Further remarks on $\pi \pi$ scattering dispersion relations

The naive use of higher order perturbation theory leads the left–hand cut integrals in $\pi \pi$ dispersion relations~\cite{hjy,Xiao01} divergent. This problem is discussed and solved. Also we point out that the Adler zero condition imposes three constraints on the dispersion relations. The $\sigma$ pole position is determined using the improved method, $M_\sigma= 483\pm 13 {\rm MeV}$,$\Gamma_\sigma= 705 \pm 50{\rm MeV}$. The scattering length parameter is found to be in excellent agreement with the experimental result.