In my talk, I will present a data-driven coupled-channel analysis of the isoscalar S-wave $\pi\pi/KK$ scattering using partial-wave dispersion relations. The central result is the Omnes matrix, which has only right-hand cuts, making it a crucial input for studying the final state interactions of any hadron processes involving a system of two pions (and two kaons). As an application, I will showcase our recent findings on $ee \to J/\psi\pi\pi(KK)$ and $\gamma*\gamma* \to \pi\pi/KK$ scattering. The results from $\gamma*\gamma* \to \pi\pi/KK$ allowed us to perform a dispersive estimation of the contributions of the $f_0(500)$ and $f_0(980)$ resonances to $(g-2)_\mu$.
IFIC seminar organizers