other hand, for a weak Coulomb interaction, a remnant of short-range universality survives, and near-threshold bound states tend to be composite dominant. Furthermore, even resonances are dominated by the composite component in the presence of the Coulomb interaction, owing to their continuous connection to the bound-state regime. We apply the formalism to realistic systems with near-threshold eigenstates, including exotic hadrons and nuclei.
Comments:
25 pages, 16 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2604.17813 [pdf]
1 citation
11
[Submitted on 20 Apr 2026] (cross-list from hep-ph)
Jet Quenching in the Smallest Hadronic Collision Systems
Coleridge Faraday🇿🇦 · Ben Bert🇿🇦 · Jack Brand🇿🇦 · Werner Vogelsang🇩🇪 · W. A. Horowitz🇿🇦
We present perturbative quantum chromodynamics (pQCD) predictions for high-momentum particle yield modification in very light ion collisions - $^{10} B +^{10} B$ , $^{6} Li +^{6} Li$ , $^{4} He +^{4} He$ , and $^{3} He +^{3} He$ - with and without medium-induced energy loss. We find non-trivial suppression in symmetric systems from $^{208} Pb +^{208} Pb$ to $^{3} He +^{3} He$ and in asymmetric $A + B$ systems, with the suppression scaling approximately as $R_{A B} ≃ (A B)^{1/3}$ . Further, we find that $^{3} He$ and $^{6} Li$ offer particularly clean environments for observing final-state partonic energy loss from quark-gluon plasma (QGP) formation in extremely small systems. Finally, we show that energy loss models generically predict $v_{2} {SP} \approx 0$ in small systems, indicating that the large measured $v_{2} > 0$ in $p +^{208} Pb$ is not due to energy loss.
Comments:
Contribution to the 2026 QCD session of the 60th Rencontres de Moriond
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2604.18010 [pdf]
0 citations
12
[Submitted on 20 Apr 2026] (cross-list from nucl-ex)
Constraining the trend of the $N = 50$ shell gap towards $^{100}$ Sn with the masses of $^{96 - 98}$ Cd
D. Lange🇩🇪 · D. Atanasov🇧🇪 · M. Au🇨🇭 · A. Belley🇺🇸 · M. Benhatchi🇫🇷 · K. Blaum🇩🇪 · R. B. Cakirli🇩🇪 · P. F. Giesel🇩🇪 · A. Herlert🇩🇪 · J. D. Holt🇨🇦 · B. S. Hu🇺🇸 · A. Jaries🇩🇪 and 15 other authors
We present the first determination of the $N = 50$ empirical shell gap at $Z = 48$ by precise mass measurements of the neutron-deficient cadmium isotopes $^{96 - 98}$ Cd with the ISOLTRAP mass spectrometer at ISOLDE-CERN, including the first precise determination of the excitation energy of the $25/ 2^{+}$ isomer in $^{97}$ Cd. Through the systematics of Coulomb Displacement Energies, we further deduce the empirical shell gap in the higher- $Z$ isotopic chains, tightly constraining the $^{100}$ Sn mass-surface region. The new experimental data suggest an enhancement of the gap towards $^{100}$ Sn, which is discussed in comparison to state-of-the-art calculations using energy-density functional and new ab initio approaches.
Comments:
8 pages, 2 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2604.18287 [pdf]
1 citation

Affiliations

first authorsco-authorsvia INSPIRE