Comment on the Dispersion Relations used to Calculate Δρ
Grant, Aaron K.
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We use the operator product expansion (OPE) to show that nonperturbative QCD corrections to Δρ can be calculated using unsubtracted dispersion relations for either the transverse or the longitudinal vacuum polarization functions. Recent calculations of the nonperturbative contribution to Δρ based on a non-relativistic calculation of corrections to the t¯t threshold are inconsistent with this result.