1 research outputs found
Duality violations and spectral sum rules
We study the issue of duality violations in the VV-AA vacuum polarization
function in the chiral limit. This is done with the help of a model with an
expansion in inverse powers of the number of colors, Nc, allowing us to
consider resonances with a finite width. Due to these duality violations, the
Operator Product Expansion (OPE) and the moments of the spectral function (e.g.
the Weinberg sum rules) do not match at finite momentum, and we analyze this
difference in detail. We also perform a comparative study of many of the
different methods proposed in the literature for the extraction of the OPE
parameters and find that, when applied to our model, they all fare quite
similarly. In fact, the model strongly suggests that a significant improvement
in precision can only be expected after duality violations are included. To
this end, we propose a method to parameterize these duality violations. The
method works quite well for the model, and we hope that it may also be useful
in future determinations of OPE parameters in QCD.Comment: 29 pages, 9 figures, LateX file. Small changes to match journal
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