Heavy quarks and perturbative quantum-chromodynamic calculations

We consider a model universe in which the lightest quarks are heavy on the scale of the QCD $\Lambda$ parameter (however defined). In this model universe we find that there are nonperturbative effects that are not suppressed by powers of $Q^2$. We discuss the implications of such effects in the real world: Residual effects at large $Q^2$ could cause deviations from perturbative predictions.