THE CHIRAL LAGRANGIAN PARAMETERS, (L)OVER-BAR(1), (L)OVER-BAR(2), AREDETERMINED BY THE RHO-RESONANCE

The all-important consequence of Chiral Dynamics for pi pi scattering is the Adler zero, which forces pi pi amplitudes to grow asymptoticall y. The continuation of this subthreshold zero into the physical region s requires a P-wave resonance, to be identified with the rho. It is a feature of pi pi scattering that convergent dispersive integrals for t he I = 1 channel are essentially saturated by the rho-resonance and ar e much larger than those with I = 2 quantum numbers. These facts predi ct the parameters ($) over bar l(1), ($) over bar l(2) of the Gasser-L eutwyler Chiral Lagrangian, as well as reproducing the well-known KSFR relation and self-consistently generating the rho-resonance.