QED penguin contributions to isospin splittings of heavy-light quark systems

Recent experiments show that the isospin-violating mass splitting of the B mesons is very small, but the best fits with a QCD sum rule analysis give a splitting of at least 1.0 MeV. The isospin-violating mass splittings of the charmed mesons, on the other hand, are in agreement with experiment. In this letter we show that the inclusion of 2nd kind QED penguin diagrams can account for this discrepancy within the errors in the QCD sum rule method.