The axial coupling of the nucleon, gA = 1.2723(23), is the strength of the nucleon's coupling to the weak axial current of the Standard Model. It dictates the rate at which neutrons decay into protons, the strength of the attractive long-range force between nucleons, and other features of nuclear physics. To disentangle Standard Model effects from new physics, precision tests of the Standard Model in nuclear environments require a quantitative understanding of nuclear physics rooted in QCD, the theory of quarks and gluons. The nucleon axial coupling has long been considered a critical benchmark for lattice QCD, and yet proved substantially more challenging to calculate than expected. I will describe and give an update to our recent percent-level calculation, gA = 1.271(13), and how our method differs from existing approaches.
[1] C.C. Chang et al., "A per-cent-level determination of the nucleon axial coupling from Quantum Chromodynamics", Nature, 558:91-94, DOI:10.1038/s41586-018-0161-8 arXiv:1805.12130.
