RS-invariant all-orders renormalon resummations for some QCD observables

RS-Invariant All-Orders Renormalon Resummations for some QCD Observables

We propose a renormalon-inspired resummation of QCD perturbation theory based on approximating the renormalization scheme (RS) invariant effective charge beta-function coefficients by the portion containing the highest power of b=16(11N– 2Nf ), for SU(N) QCD with Nf quark flavours. This can be accomplished using exact large-Nf all-orders results. The resulting resummation is RS-invariant and th...

Ultraviolet Renormalon at All Orders

We discuss the singularity in the Borel plane of the ultraviolet renormalon due to the multiple exchanges of the all-order Gell-Man–Low effective charges. A consistent picture of the UV renormalon emerges when the effective charge is considered in all orders. Contrary to the case of the one-loop effective charge, the strength of the singularity is independent of the number of exchanges. A syste...

All-orders infrared freezing of observables in perturbative QCD

We consider a Borel sum definition of all-orders perturbation theory for Minkowskian QCD observables such as the Re+e− ratio, and show that both this perturbative component and the additional non-perturbative all-orders Operator Product Expansion (OPE) component can remain separately welldefined for all values of energy √ s, with the perturbative component dominating as s → ∞, and with both com...

Sudakov Resummations at Higher Orders ∗

We summarize our recent results on the resummation of hard-scattering coefficient functions and on-shell form factors in massless perturbative QCD. The threshold resummation has been extended to the fourth logarithmic order for deep-inelastic scattering, Drell-Yan lepton pair production and Higgs production via gluon-gluon fusion. The leading six infrared pole terms have been derived to all ord...

Two-loop Resummations for QCD Hard Scattering