%0 Journal Article
%A Hoferichter, Martin
%A Colangelo, Gilberto
%A Hoid, Bai-Long
%A Kubis, Bastian
%A Ruiz De Elvira Carrascal, Jacobo
%A Schuh, Dominic
%A Stamen, Dominik
%A Stoffer, Pete
%T Phenomenological estimate of isospin breaking in hadronic vacuum polarization
%D 2023
%@ 0031-9007
%U https://hdl.handle.net/20.500.14352/102585
%X Puzzles in the determination of the hadronic-vacuum-polarization contribution currently impede a conclusive interpretation of the precision measurement of the anomalous magnetic moment of the muon at the Fermilab experiment. One such puzzle concerns tensions between evaluations in lattice QCD and using e+e- -> hadrons cross-section data. In lattice QCD, the dominant isospin-symmetric part and isospin-breaking (IB) corrections are calculated separately, with very different systematic effects. Identifying these two pieces in a data-driven approach provides an opportunity to compare them individually and trace back the source of the discrepancy. Here, we estimate the IB component of the lattice-QCD calculations from phenomenology, based on a comprehensive study of exclusive contributions that can be enhanced via infrared singularities, threshold effects, or hadronic resonances, including, for the first time, in the e+e- -> 3 pi channel. We observe sizable cancellations among different channels, with a sum that even suggests a slightly larger result for the QED correction than obtained in lattice QCD. We conclude that the tensions between lattice QCD and e+e- data therefore cannot be explained by the IB contributions in the lattice-QCD calculations.
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