Resonance sum rules from large $N_C$ and partial wave dispersive   analysis
  Combining large $N_C$ techniques and partial wave dispersion theory to analyze the $\pi\pi$ scattering, without relying on any explicit resonance lagrangian, some interesting results are derived: (a) a general KSRF relation including the scalar meson contribution; (b) a new relation between resonance couplings, with which we have made an intensive analysis in several specific models; (c) low energy constants in chiral perturbation theory related with $\pi\pi$ scattering in terms of the mass and decay width of resonances. 
Zhi-Hui Guo