Heavy-Meson Decay Constants: Isospin Breaking from QCD Sum Rules
  Compared with lattice QCD, isospin breaking of heavy-meson decay constants from QCD sum rules agrees for $D$ mesons but disagrees (by a factor of four) for $B$ mesons. 
Wolfgang Lucha, Dmitri Melikhov, Silvano Simula
hep-ph hep-lat nucl-th