UNIFIED DISPERSIVE APPROACH TO γ* → γππ AND γγ → ππ

Abstract

A representation of the amplitude γ*(q2) → γππ is proposed which combines large Nc chiral resonance Lagrangian modelling with general unitarity and analyticity properties. The amplitude is constrained from γγ scattering results and e+e− → γπ0π0 measurements by the CMD-2 and SND collaborations. As an application, the contribution of the ππ + γ states in the HVP contribution to the muon g - 2 are reconsidered, taking into account the effect of the strong S-wave ππ rescattering in a model independent way.