2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/103422The scalar-isoscalar, scalar-isotensor and vector-isovector pi-pi amplitudes have been fitted simultaneously to experimental data and to to Roy's equations. Resulting pi-pi phase shifts up to 1600 MeV and near threshold observables have been analyzed. Only the amplitudes fitted to the "down-flat" set of phase shifts in scalar-isoscalar wave fulfill crossing symmetry conditions and can be regarded as physical.4 pages, talk presented at 12th International QCD Conference (QCD05) 4-9th July 2005 Montpellier (France), to appear in Nucl. Phys. B (Proc. Suppl.)High Energy Physics - Phenomenologytext