Ab-initio electroweak corrections to superallowed $\beta$ decays and their impact on $V_{ud}$

TL;DR

This paper develops an effective field theory framework to accurately compute electroweak radiative corrections in superallowed beta decays, reducing uncertainties in the determination of the CKM matrix element V_{ud} using ab-initio nuclear methods.

Contribution

It introduces a systematic EFT approach to calculate nucleus-dependent electroweak corrections and evaluates dominant effects in light nuclei with Quantum Monte Carlo methods.

Findings

Confirmed EFT power counting predictions for light nuclei corrections.

Provided numerical estimates for dominant electroweak corrections in specific nuclei.

Discussed methods to extract low-energy constants from experimental data.

Abstract

Radiative corrections are essential for an accurate determination of $V_{ud}$ from superallowed $\beta$ decays. In view of recent progress in the single-nucleon sector, the uncertainty is dominated by the theoretical description of nucleus-dependent effects, limiting the precision that can currently be achieved for $V_{ud}$. In this work, we provide a detailed account of the electroweak corrections to superallowed $\beta$ decays in effective field theory (EFT), including the power counting, potential and ultrasoft contributions, and factorization in the decay rate. We present a first numerical evaluation of the dominant corrections in light nuclei based on Quantum Monte Carlo methods, confirming the expectations from the EFT power counting. Finally, we discuss strategies how to extract from data the low-energy constants that parameterize short-distance contributions and whose values are not predicted by the EFT. Combined with advances in ab-initio nuclear-structure calculations, this EFT framework allows one to systematically address the dominant uncertainty in $V_{ud}$, as illustrated in detail for the $^{14}$O $\to$ $^{14}$N transition.