Nucleon axial form factor at large momentum transfers

TL;DR

This paper provides parameter-free predictions for the nucleon axial form factor at large momentum transfers using a Poincaré-covariant quark+diquark model, analyzing flavor separation and spatial density profiles, with results consistent with experimental data.

Contribution

It introduces a novel, symmetry-preserving, parameter-free calculation of the nucleon axial form factor over a large Q^2 range, including flavor separation and density profiles.

Findings

Predicted axial charge ratio g_A^d/g_A^u = -0.32(2)

D and u quark transverse density profiles are similar

Results align with experimental data on axial form factors

Abstract

Using a Poincar\'e-covariant quark+diquark Faddeev equation and related symmetry-preserving weak interaction current, we deliver parameter-free predictions for the nucleon axialvector form factor, $G_A(Q^2)$, on the domain $0\leq x=Q^2/m_N^2\leq 10$, where $m_N$ is the nucleon mass. We also provide a detailed analysis of the flavour separation of the proton $G_A$ into contributions from valence $u$ and $d$ quarks; and with form factors available on such a large $Q^2$ domain, predictions for the flavour-separated axial-charge light-front transverse spatial density profiles. Our calculated axial charge ratio $g_A^d/g_A^u=-0.32(2)$ is consistent with available experimental data and markedly larger in magnitude than the value typical of nonrelativistic quark models. The value of this ratio is sensitive to the strength of axialvector diquark correlations in the Poincar\'e-covariant nucleon wave function. Working with a realistic axialvector diquark content, the $d$ and $u$ quark transverse density profiles are similar. Some of these predictions could potentially be tested with new data on threshold pion electroproduction from the proton at large $Q^2$.