Speaker
Description
The Gallium Anomaly, a persistent discrepancy exceeding 5$\sigma$ between measured and predicted neutrino capture rates on $^{71}$Ga from $^{51}$Cr and $^{37}$Ar radioactive sources (GALLEX, SAGE, and BEST), has challenged particle physics for over three decades. This deficit has widely been interpreted as a possible signature of short-baseline oscillations involving eV-scale sterile neutrinos. In this work, we present a comprehensive reevaluation of the neutrino capture cross-section on $^{71}$Ga, abandoning conventional leading-order approximations. We employ a new calculation framework that numerically solves the Dirac-Coulomb equation for both bound and continuum electron states, providing a precise treatment of the leptonic wave functions. First, we analyze the anomaly under the standard nuclear structure hypothesis, where the Gamow-Teller transition density is approximated by the charge density distribution. Within this framework, we update the global significance of the anomaly and present the most up-to-date constraints on the $3+1$ sterile neutrino mixing parameters. While this refined calculation modifies the tension, the discrepancy remains statistically significant under these standard assumptions [1, 1a].
Subsequently, we critically examine the validity of the factorization approach based on the detailed balance principle. We demonstrate that the approximation of the transition density with the charge density is insufficient to capture the nuclear dynamics. By incorporating phenomenologically constrained Gamow-Teller transition densities, which are tuned to correctly reproduce the precisely measured half-life of $^{71}$Ge, we find that the theoretical cross-section is significantly reduced compared to standard predictions. We show that this reduction in the cross-section can fully accommodate the experimental data from GALLEX, SAGE, and BEST. Consequently, the Gallium Anomaly can be potentially resolved without invoking new physics [2]. This result eliminates the necessity for eV-scale sterile neutrinos to explain the gallium data, thereby reinforcing the consistency of the current global neutrino landscape and aligning with the recent null results from KATRIN and MicroBooNE.
We conclude by assessing the impact of the modified capture rates on Gallium on the global analysis of solar neutrino data and the resulting oscillation parameters [3].
Based on:
[1] M. Cadeddu, N. Cargioli, G. Carotenuto, F. Dordei, L. Ferro, C. Giunti, arXiv:2507.13103, Reassessing the gallium anomaly using self-consistent electron wave functions, PRD https://doi.org/10.1103/pz8g-zz1b
[1a] M. Cadeddu @ XXI Internation Workshop on Neutrino Telescopes 2025, Padova, The Gallium Anomaly, https://agenda.infn.it/event/44606/contributions/269094/
https://agenda.infn.it/event/44606/contributions/269094/attachments/140693/216348/Gallium_Anomaly_Cadeddu_Matteo_FINAL.pdf
[2] M. Cadeddu, N. Cargioli, F. Dordei, L. Ferro, C. Giunti, M. Pitzalis, arXiv:2512.20560, A possible solution to the gallium anomaly moving beyond the leptonic wave function factorization, Under review.
[3] M. Cadeddu et al., In preparation.