2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179211We set up a general framework to describe $ππ$ scattering below 1 GeV based on chiral low-energy expansion with possible spin-0 and 1 resonances. Partial wave amplitudes are obtained with the $N/D$ method, which satisfy unitarity, analyticity and approximate crossing symmetry. Comparison with the phase shift data in the J=0 channel favors a scalar resonance near the $ρ$ mass.17 pages, 5 figures, REVTeXHigh Energy Physics - Phenomenologytext