Nucleon tensor charges and electric dipole moments
A symmetry-preserving Dyson-Schwinger equation treatment of a vector-vector contact interaction is used to compute dressed-quark-core contributions to the nucleon σ-term and tensor charges. The latter enable one to directly determine the effect of dressed-quark electric dipole moments (EDMs) on neutron and proton EDMs. The presence of strong scalar and axial-vector diquark correlations within ground-state baryons is a prediction of this approach. These correlations are active participants in all scattering events and thereby modify the contribution of the singly represented valence quark relative to that of the doubly represented quark. Regarding the proton σ-term and that part of the proton mass which owes to explicit chiral symmetry breaking, with a realistic d-u mass splitting, the singly represented d quark contributes 37% more than the doubly represented u quark; and in connection with the proton’s tensor charges, δTu, δTd, the ratio δTd/δTu is 18% larger than anticipated from simple quark models. Of particular note, the size of δTu is a sensitive measure of the strength of dynamical chiral symmetry breaking; and δTd measures the amount of axial-vector diquark correlation within the proton, vanishing if such correlations are absent.