${\rho }^0-\omega$ mixing in U(3)}${}_L\times$ U(3)${}_R$ chiral theory of mesons

In this paper, U(3)${}_L\times$ U(3)${}_R$ chiral theory of mesons is extended to the leading order in quark mass expansion in order to evaluate the ${\rho }^0-\omega$ mixing. It is shown that the use of path integral method to integrate out the quark fields naturally leads to the ${\rho }^0-\omega$ mixing vertices, and this mixing is entirely from the quark loop in this theory. The off-shell behaviour of the mixing amplitude is analyzed. The on-shell mixing amplitude is obtained from the decay $\omega \to {\pi }^{+}{\pi }^{-}$. Furthermore, the constraints on the light quark mass parameters are extracted from the ${\rho }^0-\omega$ mixing and the mesons masses, and the mass splitting of $K^{\ast }(892)$-mesons is predicted.