Nucleon axial and pseudoscalar form factors using twisted-mass fermion ensembles at the physical point

Abstract

We compute the nucleon axial and pseudoscalar form factors using three Nf=2+1+1 twisted-mass fermion ensembles with all quark masses tuned to approximately their physical values. The values of the lattice spacings of these three physical point ensembles are 0.080, 0.068, and 0.057 fm and spatial sizes 5.1, 5.44, and 5.47 fm, respectively, yielding mπL>3.6. Convergence to the ground-state matrix elements is assessed using multistate fits. We study the momentum dependence of the three form factors and check the partially conserved axial-vector current (PCAC) hypothesis and the pion pole dominance (PPD). We show that in the continuum limit, the PCAC and PPD relations are satisfied. We also show that the Goldberger-Treimann relation is approximately fulfilled and determine the Goldberger-Treiman discrepancy. Our final results are gA=1.245(28)(14) for the nucleon axial charge, ⟨rA2⟩=0.339(48)(06)fm2 for the axial radius, gπNN≡limQ2→−mπ2GπNN(Q2)=13.25(67)(69) for the pion-nucleon coupling constant, and GP(0.88mμ2)≡gP*=8.99(39)(49) for the induced pseudoscalar form factor at the muon capture point. Published by the American Physical Society 2024