Radiative corrections to nucleon weak charges and Beyond Standard Model impact

TL;DR

This paper presents a comprehensive calculation of electroweak radiative corrections to the nucleon axial charge, refining its value and implications for Standard Model tests and beyond, including constraints on new physics.

Contribution

It provides the first complete $ ext{O}( ext{α})$ electroweak correction calculation for the nucleon axial charge using current algebra and QCD sum rules, improving precision and consistency.

Findings

Enhanced weak magnetism contribution in elastic channel.

New value for the axial charge $g_A^0 = 1.2730(13)$ with >2σ shift.

Constraints on exotic right-handed currents from lattice QCD.

Abstract

The nucleon axial charge is a central ingredient in nuclear and particle physics, and a key observable in precision tests of the electroweak Standard Model sector and beyond. We report on the first complete calculation of its electroweak quantum corrections up to $\mathcal{O}(\alpha)$, using a combination of current algebra techniques and QCD sum rules. We find a substantial enhancement due to the weak magnetism contribution in the elastic channel, and include higher-twist and target mass corrections at low $Q^2$ to find $\Delta_R^A = 0.02881(22)$. Using analogous methods, we determine a new value for the vector charge renormalization, $\Delta_R^V = 0.02474(27)$, and show how the two most recent calculations can be brought into agreement. This allows us to determine a corrected experimental $g_A^0 = 1.2730(13)$, which is a $>2\sigma$ shift away from the commonly quoted value. We use this new result to set constraints on exotic right-handed currents by comparing to lattice QCD results, and resolve a double-counting issue in the $|V_{ud}|$ extraction from mirror decays.