ϱ0 - ω mixing in chiral perturbation theory

In order to calculate the ϱ0 - ω mixing we extend the chiral couplings of the low-lying vector mesons in chiral perturbation theory to a lagrangian that contains two vector fields. We determine the two-point function and recover an earlier result for the mixing amplitude. We give an update of the quark mass ratio R = (ms − m)(md − mu).