2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/202589The hadronic light-by-light contribution to a_{mu}, the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a positive sign for the pion-pole contribution to the hadronic light-by-light correction to a_{mu}, and to a sizeable reduction of the discrepancy between the present experimental value of a_{mu} and its theoretical counterpart in the standard model.4 pages, 1 figure. v2: published versionHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext