Dispersive Approach to Hadronic Light-by-Light

Abstract. A recently proposed dispersive approach to hadronic light-by-light is de-scribed. In this talk I have presented a dispersive approach to hadronic light-by-light (HLbL) which has been recently proposed in [1]. This approach aims to take into account only the cuts in the hadronic tensor which are due to single- or double-pion intermediate states – this approximation is justified by the fact that in explicit calculations higher-lying singularities (like the one due to two kaons) give small contributions [2]. Further, we split the hadronic tensor as follows: Πμνλσ = Π π0−pole μνλσ + Π FsQED μνλσ + Π̄μνλσ + · · · , (1) where the first term takes into account the one-pion pole, the second one two-pion intermediate states with simultaneous cuts in the s and t channel (and all possible cyclic permutations including u), and the third one is the one for which we write down a dispersion relation