2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/214773We consider the hadronic description of the $B^0_d\to π^+π^-$ decay, with the aim to investigate the strong phases generated by the final state interactions. The derivation of the dispersion relations using the Lehmann-Symanzik-Zimmermann formalism and the Goldberger-Treiman method to include inelastic effects in the spectral function are presented. We discuss the problem of quark-hadron duality and estimate in the hadronic formalism the corrections to the factorized amplitude in the heavy quark limit.16 pages, revised version, introduction of a scale dependenceHigh Energy Physics - Phenomenologytext