Nucleon tensor charges and electric dipole moments

TL;DR

This paper uses a Dyson-Schwinger equation approach to compute nucleon tensor charges and EDM contributions, revealing the impact of diquark correlations and chiral symmetry breaking on nucleon properties.

Contribution

It introduces a symmetry-preserving contact interaction framework to analyze nucleon tensor charges and EDMs, highlighting the role of diquark correlations and chiral symmetry breaking effects.

Findings

Diquark correlations significantly influence nucleon scattering processes.

The ratio of tensor charges $rac{ ext{d}}{ ext{u}}$ is 18% larger than simple models predict.

The size of $ ext{u}$-quark tensor charge is sensitive to chiral symmetry breaking.

Abstract

A symmetry-preserving Dyson-Schwinger equation treatment of a vector-vector contact interaction is used to compute dressed-quark-core contributions to the nucleon $\sigma$-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 $\sigma$-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, $\delta_T u$, $\delta_T d$, the ratio $\delta_T d/\delta_T u$ is 18% larger than anticipated from simple quark models. Of particular note, the size of $\delta_T u$ is a sensitive measure of the strength of dynamical chiral symmetry breaking; and $\delta_T d$ measures the amount of axial-vector diquark correlation within the proton, vanishing if such correlations are absent.