The Muon Anomalous Magnetic Moment and the Pion Polarizability

We compute the charged pion loop contribution to the muon anomalous magnetic moment ɑ_µ, taking into account the effect of the charged pion polarizability, (ɑ_1 - β_1)_π^+. We evaluate this contribution using two different models that are consistent with the requirements of chiral symmetry in the low-momentum regime and perturbative quantum chromodynamics in the asymptotic region. The result increases the disagreement between the present experimental value for ɑ_µ and the theoretical, Standard Model prediction by as much as ~ 60 x 10^(-11), depending on the value of (ɑ_1 - β_1)_π^+ and the choice of the model. The planned determination of (ɑ_1 - β_1)_π^+ at Jefferson Laboratory will eliminate the dominant parametric error, leaving a theoretical model uncertainty commensurate with the error expected from planned Fermilab measurement of a_µ.