Isospin mass differences of the B , D and K

bstract We compute the electromagnetic mass difference for the B -, D - and K -mesons using QCD sum rules with double dispersion relations. For the B - and D -mesons we also compute the linear quark mass correction, whereas for the K the standard soft theorems prove more powerful. The mass differences, which have not previously been computed via a double dispersion, are fully consistent with experiment, albeit with large uncertainties.