# Unified dispersive approach to $\gamma^*\to\gamma\pi\pi$ and $\gamma\gamma\to\pi\pi$

Abstract : A representation of the amplitude $\gamma^*(q^2)\to\gamma\pi\pi$ is proposed which combines large $N_c$ chiral resonance Lagrangian modelling with general unitarity and analyticity properties. The amplitude is constrained from $\gamma\gamma$ scattering results and $e^+ e^- \to\gamma\pi^0\pi^0$ measurements by the CMD-2 and SND collaborations. As an application, the contribution of the $\pi\pi+\gamma$ states in the HVP contribution to the muon $g-2$ are reconsidered, taking into account the effect of the strong $S$-wave $\pi\pi$ rescattering in a model independent way.
Document type :
Conference papers

http://hal.in2p3.fr/in2p3-00956299
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Submitted on : Thursday, March 6, 2014 - 11:12:20 AM
Last modification on : Wednesday, September 16, 2020 - 4:08:18 PM

### Citation

B. Moussallam. Unified dispersive approach to $\gamma^*\to\gamma\pi\pi$ and $\gamma\gamma\to\pi\pi$. 9th International Workshop on e+ e- collisions from Phi to Psi (PHIPSI13), Sep 2013, Rome, Italy. pp.1460399, ⟨10.1142/S2010194514603998⟩. ⟨in2p3-00956299⟩

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