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The asymptotics of the transition form factor γγ* -> pi^o and QCD sum rules

A. V. Radyushkin·R. Ruskov
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Abstract

In this paper we present the result of a direct QCD sum rule calculation of the transition form factor γγ* -> pi^o in the region of moderately large invariant momentum Q^2 > 1GeV^2 of the virtual photon. In contrast to pQCD, we make no assumptions about the shape of the pion distribution amplitude ϕ_π(x). Our results agree with the Brodsky-Lepage proposal that the Q^2-dependence of this form factor is given by an interpolation between its Q^2=0 value fixed by the axial anomaly and 1/Q^2 pQCD behaviour for large Q^2, with normalization corresponding to the asymptotic form ϕ_π^as (x)=6 f_πx (1-x) of the pion distribution amplitude. Our prediction for the from factor $F_{γ^*γ^*π^\circ}(q_1^2 = 0,q_2^2 = -Q^2)$ is in good agreement with new CLEO data.

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A. V. Radyushkin, R. Ruskov. 1997-06-26. The asymptotics of the transition form factor γγ* -> pi^o and QCD sum rules. https://arxiv.org/abs/hep-ph/9706518

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