Survey of nucleon electromagnetic form factors

TL;DR

This paper reviews the calculation of nucleon electromagnetic form factors using a covariant Faddeev equation framework, highlighting the role of dressed-quarks, diquark correlations, and flavor separation in understanding nucleon structure.

Contribution

It introduces a comprehensive covariant approach to nucleon form factors incorporating diquark correlations and flavor separation, with a single parameter for the diquark charge radius.

Findings

Neutron up-quark radius exceeds down-quark radius due to axial-vector correlations.

Both neutron and proton have a zero in the ratio of Sachs electric to magnetic form factors.

The diquark charge radius parameter aligns with the pion's charge radius.

Abstract

A dressed-quark core contribution to nucleon electromagnetic form factors is calculated. It is defined by the solution of a Poincare' covariant Faddeev equation in which dressed-quarks provide the elementary degree of freedom and correlations between them are expressed via diquarks. The nucleon-photon vertex involves a single parameter; i.e., a diquark charge radius. It is argued to be commensurate with the pion's charge radius. A comprehensive analysis and explanation of the form factors is built upon this foundation. A particular feature of the study is a separation of form factor contributions into those from different diagram types and correlation sectors, and subsequently a flavour separation for each of these. Amongst the extensive body of results that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of axial-vector quark-quark correlations; and for both the neutron and proton the ratio of Sachs electric and magnetic form factors possesses a zero.