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Parametrization of the QCD coupling in the Evolution Equations

We examine the parametrization of the QCD coupling in the Evolution Equations, including DGLAP. Our conclusion is that the well-known parametrization, where the argument of the coupling is k^2_{\perp}/βor just k^2_{\perp}, stands only if the lowest integration limit in the transverse momentum space (the starting point mu^2 of the Q^2 -evolution) obeys the relation mu >> Lambda_{QCD} \exp {(π/2)}, otherwise the coupling should be replaced by the more complicated expression presented in Eq. (37).