Resummation Study on Decay rhotoππ in U(2)_Ltimes U(2)_R Chiral Theory of Mesons

We improve $O(p^4)$ calculation in $U(2)_L\times U(2)_R$ chiral theory of mesons by resummation calculation for vector mesons physics and restudy decay $\rho\to\pi\pi$. A complete and compact expression for $f_{\rho\pi\pi}(p^2)$ (up to $O(p^\infty)$) is obtained, from which an important non-perturbative conclusion is given based on convergence and unitarity consideration.