2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49980We give a new criterion of quark confinement/deconfinement by deriving a low-energy effective theory of QCD. The effective theory can explain Abelian dominance in low-energy physics of QCD, especially, quark confinement. Finally, we apply the above criterion to the large flavor QCD and discuss its phase structure. The result suggests the existence of conformal phase.10 pages, 1 figure, Invited talk presented at TMU-Yale Symposium on Dynamics of Gauge Fields, held on December 13-15, 1999High Energy Physics - TheoryHigh Energy Physics - Latticetext