The strange and flavor-singlet axial form factors of the nucleon from lattice QCD

TL;DR

This paper presents a comprehensive lattice QCD study of the nucleon’s flavor-separated axial form factors, including the crucial strange quark contribution, with a focus on disconnected diagrams and systematic uncertainties.

Contribution

It provides the first full error budget and a detailed lattice QCD determination of the nucleon axial form factors across all flavor channels, emphasizing the strange component.

Findings

Successful extraction of the strange axial form factor $G^{s}_A(Q^2)$

Quantitative flavor decomposition of the nucleon spin structure

Systematic control over chiral, continuum, and volume extrapolations

Abstract

The singlet axial form factor of the nucleon provides essential input for a complete understanding of the nucleon axial structure. Together with the isovector and isoscalar octet channels, in the forward limit it forms the basis for a full flavor decomposition of the proton spin. In this work we present a lattice QCD determination of the singlet axial form factor $G^{u+d+s}_A(Q^2)$ and related strange contribution $G^{s}_A(Q^2)$ using a set of $N_f = 2 + 1$ CLS gauge ensembles with $O(a)$-improved Wilson fermions, with a full error budget for the extrapolation to the chiral, continuum and infinite-volume limits. Particular focus is placed on the treatment of the disconnected contributions, which constitute the crucial element for the extraction of the strange component. Together with determinations of the isovector and isoscalar octet axial form factors, this work provides a comprehensive lattice QCD determination of the nucleon axial structure across different flavor channels.