Dispersive approach to hadronic light-by-light scattering and the muon ɡ − 2 Peter Stoffer, Gilberto Colangelo, Martin Hoferichter and Massimiliano Procura EPJ Web of Conferences, 81 (2014) 05026 Published online: 26 November 2014 DOI: 10.1051/epjconf/20148105026