Analysis of rho-omega interference in the pion form-factor
  The formalism underlying the analysis of e+e- -> pi+pi- in the rho-omega interference region is carefully revisited. We show that the standard neglect of the pure I=0 omega, omega_I, `direct'' coupling to pi-pi is not valid, and extract those combinations of the direct coupling and \rho-omega mixing allowed by experiment. The latter is shown to be only very weakly constrained by experiment, and we conclude that data from the e+e- -> pi+pi- interference region cannot be used to fix the value of rho-omega mixing in a model-independent way unless the errors on the experimental phase can be significantly reduced. Certain other modifications of the usual formalism necessitated by the unavoidable momentum-dependence of rho-omega mixing are also discussed. 
K. Maltman, H.B. O'Connell and A.G. Williams