A Dyson-Schwinger equation study of the nucleon-photon vertex.

Diana Nicmorus 
Univ. Graz, Austria

I present a Dyson-Schwinger equation motivated study of the physics 
that governs the nucleon. In particular I focus on the quark-core 
contributions to the nucleon mass and form factors. The calculations 
are performed within in a Poincare-covariant Faddeev framework 
describing the quark-core of the nucleon via a quark-diquark picture.  
A consistent setup for the dressed-quark propagator, the quark-quark 
and the quark-diquark interactions is used, where all the ingredients 
are solutions of their respective Dyson-Schwinger or Bethe-Salpeter 
equations and obtained in the rainbow-ladder truncation. In the 
quark-diquark picture a nucleon-photon vertex that fulfills the 
electromagnetic Ward-Takahashi identity is resolved by specifying 
the quark-photon and diquark-photon vertices, and by using a 
consistent ansatz for the seagull terms. I discuss the evolution of 
the nucleon properties with the current quark mass, as well as the 
role of the pion cloud in this approach. I also present a comparison 
of the results to a collection of experimental and lattice data.