Chiral coupling constants ${\overline{l}}_1$ and ${\overline{l}}_2$ from $\pi \pi$ phase shifts

A Roy equation analysis of the available $\pi \pi$ phase shift data is performed with the $I=0\mathrm{}$ $S$-wave scattering length $a_0^0$ in the range predicted by the one-loop standard chiral perturbation theory. A suitable dispersive framework is developed to extract the chiral coupling constants ${\overline{l}}_1$, ${\overline{l}}_2$ and yields ${\overline{l}}_1=1.70\mathrm{}\pm 0.15$ and ${\overline{l}}_2\approx 5.0$. We remark on the implications of this determination to (combinations of) threshold parameter predictions of the three lowest partial waves.