Nucleon axial form factor at large momentum transfers

Abstract

Using a Poincaré-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 0le x=Q^2/m_N^2le 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 Poincaré-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.