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The quadratic pion scalar radius, \la r^2\ra^\pi_s, plays an important rolefor present precise determinations of \pi\pi scattering. Recently, Yndur\'ain,using an Omn\`es representation of the null isospin(I) non-strange pion scalarform factor, obtains \la r^2\ra^\pi_s=0.75\pm 0.07 fm^2. This value is largerthan the one calculated by solving the corresponding Muskhelishvili-Omn\`esequations, \la r^2\ra^\pi_s=0.61\pm 0.04 fm^2. A large discrepancy between bothvalues, given the precision, then results. We reanalyze Yndur\'ain's method andshow that by imposing continuity of the resulting pion scalar form factor undertiny changes in the input \pi\pi phase shifts, a zero in the form factor forsome S-wave I=0 T-matrices is then required. Once this is accounted for, theresulting value is \la r^2\ra_s^\pi=0.65\pm 0.05 fm^2. The main source of errorin our determination is present experimental uncertainties in low energy S-waveI=0 \pi\pi phase shifts. Another important contribution to our error is the notyet settled asymptotic behaviour of the phase of the scalar form factor fromQCD.

Scalar radius of the pion and zeros in the form factor