Longitudinal Transitions Of Baryon Resonances in Constituent Quark Model
  A longitudinal transition operator that satisfies the gauge invariance requirement is introduced in constituent quark model. The corresponding longitudinal transitions between the nucleon and baryon resonances are calculated. We show that the study of the longitudinal coupling plays an important role in understanding the structure of baryons. 
Zhenping Li, Yubing Dong and Weihsing Ma