Form factors of the nucleon axial current

A symmetry-preserving Poincare-covariant quark+diquark Faddeev equation treatment of the nucleon is used to deliver parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors, G(A) and G(P), respectively. The result for G(A) can reliably be represented by a dipole form factor characterised by an axial charge g(A) = G(A)(0) = 1.25(3) and a mass-scale M-A = 1.23(3)m(N), where m(N) is the nucleon mass; and regarding GP, the induced pseudoscalar charge g*(p) = 8.80(23), the ratio g*(p)/g(A) = 7.04(22), and the pion pole dominance Ansatzis found to provide a reliable estimate of the directly computed result. The ratio of flavour-separated quark axial charges is also calculated: g(A)(d)/g(A)(u) = -0.16(2). This value expresses a marked suppression of the size of the d-quark component relative to that found in nonrelativistic quark models and owes to the presence of strong diquark correlations in the nucleon Faddeev wave function - both scalar and axial-vector, with the scalar diquark being dominant. The predicted form for G(A) should provide a sound foundation for analyses of the neutrino-nucleus and antineutrino-nucleus cross-sections that are relevant to modern accelerator neutrino experiments. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The parameter-free predictions for the nucleon's axial and induced pseudoscalar form factors have been obtained using a symmetry-preserving Poincare-covariant quark+diquark Faddeev equation treatment. The results provide reliable estimates for the axial and pseudoscalar charges, as well as insights into the flavour-separated quark axial charges and the impact of strong diquark correlations in the nucleon Faddeev wave function, laying a solid foundation for analyses of neutrino-nucleus and antineutrino-nucleus cross-sections relevant to modern accelerator neutrino experiments.