Dispersion relation for hadronic light-by-light scattering and the muon g-2
Gilberto Colangelo, Peter Stoffer, Martin Hoferichter, Massimiliano Procura · Proceedings of The 8th International Workshop on Chiral Dynamics — PoS(CD15) · 2016
The largest uncertainties in the Standard Model calculation of the anomalous magnetic moment of the muon (g -2) µ come from hadronic contributions.In particular, it can be expected that in a few years the subleading hadronic light-by-light (HLbL) contribution will dominate the theory uncertainty.We present a dispersive description of the HLbL tensor, which is based on unitarity, analyticity, crossing symmetry, and gauge invariance.Such a model-independent approach opens up an avenue towards a data-driven determination of the HLbL contribution to (g -2) µ .The dispersive approach defines unambiguously the pion-pole and the pion-box contribution to the HLbL tensor.Using Mandelstam's double-spectral representation, we have proven that the pion-box contribution coincides exactly with the one-loop scalar QED amplitude, multiplied by the appropriate pion vector form factors.