June 29, 2015 to July 3, 2015
Europe/Rome timezone

Dispersion relation for hadronic light-by-light scattering and the muon (g-2)

Jul 2, 2015, 3:20 PM
Aula Magna (Building E, Polo Fibonacci, Pisa)

Aula Magna

Building E, Polo Fibonacci, Pisa

Talk Goldstone Boson Working Group Parallel Session 5 - Goldstone Boson WG


Peter Stoffer (HISKP, University of Bonn)


The anomalous magnetic moment of the muon (g −2)µ has been measured and computed to very high precision of about 0.5 ppm. For more than a decade, a discrepancy has persisted between experiment and Standard Model prediction, now of about 3σ. The main uncertainty of the theory prediction is due to strong interaction effects. With the expected improvement of the input for hadronic vacuum polarisation, in a few years the subleading hadronic light-by-light (HLbL) contribution will dominate the theory error. While some constraints from QCD exist, the calculation of the HLbL contribution to the (g − 2)µ is plagued by a substantial model dependence. In this talk, I will present a dispersive approach to HLbL scattering, based on the fundamental principles of unitarity and analyticity [1] We have derived a Lorentz decomposition of the HLbL tensor that is fully gauge-invariant and crossing symmetric [2,3]. The scalar coefficient functions of this tensor decomposition are free of kinematic singularities and zeros and fulfil Mandelstam’s double-dispersive representation. The dispersive formalism defines unambiguously and in a model-independent way both the pion-pole and the pion-loop contribution. Two-pion rescattering effects are included in a partial-wave picture. Our dispersive formalism shows a path towards a data-driven determination of the HLbL contribution to the (g − 2)µ [4]. References 1. G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, JHEP 1409, 091 (2014),[arXiv:1402.7081 [hep-ph]]. 2. G. Colangelo, M. Hoferichter, M. Procura, and P. Stoffer, in preparation. 3. P. Stoffer, PhD thesis, University of Bern, 2014, arXiv:1412.5171 [hep-ph]. 4. G. Colangelo, M. Hoferichter, B. Kubis, M. Procura, and P. Stoffer, Phys. Lett. B738, 6 (2014), [arXiv:1408.2517 [hep-ph]].

Primary author

Peter Stoffer (HISKP, University of Bonn)


Prof. Gilberto Colangelo (Berna University) Dr Martin Hoferichter (TU Darmstadt) Dr Massimiliano Procura (University of Vienna)

Presentation materials