The 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.Comment: 4 pages, 1 figure. v2: published versio
