Isospin splittings in baryons with two heavy quarks

Isospin splittings in baryons with two heavy quarks and a u or d quark are calculated using simple methods proposed previously by the authors. The results are M(Xi(++)(cc)) - M(Xi(+)(cc)) = 1.41 +/- 0.12(+0.76) MeV, M(Xi(0)(bb)) - M(Xi(-)(bb)) = -4.78 +/- 0.06(+0.03) MeV, and M(Xi(+)(bc)) - M(Xi(0)(bc)) = -1.69 +/- 0.07(+0.39) MeV,where the statistical errors reflect uncertainties in input mass splittings, and the systematic errors are associated with the choice of constituent-quark masses.