Masses and widths of the rho(+/-,0)(770)

Isospin violation in the rho (770) mass and width is considered within the S matrix approach using combined fits to the e(+)e(-) --> pi (+)pi (-) and tau (-) --> nu (tau)pi (-)pi (0) data performed by the ALEPH collaboration. We show that the pole position following from the parameters obtained from The ALEPH fits are not sensitive to the derails of the parametrization. In this context, we have found that the pole mass difference and the pole wid th difference between the charged and neutral rho are consistent with zero. We show that a one loop calculation based on Vector Meson Dominance and in cluding vector, axial vector and pseudo-scalar mesons can satisfactorily de scribe the observed isospin breaking. We also give an estimate for the mass difference between the neutral and charged states of the a(1)(1260). (C) 2 001 Published by Elsevier Science B.V.