Fixing the conformal window in QCD
نویسنده
چکیده
A physical characterization of Landau singularities is emphasized, which should trace the lower boundary N f of the conformal window in QCD and supersymmetric QCD. A natural way to disentangle “perturbative” from “non-perturbative” contributions to amplitudes below N f is suggested. Assuming an infrared fixed point persists in the perturbative part of the QCD coupling even below N f leads to the condition γ(N f ) = 1, where γ is the critical exponent. Using the Banks-Zaks expansion, one gets 4 ≤ N f ≤ 6. This result is incompatible with the existence of an analogue of Seiberg duality in QCD. The presence of a negative ultraviolet fixed point is required both in QCD and in supersymmetric QCD to preserve causality within the conformal window. Talk given at the QCDNET2000 network meeting, Paris, September 11-14 2000 (http://qcd.th.u-psud.fr/QCDNET/). Research supported in part by the EC program “Training and Mobility of Researchers”, Network “QCD and Particle Structure”, contract ERBFMRXCT980194.
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