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Infrared Factorization, Wilson Lines and the Heavy Quark Limit

It is shown that, in QCD, the same universal function $Γ_{cusp}(\vartheta, α_\s)$ determines the infrared behaviour of the on-shell quark form factor, the velocity-dependent anomalous dimension in the heavy quark effective field theory (HQET) and the renormalization properties of the vacuum averaged Wilson lines with a cusp. It is demonstrated that a combined use of the methods developed in the relevant different branches of quantum field theory essentially facilitates the all-order study of the asymptotic and analytic properties of this function.