Nuclear Theory·nucl-th

Monday·April 21, 2025

6 papers—3 primary·3 cross-listed

04
[Submitted on 17 Apr 2025] (cross-list from nucl-th)
The Unitarity-Limit Expansion for Two Nucleons with Perturbative Pions: Digest and Ideas
Harald W. Griesshammer (George Washington U.)🇺🇸
In the Unitarity Limit, the NN S-wave binding energies are zero, the scattering lengths infinite, Physics is universal, i.e. insensitive to details of the interactions, and observables display richer symmetries, namely invariance under both scaling and Wigner's combined SU(4) transformation of spin and isospin. This presentation is a digest of the first quantitative exploration of corrections to this picture when pions are included [1] (see there for a more comprehensive list of references). Since the pion mass and decay constant introduce dimensionful scales in the NN system, they explicitly break the symmetries of the Unitarity fixed point. In $χ$ EFT, these symmetries must therefore be classified as emergent. This text focuses on the $χ$ EFT variant with Perturbative ("KSW") Pions at next-to-next-to leading order (N2LO). This leads to the Hypothesis that both scale invariance and Wigner-SU(4) symmetry in the Unitarity Expansion show persistence, i.e. the footprint of both combined dominates even for $k ≳ m_{π}$ and is more relevant than chiral symmetry, so that the tensor/Wigner-SU(4) symmetry-breaking part of OPE is suppressed and does not enter before N3LO. Included are also ideas about underlying mechanisms and LO results of $χ$ EFT with Nonperturbative Pions in the expansion about Unitarity.
Comments:
10 pages LaTeX2e (pdflatex) in pos.sty including 7 figures as 9 .pdf files using includegraphics. Minor typographical corrections
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Atomic Physics (physics.atom-ph)
arXiv:
2504.13353 [pdf]
PoS(2026)·2 citations
05
[Submitted on 18 Apr 2025] (cross-list from astro-ph.SR)
The impact of new ( $α$ , n) reaction rates on the weak s-process in metal-poor massive stars
Wenyu Xin · Chun-Ming Yip · Ken'ichi Nomoto · Xianfei Zhang · Shaolan Bi
Massive stars are significant sites for the weak s-process (ws-process). $^{22}$ Ne and $^{16}$ O are, respectively, the main neutron source and poison for the ws-process. In the metal-poor stars, the abundance of $^{22}$ Ne is limited by the metallicity, so that the contribution of $^{22}$ Ne( $α$ , n) $^{25}$ Mg reaction on the s-process is weaker. Conversely, the $^{17}$ O( $α$ , n) $^{20}$ Ne reaction becomes more prominent in these stars due to the most abundant $^{16}$ O in all metallicities. In this work, we calculate the evolution of four metal-poor models ( $Z = 1 0^{- 3}$ ) for the Zero-Age Main-Sequence (ZAMS) masses of $M (ZAMS) =$ 15, 20, 25, and 30 M $_{⊙}$ to investigate the effect of reaction rates on the ws-process. We adopt the new $^{17}$ O( $α$ , n) $^{20}$ Ne and $^{17}$ O( $α, γ$ ) $^{21}$ Ne reaction rates suggested by Best et al. (2013) and $^{22}$ Ne( $α$ , n) $^{25}$ Mg and $^{22}$ Ne( $α, γ$ ) $^{26}$ Mg from Wiescher et al. (2023). The yields of the s-process isotope with updated reaction rates are compared with the results using default reaction rates from JINA REACLIB. We find that the new $^{17}$ O+ $α$ reaction rates increase the ws-process mainly in all the stages, while the new $^{22}$ Ne+ $α$ reaction rates only increase the ws-process in C and Ne burning stages. Updating these new reaction rates would increase the production of ws-process isotopes by tens of times. We also note that for more massive stars, the enhancement by new $^{17}$ O+ $α$ reaction rates become more significant.
Comments:
16 pages, 15 figures
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2504.13766 [pdf]
Nucl.Sci.Tech.(2026)·1 citation
06
[Submitted on 18 Apr 2025] (cross-list from hep-ph)
Extracting the chiral anomaly from $e^{+} e^{-} \to 3 π$
Martin Hoferichter🇨🇭 · Bai-Long Hoid🇩🇪 · Bastian Kubis🇩🇪
The strength of the interaction of three pions and a photon, $F_{3 π}$ is predicted by the axial anomaly in terms of the pion decay constant, a relation that is frequently used to constrain low-energy radiative processes involving pions, but only tested experimentally at the $10%$ level. Here, we present a new avenue to test this prediction, via a fit of a dispersive description of the $γ^{*} \to 3 π$ amplitude to data for $e^{+} e^{-} \to 3 π$ . From the global fit to SND, CMD-2, and BaBar data we obtain $F_{3 π} = 33.1 (1.7) GeV^{- 3}$ , in agreement with the chiral prediction at the level of $5%$ . We also consider dispersive fits to the recent data by Belle II, in which case we observe tensions with the dispersive constraints, the width parameters of $ω$ and $ϕ$ , and the chiral anomaly.
Comments:
17 pages, 1 figure; journal version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
2504.13827 [pdf]
JHEP(2025)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE

The Unitarity-Limit Expansion for Two Nucleons with Perturbative Pions: Digest and Ideas

The impact of new (α, n) reaction rates on the weak s-process in metal-poor massive stars

Extracting the chiral anomaly from e+e−→3π

Affiliations

The impact of new ( $α$ , n) reaction rates on the weak s-process in metal-poor massive stars

Extracting the chiral anomaly from $e^{+} e^{-} \to 3 π$