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    TH Thursday Seminar

    Fixing the conformal window in QCD

    by Georges GRUNBERG (Ecole Polytechnique)

    → Europe/Zurich
    TH Auditorium (CERN)

    TH Auditorium

    CERN
    Description
    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 below N*f is suggested. Assuming that an infrared fixed point persists in the perturbative part of the QCD coupling even below Nf leads to the condition g (Nf)=1, where g is the critical exponent. Using the Banks-Zaks expansion, one gets 4 < Nf < 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. Evidence for the existence of such a fixed point in QCD is provided.