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arXiv · hep-ph/9512404

Determination of Two-Loop $ππ$ Scattering Amplitude Parameters

M. Knecht·B. Moussallam·J. Stern·N. Fuchs
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Abstract

The chiral expansion of the $ππ$ amplitude to the order of two loops was expressed in terms of six independent parameters in a previous paper: four of these are shown here to satisfy sum rules. Their derivation, where crossing symmetry plays a key role, is explained. Their convergence properties are studied and their practical evaluation, in terms of the available data on $ππ$ phase shifts above 0.5 GeV, is discussed. Below 0.5 GeV, the chiral amplitude itself is employed, such that the parameters are determined in a self-consistent way. Some care is devoted to the estimate of the errors.

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M. Knecht, B. Moussallam, J. Stern, N. Fuchs. 1996-02-07. Determination of Two-Loop $ππ$ Scattering Amplitude Parameters. https://doi.org/10.1016/0550-3213(96)00187-3

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