The 16\half-N_f Expansion and the Infrared Fixed Point in Perturbative QCD

Abstract

In QCD with 16\half-epsilon massless quark flavours there is an infrared fixed point with alpha_s/pi = (8/321)epsilon in the limit epsilon -> 0+. I develop the idea of Banks and Zaks to expand about N_f=16\half. This expansion is certainly useful for N_f=16, 15, 14, ..., and arguably it can reach the phenomenologically interesting case N_f=2, where it suggests that alpha_s/pi "freezes" to a value of order of magnitude 0.4 in the infrared.

10 pages, LaTeX. 3 figures (see top of file). Revised version; some extra discussion. (To appear in Phys. Lett. B.) DE-FG05-92ER40717-12

References in corpus (3)

• Optimization of R(e+e-) and "Freezing" of the QCD Couplant at Low Energies
• QCD Perturbation Theory at Low Energies
• Analytic Multi-Regge Theory and the Pomeron in QCD : II. Gauge Theory Analysis

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• Conformal expansions and renormalons
• Fixing the conformal window in QCD
• Perturbative QCD in acceptable schemes with holomorphic coupling
• Exploring arbitrarily high orders of optimized perturbation theory in QCD with nf -> 16.5
• Pileup and Infrared Radiation Annihilation (PIRANHA): A Paradigm for Continuous Jet Grooming
• The Banks-Zaks expansion in perturbative QCD: an update
• Spiral Multi-component Structure in Pade - Approximant QCD