Evaluation of the derivative quartic terms of the meson chiral Lagrangian from forward dispersion relations

Using the forward dispersion relations for {π}{π} scattering, we show that the coefficients of the derivative quartic terms in the chiral Lagrangian are positive. The Skyrme term is mainly given by the {ρ}-meson contribution to the I=1 total cross section and gives a proton mass of 1.27 GeV. The non-Skyrme term is found of comparable strength from the I=0 S-wave {π}{π} data.