The muon g-2: Dyson-Schwinger status on hadronic light-by-light   scattering
  We give a status report on the hadronic light-by-light scattering contribution to the muon's anomalous magnetic moment from the Dyson-Schwinger approach. We discuss novel, model-independent properties of the light-by-light amplitude: we give its covariant decomposition in view of electromagnetic gauge invariance and Bose symmetry, and we identify the relevant kinematic regions that are probed under the integral. The decomposition of the amplitude at the quark level and the importance of its various diagrams are discussed and related to model approaches. 
Gernot Eichmann, Christian S. Fischer, Walter Heupel, Richard Williams
hep-ph hep-lat nucl-th