Dashen's theorem and electromagnetic masses of the mesons
  Employing $U(3)_L\times U(3)_R$ chiral field theory, we find that Dashen's theorem, which holds for pseudoscalar mesons, can be generalized to the sector of axial-vector mesons, however, fails for vector mesons. 
Dao-Neng Gao, Mu-Lin Yan and Bing-An Li