A possible solution to the gallium anomaly moving beyond the leptonic wave function factorization

TL;DR

This paper revisits the calculation of neutrino capture cross-sections on gallium, moving beyond standard approximations, and suggests that a revised approach could resolve the longstanding gallium anomaly without new physics.

Contribution

It introduces a new method for calculating neutrino capture cross-sections by going beyond the leptonic wave function factorization, potentially explaining the anomaly.

Findings

Revised cross-section can be significantly reduced.

The new approach may resolve the gallium anomaly.

Standard factorization approach has limitations.

Abstract

For over thirty years, a $\sim20\%$ deficit, now exceeding $5\sigma$, has persisted between measured and predicted neutrino capture rates on $^{71}$Ga, as observed in radioactive source experiments (namely GALLEX, SAGE, and more recently BEST) using $^{51}$Cr and $^{37}$Ar. This long-standing discrepancy, referred to as the gallium anomaly, has posed a significant challenge to our understanding of both experimental methods and theoretical predictions. In this work, we revisit the theoretical calculation of the neutrino capture cross-section by moving beyond the standard treatment of the leptonic wave functions, revealing limitations in the commonly used factorization approach based on the detailed balance principle. Incorporating phenomenologically constrained Gamow-Teller transition densities, able to correctly reproduce the precisely measured half-life of $^{71}{\textrm{Ge}}$, we find that the revised cross-section can be significantly reduced, potentially resolving the gallium anomaly without invoking new physics.