Model-independent Study of Electric Dipole Transitions in Quarkonium
  The paper contains a systematic, model-independent treatment of electric dipole (E1) transitions in heavy quarkonium. Within the effective field theory framework of potential non-relativistic QCD (pNRQCD), we derive the complete set of relativistic corrections of relative order v^2 both for weakly and strongly-coupled quarkonia. The result supports and complements former results from potential model calculations. 
Nora Brambilla, Piotr Pietrulewicz, Antonio Vairo
hep-ph