Masses and widths of the rho(770)

Isospin violation in the $\rho(770)$ mass and width is considered within the $S$ matrix approach using combined fits to the $e^+e^- \to\pi^+\pi^-$ and $\tau^- \to \nu_{\tau}\pi^-\pi^0$ 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 details of the parametrization. In this context, we have found that the pole mass difference and the pole width difference between the charged and neutral $\rho$ are consistent with zero. We show that a one loop calculation including vector, axial vector and pseudo-scalar mesons can satisfactorily describe the observed isospin breaking. We also give an estimate for the mass difference between the neutral and charged states of the $a_1(1260)$.Comment: 8 pages, 1 figur

Pion Scattering Revisited

Chiral Ward identities lead to consistent accounting for the sigma's width in the linear sigma model's Feynman rules. Reanalysis of pion scattering data at threshold imply a mass for the sigma of 600+ 200 - 100 MeV.Comment: latex; VIII EMPC (Oaxaca, Nov 98) Proceeding

Tests of flavor symmetry in J/psi decays

We use SU(3) flavor symmetry to analyze the $PP', VP$ and baryon-antibaryon decays of $J/\psi$. Both, the SU(3)-invariant and -violating contributions are considered. Particular attention is paid to the interference of the electromagnetic and strong amplitudes.Comment: 8 pages, latex. Talk given at CAM-94 Physics Meetin