Pion and Kaon Vector Form Factors: a Chiral Unitary Approach
  The pion and kaon coupled-channel vector form factors are described by making use of the resonance chiral Lagrangian results together with a suitable unitarization method in order to take care of the final state interactions. A very good reproduction of experimental data is accomplished for the vector form factors up to $\sqrt{s}\leq 1.2$ GeV and for the $\pi\pi$ P-wave phase shifts up to $\sqrt{s}\leq 1.5$ GeV. 
J.E. Palomar, J.A. Oller and E. Oset