2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179051We evaluate analytically the elastic $ππ$ scattering amplitude to two loops in chiral perturbation theory and give numerical values for the two $S$--wave scattering lengths and for the phase shift difference $δ_0^0-δ_1^1$.10 pages, LaTeX, uses epsfig.sty, one postscript picture included. Full postscript file available at http/www.nordita.dk/locinfo/preprints/95077.ps.gzHigh Energy Physics - PhenomenologyNuclear Theorytext